#include "highlighters.hh"

#include "assert.hh"
#include "buffer_utils.hh"
#include "changes.hh"
#include "command_manager.hh"
#include "context.hh"
#include "display_buffer.hh"
#include "face_registry.hh"
#include "highlighter_group.hh"
#include "line_modification.hh"
#include "option.hh"
#include "option_types.hh"
#include "parameters_parser.hh"
#include "ranges.hh"
#include "regex.hh"
#include "register_manager.hh"
#include "string.hh"
#include "utf8.hh"
#include "utf8_iterator.hh"
#include "window.hh"

#include <locale>
#include <cstdio>

namespace Kakoune
{

template<typename Func>
std::unique_ptr<Highlighter> make_highlighter(Func func, HighlightPass pass = HighlightPass::Colorize)
{
    struct SimpleHighlighter : public Highlighter
    {
        SimpleHighlighter(Func func, HighlightPass pass)
          : Highlighter{pass}, m_func{std::move(func)} {}

    private:
        void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange range) override
        {
            m_func(context, display_buffer, range);
        }
        Func m_func;
    };
    return std::make_unique<SimpleHighlighter>(std::move(func), pass);
}

template<typename T>
void highlight_range(DisplayBuffer& display_buffer,
                     BufferCoord begin, BufferCoord end,
                     bool skip_replaced, T func)
{
    // tolerate begin > end as that can be triggered by wrong encodings
    if (begin >= end or end <= display_buffer.range().begin
                     or begin >= display_buffer.range().end)
        return;

    for (auto& line : display_buffer.lines())
    {
        auto& range = line.range();
        if (range.end <= begin or  end < range.begin)
            continue;

        for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
        {
            bool is_replaced = atom_it->type() == DisplayAtom::ReplacedRange;

            if (not atom_it->has_buffer_range() or
                (skip_replaced and is_replaced) or
                end <= atom_it->begin() or begin >= atom_it->end())
                continue;

            if (not is_replaced and begin > atom_it->begin())
                atom_it = ++line.split(atom_it, begin);

            if (not is_replaced and end < atom_it->end())
            {
                atom_it = line.split(atom_it, end);
                func(*atom_it);
                ++atom_it;
            }
            else
                func(*atom_it);
        }
    }
}

template<typename T>
void replace_range(DisplayBuffer& display_buffer,
                   BufferCoord begin, BufferCoord end, T func)
{
    // tolerate begin > end as that can be triggered by wrong encodings
    if (begin >= end or end <= display_buffer.range().begin
                     or begin >= display_buffer.range().end)
        return;

    for (auto& line : display_buffer.lines())
    {
        auto& range = line.range();
        if (range.end <= begin or  end < range.begin)
            continue;

        int beg_idx = -1, end_idx = -1;
        for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
        {
            if (not atom_it->has_buffer_range() or
                end <= atom_it->begin() or begin >= atom_it->end())
                continue;

            if (begin >= atom_it->begin())
            {
                if (begin > atom_it->begin())
                    atom_it = ++line.split(atom_it, begin);
                beg_idx = atom_it - line.begin();
            }
            if (end <= atom_it->end())
            {
                if (end < atom_it->end())
                    atom_it = line.split(atom_it, end);
                end_idx = (atom_it - line.begin()) + 1;
            }
        }

        if (beg_idx != -1 and end_idx != -1)
            func(line, beg_idx, end_idx);
    }
}

void apply_highlighter(HighlightContext context,
                       DisplayBuffer& display_buffer,
                       BufferCoord begin, BufferCoord end,
                       Highlighter& highlighter)
{
    if (begin == end)
        return;

    using LineIterator = DisplayBuffer::LineList::iterator;
    LineIterator first_line;
    Vector<DisplayLine::iterator> insert_pos;
    auto line_end = display_buffer.lines().end();

    DisplayBuffer region_display;
    auto& region_lines = region_display.lines();
    for (auto line_it = display_buffer.lines().begin(); line_it != line_end; ++line_it)
    {
        auto& line = *line_it;
        auto& range = line.range();
        if (range.end <= begin or end <= range.begin)
            continue;

        if (region_lines.empty())
            first_line = line_it;
        region_lines.emplace_back();
        insert_pos.emplace_back();

        if (range.begin < begin or range.end > end)
        {
            size_t beg_idx = 0;
            size_t end_idx = line.atoms().size();

            for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
            {
                if (not atom_it->has_buffer_range() or end <= atom_it->begin() or begin >= atom_it->end())
                    continue;

                bool is_replaced = atom_it->type() == DisplayAtom::ReplacedRange;
                if (atom_it->begin() <= begin)
                {
                    if (is_replaced or atom_it->begin() == begin)
                        beg_idx = atom_it - line.begin();
                    else
                    {
                        atom_it = ++line.split(atom_it, begin);
                        beg_idx = atom_it - line.begin();
                        ++end_idx;
                    }
                }

                if (atom_it->end() >= end)
                {
                    if (is_replaced or atom_it->end() == end)
                        end_idx = atom_it - line.begin() + 1;
                    else
                    {
                        atom_it = ++line.split(atom_it, end);
                        end_idx = atom_it - line.begin();
                    }
                }
            }
            std::move(line.begin() + beg_idx, line.begin() + end_idx,
                      std::back_inserter(region_lines.back()));
            insert_pos.back() = line.erase(line.begin() + beg_idx, line.begin() + end_idx);
        }
        else
        {
            region_lines.back() = std::move(line);
            insert_pos.back() = line.begin();
        }
    }

    if (region_display.lines().empty())
        return;

    region_display.compute_range();
    highlighter.highlight(context, region_display, {begin, end});

    for (size_t i = 0; i < region_lines.size(); ++i)
    {
        auto& line = *(first_line + i);
        auto pos = insert_pos[i];
        for (auto& atom : region_lines[i])
            pos = ++line.insert(pos, std::move(atom));
    }
    display_buffer.compute_range();
}

auto apply_face = [](const Face& face)
{
    return [&face](DisplayAtom& atom) {
        atom.face = merge_faces(atom.face, face);
    };
};

static std::unique_ptr<Highlighter> create_fill_highlighter(HighlighterParameters params, Highlighter*)
{
    if (params.size() != 1)
        throw runtime_error("wrong parameter count");

    const String& facespec = params[0];
    auto func = [facespec](HighlightContext context, DisplayBuffer& display_buffer, BufferRange range)
    {
        highlight_range(display_buffer, range.begin, range.end, false,
                        apply_face(context.context.faces()[facespec]));
    };
    return make_highlighter(std::move(func));
}

template<typename T>
struct BufferSideCache
{
    BufferSideCache() : m_id{get_free_value_id()} {}

    T& get(const Buffer& buffer)
    {
        Value& cache_val = buffer.values()[m_id];
        if (not cache_val)
            cache_val = Value(T{});
        return cache_val.as<T>();
    }
private:
    ValueId m_id;
};

using FacesSpec = Vector<std::pair<size_t, String>, MemoryDomain::Highlight>;

class RegexHighlighter : public Highlighter
{
public:
    RegexHighlighter(Regex regex, FacesSpec faces)
        : Highlighter{HighlightPass::Colorize},
          m_regex{std::move(regex)},
          m_faces{std::move(faces)}
    {
        ensure_first_face_is_capture_0();
    }

    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange range) override
    {
        auto overlaps = [](const BufferRange& lhs, const BufferRange& rhs) {
            return lhs.begin < rhs.begin ? lhs.end > rhs.begin
                                         : rhs.end > lhs.begin;
        };

        if (not overlaps(display_buffer.range(), range))
            return;

        const auto faces = m_faces | transform([&faces = context.context.faces()](auto&& spec) {
                return spec.second.empty() ? Face{} : faces[spec.second];
            }) | gather<Vector<Face>>();

        auto& matches = get_matches(context.context.buffer(), display_buffer.range(), range);
        kak_assert(matches.size() % m_faces.size() == 0);
        for (size_t m = 0; m < matches.size(); ++m)
        {
            auto& face = faces[m % faces.size()];
            if (face == Face{})
                continue;

            highlight_range(display_buffer,
                            matches[m].begin, matches[m].end,
                            false, apply_face(face));
        }
    }

    void reset(Regex regex, FacesSpec faces)
    {
        m_regex = std::move(regex);
        m_faces = std::move(faces);
        ensure_first_face_is_capture_0();
        ++m_regex_version;
    }

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        if (params.size() < 2)
            throw runtime_error("wrong parameter count");

        FacesSpec faces;
        for (auto& spec : params.subrange(1))
        {
            auto colon = find(spec, ':');
            if (colon == spec.end())
                throw runtime_error(format("wrong face spec: '{}' expected <capture>:<facespec>", spec));
            int capture = str_to_int({spec.begin(), colon});
            faces.emplace_back(capture, String{colon+1, spec.end()});
        }

        Regex ex{params[0], RegexCompileFlags::Optimize};

        return std::make_unique<RegexHighlighter>(std::move(ex), std::move(faces));
    }

private:
    // stores the range for each highlighted capture of each match
    using MatchList = Vector<BufferRange, MemoryDomain::Highlight>;
    struct Cache
    {
        size_t m_timestamp = -1;
        size_t m_regex_version = -1;
        struct RangeAndMatches { BufferRange range; MatchList matches; };
        Vector<RangeAndMatches, MemoryDomain::Highlight> m_matches;
    };
    BufferSideCache<Cache> m_cache;

    Regex     m_regex;
    FacesSpec m_faces;

    size_t m_regex_version = 0;

    void ensure_first_face_is_capture_0()
    {
        if (m_faces.empty())
            return;

        std::sort(m_faces.begin(), m_faces.end(),
                  [](const std::pair<size_t, String>& lhs,
                     const std::pair<size_t, String>& rhs)
                  { return lhs.first < rhs.first; });
        if (m_faces[0].first != 0)
            m_faces.emplace(m_faces.begin(), 0, String{});
    }

    void add_matches(const Buffer& buffer, MatchList& matches,
                     BufferRange range)
    {
        kak_assert(matches.size() % m_faces.size() == 0);
        using RegexIt = RegexIterator<BufferIterator>;
        RegexIt re_it{get_iterator(buffer, range.begin),
                      get_iterator(buffer, range.end),
                      buffer.begin(), buffer.end(), m_regex,
                      match_flags(is_bol(range.begin),
                                  is_eol(buffer, range.end),
                                  is_bow(buffer, range.begin),
                                  is_eow(buffer, range.end))};
        RegexIt re_end;
        for (; re_it != re_end; ++re_it)
        {
            for (auto& face : m_faces)
            {
                const auto& sub = (*re_it)[face.first];
                matches.push_back({sub.first.coord(), sub.second.coord()});
            }
        }
    }

    MatchList& get_matches(const Buffer& buffer, BufferRange display_range,
                           BufferRange buffer_range)
    {
        Cache& cache = m_cache.get(buffer);
        auto& matches = cache.m_matches;

        if (cache.m_regex_version != m_regex_version or
            cache.m_timestamp != buffer.timestamp())
        {
            matches.clear();
            cache.m_timestamp = buffer.timestamp();
            cache.m_regex_version = m_regex_version;
        }
        const LineCount line_offset = 3;
        BufferRange range{std::max<BufferCoord>(buffer_range.begin, display_range.begin.line - line_offset),
                          std::min<BufferCoord>(buffer_range.end, display_range.end.line + line_offset)};

        auto it = std::upper_bound(matches.begin(), matches.end(), range,
                                   [](const BufferRange& lhs, const Cache::RangeAndMatches& rhs)
                                   { return lhs.begin < rhs.range.end; });

        if (it == matches.end() or it->range.begin > range.end)
        {
            it = matches.insert(it, Cache::RangeAndMatches{range, {}});
            add_matches(buffer, it->matches, range);
        }
        else if (it->matches.empty())
        {
            it->range = range;
            add_matches(buffer, it->matches, range);
        }
        else
        {
            // Here we extend the matches, that is not strictly valid,
            // but may work nicely with every reasonable regex, and
            // greatly reduces regex parsing. To change if we encounter
            // regex that do not work great with that.
            BufferRange& old_range = it->range;
            MatchList& matches = it->matches;

            // Thanks to the ensure_first_face_is_capture_0 method, we know
            // these point to the first/last matches capture 0.
            auto first_end = matches.begin()->end;
            auto last_end = (matches.end() - m_faces.size())->end;

            // add regex matches from new begin to old first match end
            if (range.begin < old_range.begin)
            {
                old_range.begin = range.begin;
                MatchList new_matches;
                add_matches(buffer, new_matches, {range.begin, first_end});
                matches.erase(matches.begin(), matches.begin() + m_faces.size());

                std::copy(std::make_move_iterator(new_matches.begin()),
                          std::make_move_iterator(new_matches.end()),
                          std::inserter(matches, matches.begin()));
            }
            // add regex matches from old last match begin to new end
            if (old_range.end < range.end)
            {
                old_range.end = range.end;
                add_matches(buffer, matches, {last_end, range.end});
            }
        }
        return it->matches;
    }
};

template<typename RegexGetter, typename FaceGetter>
class DynamicRegexHighlighter : public Highlighter
{
public:
    DynamicRegexHighlighter(RegexGetter regex_getter, FaceGetter face_getter)
      : Highlighter{HighlightPass::Colorize},
        m_regex_getter(std::move(regex_getter)),
        m_face_getter(std::move(face_getter)),
        m_highlighter(Regex{}, FacesSpec{}) {}

    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange range) override
    {
        Regex regex = m_regex_getter(context.context);
        FacesSpec face = m_face_getter(context.context);
        if (regex != m_last_regex or face != m_last_face)
        {
            m_last_regex = std::move(regex);
            m_last_face = face;
            if (not m_last_regex.empty())
                m_highlighter.reset(m_last_regex, m_last_face);
        }
        if (not m_last_regex.empty() and not m_last_face.empty())
            m_highlighter.highlight(context, display_buffer, range);
    }

private:
    Regex       m_last_regex;
    RegexGetter m_regex_getter;

    FacesSpec   m_last_face;
    FaceGetter  m_face_getter;

    RegexHighlighter m_highlighter;
};

std::unique_ptr<Highlighter> create_dynamic_regex_highlighter(HighlighterParameters params, Highlighter*)
{
    if (params.size() < 2)
        throw runtime_error("wrong parameter count");

    FacesSpec faces;
    for (auto& spec : params.subrange(1))
    {
        auto colon = find(spec, ':');
        if (colon == spec.end())
            throw runtime_error("wrong face spec: '" + spec +
                                 "' expected <capture>:<facespec>");
        int capture = str_to_int({spec.begin(), colon});
        faces.emplace_back(capture, String{colon+1, spec.end()});
    }


    auto make_hl = [](auto& regex_getter, auto& face_getter) {
        return std::make_unique<DynamicRegexHighlighter<std::decay_t<decltype(regex_getter)>,
                                                        std::decay_t<decltype(face_getter)>>>(
            std::move(regex_getter), std::move(face_getter));
    };
    auto get_face = [faces](const Context& context){ return faces; };

    CommandParser parser{params[0]};
    auto token = parser.read_token(true);
    if (token and parser.done() and token->type == Token::Type::OptionExpand and
        GlobalScope::instance().options()[token->content].is_of_type<Regex>())
    {
        auto get_regex = [option_name = token->content](const Context& context) {
            return context.options()[option_name].get<Regex>();
        };
        return make_hl(get_regex, get_face);
    }

    auto get_regex = [expr = params[0]](const Context& context){
        try
        {
            auto re = expand(expr, context);
            return re.empty() ? Regex{} : Regex{re};
        }
        catch (runtime_error& err)
        {
            write_to_debug_buffer(format("Error while evaluating dynamic regex expression: {}", err.what()));
            return Regex{};
        }
    };
    return make_hl(get_regex, get_face);
}

std::unique_ptr<Highlighter> create_line_highlighter(HighlighterParameters params, Highlighter*)
{
    if (params.size() != 2)
        throw runtime_error("wrong parameter count");

    auto func = [line_expr=params[0], facespec=params[1]]
                (HighlightContext context, DisplayBuffer& display_buffer, BufferRange)
    {
        LineCount line = -1;
        try
        {
            line = str_to_int_ifp(expand(line_expr, context.context)).value_or(0) - 1;
        }
        catch (runtime_error& err)
        {
            write_to_debug_buffer(
                format("Error evaluating highlight line expression: {}", err.what()));
        }

        if (line < 0)
            return;

        auto it = find_if(display_buffer.lines(),
                          [line](const DisplayLine& l)
                          { return l.range().begin.line == line; });
        if (it == display_buffer.lines().end())
            return;

        auto face = context.context.faces()[facespec];
        ColumnCount column = 0;
        for (auto& atom : *it)
        {
            column += atom.length();
            if (!atom.has_buffer_range())
                continue;

            kak_assert(atom.begin().line == line);
            apply_face(face)(atom);
        }
        const ColumnCount remaining = context.context.window().dimensions().column - column;
        if (remaining > 0)
            it->push_back({ String{' ', remaining}, face });
    };

    return make_highlighter(std::move(func));
}

std::unique_ptr<Highlighter> create_column_highlighter(HighlighterParameters params, Highlighter*)
{
    if (params.size() != 2)
        throw runtime_error("wrong parameter count");

    auto func = [col_expr=params[0], facespec=params[1]]
                (HighlightContext context, DisplayBuffer& display_buffer, BufferRange)
    {
        ColumnCount column = -1;
        try
        {
            column = str_to_int_ifp(expand(col_expr, context.context)).value_or(0) - 1;
        }
        catch (runtime_error& err)
        {
            write_to_debug_buffer(
                format("Error evaluating highlight column expression: {}", err.what()));
        }

        if (column < 0)
            return;

        auto face = context.context.faces()[facespec];
        auto win_column = context.setup.window_pos.column;
        for (auto& line : display_buffer.lines())
        {
            auto target_col = column - win_column;
            if (target_col < 0)
                return;

            bool found = false;
            auto first_buf = find_if(line, [](auto& atom) { return atom.has_buffer_range(); });
            for (auto atom_it = first_buf; atom_it != line.end(); ++atom_it)
            {
                const auto atom_len = atom_it->length();
                if (target_col < atom_len)
                {
                    if (target_col > 0)
                        atom_it = ++line.split(atom_it, target_col);
                    if (atom_it->length() > 1)
                        atom_it = line.split(atom_it, 1_col);
                    atom_it->face = merge_faces(atom_it->face, face);
                    found = true;
                    break;
                }
                target_col -= atom_len;
            }
            if (found)
                continue;

            if (target_col > 0)
                line.push_back({String{' ', target_col}, {}});
            line.push_back({" ", face});
        }
    };

    return make_highlighter(std::move(func));
}

struct WrapHighlighter : Highlighter
{
    WrapHighlighter(ColumnCount max_width, bool word_wrap, bool preserve_indent, String marker)
        : Highlighter{HighlightPass::Wrap}, m_max_width{max_width},
          m_word_wrap{word_wrap}, m_preserve_indent{preserve_indent},
          m_marker{std::move(marker)} {}

    static constexpr StringView ms_id = "wrap";

    struct SplitPos{ ByteCount byte; ColumnCount column; };

    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange) override
    {
        if (contains(context.disabled_ids, ms_id))
            return;

        const ColumnCount wrap_column = std::min(m_max_width, context.setup.window_range.column);
        if (wrap_column <= 0)
            return;

        const Buffer& buffer = context.context.buffer();
        const auto& cursor = context.context.selections().main().cursor();
        const int tabstop = context.context.options()["tabstop"].get<int>();
        const LineCount win_height = context.context.window().dimensions().line;
        const ColumnCount marker_len = m_marker.column_length();
        const Face face_marker = context.context.faces()["StatusLineInfo"];
        for (auto it = display_buffer.lines().begin();
             it != display_buffer.lines().end(); ++it)
        {
            const LineCount buf_line = it->range().begin.line;
            const ByteCount line_length = buffer[buf_line].length();
            const ColumnCount indent = m_preserve_indent ? line_indent(buffer, tabstop, buf_line) : 0_col;

            auto pos = next_split_pos(buffer, wrap_column, tabstop, buf_line, {0, 0});
            if (pos.byte == line_length)
                continue;

            for (auto atom_it = it->begin();
                 pos.byte != line_length and atom_it != it->end(); )
            {
                const BufferCoord coord{buf_line, pos.byte};
                if (!atom_it->has_buffer_range() or
                    coord < atom_it->begin() or coord >= atom_it->end())
                {
                    ++atom_it;
                    continue;
                }

                auto& line = *it;

                if (coord > atom_it->begin())
                    atom_it = ++line.split(atom_it, coord);

                DisplayLine new_line{ AtomList{ atom_it, line.end() } };
                line.erase(atom_it, line.end());

                ColumnCount prefix_len = 0;
                if (marker_len != 0 and marker_len < wrap_column)
                {
                    new_line.insert(new_line.begin(), {m_marker, face_marker});
                    prefix_len = marker_len;
                }
                if (indent > marker_len and indent < wrap_column)
                {
                    auto it = new_line.insert(new_line.begin() + (marker_len > 0), {buffer, coord, coord});
                    it->replace(String{' ', indent - marker_len});
                    prefix_len = indent;
                }

                if (it+1 - display_buffer.lines().begin() == win_height)
                {
                    if (cursor >= new_line.range().begin) // strip first lines if cursor is not visible
                    {
                        display_buffer.lines().erase(display_buffer.lines().begin(), display_buffer.lines().begin()+1);
                        --it;
                    }
                    else
                    {
                        display_buffer.lines().erase(it+1, display_buffer.lines().end());
                        return;
                    }
                }
                it = display_buffer.lines().insert(it+1, new_line);

                pos = next_split_pos(buffer, wrap_column - prefix_len, tabstop, buf_line, pos);
                atom_it = it->begin();
            }
        }
    }

    void do_compute_display_setup(HighlightContext context, DisplaySetup& setup) const override
    {
        if (contains(context.disabled_ids, ms_id))
            return;

        const ColumnCount wrap_column = std::min(setup.window_range.column, m_max_width);
        if (wrap_column <= 0)
            return;

        const Buffer& buffer = context.context.buffer();
        const auto& cursor = context.context.selections().main().cursor();
        const int tabstop = context.context.options()["tabstop"].get<int>();

        auto line_wrap_count = [&](LineCount line, ColumnCount indent) {
            LineCount count = 0;
            const ByteCount line_length = buffer[line].length();
            SplitPos pos{0, 0};
            while (true)
            {
                pos = next_split_pos(buffer, wrap_column - (pos.byte == 0 ? 0_col : indent),
                                     tabstop, line, pos);
                if (pos.byte == line_length)
                    break;
                ++count;
            }
            return count;
        };

        const auto win_height = context.context.window().dimensions().line;

        // Disable horizontal scrolling when using a WrapHighlighter
        setup.window_pos.column = 0;
        setup.window_range.line = 0;
        setup.scroll_offset.column = 0;
        setup.full_lines = true;

        const ColumnCount marker_len = m_marker.column_length();

        for (auto buf_line = setup.window_pos.line, win_line = 0_line;
             win_line < win_height or buf_line <= cursor.line;
             ++buf_line, ++setup.window_range.line)
        {
            if (buf_line >= buffer.line_count())
                break;

            const ColumnCount indent = m_preserve_indent ? line_indent(buffer, tabstop, buf_line) : 0_col;

            ColumnCount prefix_len = 0;
            if (marker_len < wrap_column)
                prefix_len = marker_len;
            if (indent > marker_len and indent < wrap_column)
                prefix_len = indent;

            if (buf_line == cursor.line)
            {
                SplitPos pos{0, 0};
                for (LineCount count = 0; true; ++count)
                {
                    auto next_pos = next_split_pos(buffer, wrap_column - (pos.byte != 0 ? prefix_len : 0_col),
                                                   tabstop, buf_line, pos);
                    if (next_pos.byte > cursor.column)
                    {
                        setup.cursor_pos = DisplayCoord{
                            win_line + count,
                            get_column(buffer, tabstop, cursor) -
                            pos.column + (pos.byte != 0 ? indent : 0_col)
                        };
                        break;
                    }
                    pos = next_pos;
                }
                kak_assert(setup.cursor_pos.column >= 0 and setup.cursor_pos.column < setup.window_range.column);
            }
            const auto wrap_count = line_wrap_count(buf_line, prefix_len);
            win_line += wrap_count + 1;

            // scroll window to keep cursor visible, and update range as lines gets removed
            while (buf_line >= cursor.line and setup.window_pos.line < cursor.line and
                   setup.cursor_pos.line + setup.scroll_offset.line >= win_height)
            {
                auto remove_count = std::min(win_height, 1 + line_wrap_count(setup.window_pos.line, indent));
                ++setup.window_pos.line;
                --setup.window_range.line;
                setup.cursor_pos.line -= remove_count;
                win_line -= remove_count;
                kak_assert(setup.cursor_pos.line >= 0);
            }
        }
    }

    void fill_unique_ids(Vector<StringView>& unique_ids) const override
    {
        unique_ids.push_back(ms_id);
    }

    SplitPos next_split_pos(const Buffer& buffer,  ColumnCount wrap_column, int tabstop, LineCount line, SplitPos current) const
    {
        const ColumnCount target_column = current.column + wrap_column;
        StringView content = buffer[line];

        SplitPos pos = current;
        SplitPos last_boundary = {0, 0};

        while (pos.byte < content.length() and pos.column < target_column)
        {
            if (content[pos.byte] == '\t')
            {
                const ColumnCount next_column = (pos.column / tabstop + 1) * tabstop;
                if (next_column > target_column and pos.byte != current.byte) // the target column was in the tab
                    break;
                pos.column = next_column;
                ++pos.byte;
                last_boundary = pos;
            }
            else
            {
                const char* it = &content[pos.byte];
                const Codepoint cp = utf8::read_codepoint(it, content.end());
                const ColumnCount width = codepoint_width(cp);
                if (pos.column + width > target_column and pos.byte != current.byte) // the target column was in the char
                {
                    if (!is_word<WORD>(cp))
                        last_boundary = pos;
                    break;
                }
                pos.column += width;
                pos.byte = (int)(it - content.begin());
                if (!is_word<WORD>(cp))
                    last_boundary = pos;
            }
        }

        if (m_word_wrap and pos.byte < content.length()) // find a word boundary before current position
            if (last_boundary.byte > 0)
                pos = last_boundary;

        return pos;
    };

    ColumnCount line_indent(const Buffer& buffer, int tabstop, LineCount line) const
    {
        StringView l = buffer[line];
        auto col = 0_byte;
        while (is_horizontal_blank(l[col]))
               ++col;
        return get_column(buffer, tabstop, {line, col});
    }

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        static const ParameterDesc param_desc{
            { { "word", { false, "" } },
              { "indent", { false, "" } },
              { "width", { true, "" } },
              { "marker", { true, "" } } },
            ParameterDesc::Flags::None, 0, 0
        };
        ParametersParser parser(params, param_desc);

        ColumnCount max_width{std::numeric_limits<int>::max()};
        if (auto width = parser.get_switch("width"))
            max_width = str_to_int(*width);

        return std::make_unique<WrapHighlighter>(max_width, (bool)parser.get_switch("word"),
                                                 (bool)parser.get_switch("indent"),
                                                 parser.get_switch("marker").value_or("").str());
    }

    const bool m_word_wrap;
    const bool m_preserve_indent;
    const ColumnCount m_max_width;
    const String m_marker;
};

constexpr StringView WrapHighlighter::ms_id;

struct TabulationHighlighter : Highlighter
{
    TabulationHighlighter() : Highlighter{HighlightPass::Move} {}

    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange) override
    {
        const ColumnCount tabstop = context.context.options()["tabstop"].get<int>();
        auto& buffer = context.context.buffer();
        auto win_column = context.setup.window_pos.column;
        for (auto& line : display_buffer.lines())
        {
            for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
            {
                if (atom_it->type() != DisplayAtom::Range)
                    continue;

                auto begin = get_iterator(buffer, atom_it->begin());
                auto end = get_iterator(buffer, atom_it->end());
                for (BufferIterator it = begin; it != end; ++it)
                {
                    if (*it == '\t')
                    {
                        if (it != begin)
                            atom_it = ++line.split(atom_it, it.coord());
                        if (it+1 != end)
                            atom_it = line.split(atom_it, (it+1).coord());

                        const ColumnCount column = get_column(buffer, tabstop, it.coord());
                        const ColumnCount count = tabstop - (column % tabstop) -
                                                  std::max(win_column - column, 0_col);
                        atom_it->replace(String{' ', count});
                        break;
                    }
                }
            }
        }
    }

    void do_compute_display_setup(HighlightContext context, DisplaySetup& setup) const override
    {
        auto& buffer = context.context.buffer();
        // Ensure that a cursor on a tab character makes the full tab character visible
        auto cursor = context.context.selections().main().cursor();
        if (buffer.byte_at(cursor) != '\t')
            return;

        const ColumnCount tabstop = context.context.options()["tabstop"].get<int>();
        const ColumnCount column = get_column(buffer, tabstop, cursor);
        const ColumnCount width = tabstop - (column % tabstop);
        const ColumnCount win_end = setup.window_pos.column + setup.window_range.column;
        const ColumnCount offset = std::max(column + width - win_end, 0_col);

        setup.window_pos.column += offset;
        setup.cursor_pos.column -= offset;
    }
};

struct ShowWhitespacesHighlighter : Highlighter
{
    ShowWhitespacesHighlighter(String tab, String tabpad, String spc, String lf, String nbsp)
      : Highlighter{HighlightPass::Move}, m_tab{std::move(tab)}, m_tabpad{std::move(tabpad)},
        m_spc{std::move(spc)}, m_lf{std::move(lf)}, m_nbsp{std::move(nbsp)}
    {}

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        static const ParameterDesc param_desc{
            { { "tab", { true, "" } },
              { "tabpad", { true, "" } },
              { "spc", { true, "" } },
              { "lf", { true, "" } },
              { "nbsp", { true, "" } } },
            ParameterDesc::Flags::None, 0, 0
        };
        ParametersParser parser(params, param_desc);

        auto get_param = [&](StringView param,  StringView fallback) {
            StringView value = parser.get_switch(param).value_or(fallback);
            if (value.char_length() != 1)
                throw runtime_error{format("-{} expects a single character parameter", param)};
            return value.str();
        };

        return std::make_unique<ShowWhitespacesHighlighter>(
            get_param("tab", "→"), get_param("tabpad", " "), get_param("spc", "·"),
            get_param("lf", "¬"), get_param("nbsp", "⍽"));
    }

private:
    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange)
    {
        const int tabstop = context.context.options()["tabstop"].get<int>();
        auto whitespaceface = context.context.faces()["Whitespace"];
        auto& buffer = context.context.buffer();
        auto win_column = context.setup.window_pos.column;
        for (auto& line : display_buffer.lines())
        {
            for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
            {
                if (atom_it->type() != DisplayAtom::Range)
                    continue;

                auto begin = get_iterator(buffer, atom_it->begin());
                auto end = get_iterator(buffer, atom_it->end());
                for (BufferIterator it = begin; it != end; )
                {
                    auto coord = it.coord();
                    Codepoint cp = utf8::read_codepoint(it, end);
                    if (cp == '\t' or cp == ' ' or cp == '\n' or cp == 0xA0)
                    {
                        if (coord != begin.coord())
                            atom_it = ++line.split(atom_it, coord);
                        if (it != end)
                            atom_it = line.split(atom_it, it.coord());

                        if (cp == '\t')
                        {
                            const ColumnCount column = get_column(buffer, tabstop, coord);
                            const ColumnCount count = tabstop - (column % tabstop) -
                                                      std::max(win_column - column, 0_col);
                            atom_it->replace(m_tab + String(m_tabpad[(CharCount)0], count - m_tab.column_length()));
                        }
                        else if (cp == ' ')
                            atom_it->replace(m_spc);
                        else if (cp == '\n')
                            atom_it->replace(m_lf);
                        else if (cp == 0xA0)
                            atom_it->replace(m_nbsp);
                        atom_it->face = merge_faces(atom_it->face, whitespaceface);
                        break;
                    }
                }
            }
        }
    }

    const String m_tab, m_tabpad, m_spc, m_lf, m_nbsp;
};

struct LineNumbersHighlighter : Highlighter
{
    LineNumbersHighlighter(bool relative, bool hl_cursor_line, String separator)
      : Highlighter{HighlightPass::Move},
        m_relative{relative},
        m_hl_cursor_line{hl_cursor_line},
        m_separator{std::move(separator)} {}

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        static const ParameterDesc param_desc{
            { { "relative", { false, "" } },
              { "separator", { true, "" } },
              { "hlcursor", { false, "" } } },
            ParameterDesc::Flags::None, 0, 0
        };
        ParametersParser parser(params, param_desc);

        StringView separator = parser.get_switch("separator").value_or("│");
        if (separator.length() > 10)
            throw runtime_error("separator length is limited to 10 bytes");

        return std::make_unique<LineNumbersHighlighter>((bool)parser.get_switch("relative"), (bool)parser.get_switch("hlcursor"), separator.str());
    }

private:
    static constexpr StringView ms_id = "line-numbers";

    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange) override
    {
        if (contains(context.disabled_ids, ms_id))
            return;

        auto& faces = context.context.faces();
        const Face face = faces["LineNumbers"];
        const Face face_wrapped = faces["LineNumbersWrapped"];
        const Face face_absolute = faces["LineNumberCursor"];
        int digit_count = compute_digit_count(context.context);

        char format[16];
        format_to(format, "%{}d", digit_count);
        const int main_line = (int)context.context.selections().main().cursor().line + 1;
        int last_line = -1;
        for (auto& line : display_buffer.lines())
        {
            const int current_line = (int)line.range().begin.line + 1;
            const bool is_cursor_line = main_line == current_line;
            const int line_to_format = (m_relative and not is_cursor_line) ?
                                       current_line - main_line : current_line;
            char buffer[16];
            snprintf(buffer, 16, format, std::abs(line_to_format));
            const auto atom_face = last_line == current_line ? face_wrapped :
                ((m_hl_cursor_line and is_cursor_line) ? face_absolute : face);
            line.insert(line.begin(), {buffer, atom_face});
            line.insert(line.begin() + 1, {m_separator, face});

            last_line = current_line;
        }
    }

    void do_compute_display_setup(HighlightContext context, DisplaySetup& setup) const override
    {
        if (contains(context.disabled_ids, ms_id))
            return;

        ColumnCount width = compute_digit_count(context.context) + m_separator.column_length();
        setup.window_range.column -= std::min(width, setup.window_range.column);
    }

    void fill_unique_ids(Vector<StringView>& unique_ids) const override
    {
        unique_ids.push_back(ms_id);
    }

    int compute_digit_count(const Context& context) const
    {
        int digit_count = 0;
        LineCount last_line = context.buffer().line_count();
        for (LineCount c = last_line; c > 0; c /= 10)
            ++digit_count;
        return digit_count;
    }

   const bool m_relative;
   const bool m_hl_cursor_line;
   const String m_separator;
};

constexpr StringView LineNumbersHighlighter::ms_id;


void show_matching_char(HighlightContext context, DisplayBuffer& display_buffer, BufferRange)
{
    const Face face = context.context.faces()["MatchingChar"];
    using CodepointPair = std::pair<Codepoint, Codepoint>;
    static const CodepointPair matching_chars[] = { { '(', ')' }, { '{', '}' }, { '[', ']' }, { '<', '>' } };
    const auto range = display_buffer.range();
    const auto& buffer = context.context.buffer();
    for (auto& sel : context.context.selections())
    {
        auto pos = sel.cursor();
        if (pos < range.begin or pos >= range.end)
            continue;
        auto c = buffer.byte_at(pos);
        for (auto& pair : matching_chars)
        {
            int level = 1;
            if (c == pair.first)
            {
                for (auto it = get_iterator(buffer, pos)+1,
                         end = get_iterator(buffer, range.end); it != end; ++it)
                {
                    char c = *it;
                    if (c == pair.first)
                        ++level;
                    else if (c == pair.second and --level == 0)
                    {
                        highlight_range(display_buffer, it.coord(), (it+1).coord(), false,
                                        apply_face(face));
                        break;
                    }
                }
            }
            else if (c == pair.second and pos > range.begin)
            {
                for (auto it = get_iterator(buffer, pos)-1,
                         end = get_iterator(buffer, range.begin); true; --it)
                {
                    char c = *it;
                    if (c == pair.second)
                        ++level;
                    else if (c == pair.first and --level == 0)
                    {
                        highlight_range(display_buffer, it.coord(), (it+1).coord(), false,
                                        apply_face(face));
                        break;
                    }
                    if (it == end)
                        break;
                }
            }
        }
    }
}

std::unique_ptr<Highlighter> create_matching_char_highlighter(HighlighterParameters params, Highlighter*)
{
    return make_highlighter(show_matching_char);
}

void highlight_selections(HighlightContext context, DisplayBuffer& display_buffer, BufferRange)
{
    const auto& buffer = context.context.buffer();
    const auto& faces = context.context.faces();
    const Face sel_faces[6] = {
            faces["PrimarySelection"], faces["SecondarySelection"],
            faces["PrimaryCursor"],    faces["SecondaryCursor"],
            faces["PrimaryCursorEol"], faces["SecondaryCursorEol"],
    };

    const auto& selections = context.context.selections();
    for (size_t i = 0; i < selections.size(); ++i)
    {
        auto& sel = selections[i];
        const bool forward = sel.anchor() <= sel.cursor();
        BufferCoord begin = forward ? sel.anchor() : buffer.char_next(sel.cursor());
        BufferCoord end   = forward ? (BufferCoord)sel.cursor() : buffer.char_next(sel.anchor());

        const bool primary = (i == selections.main_index());
        highlight_range(display_buffer, begin, end, false,
                        apply_face(sel_faces[primary ? 0 : 1]));
    }
    for (size_t i = 0; i < selections.size(); ++i)
    {
        auto& sel = selections[i];
        const BufferCoord coord = sel.cursor();
        const bool primary = (i == selections.main_index());
        const bool eol = buffer[coord.line].length() - 1 == coord.column;
        highlight_range(display_buffer, coord, buffer.char_next(coord), false,
                        apply_face(sel_faces[2 + (eol ? 2 : 0) + (primary ? 0 : 1)]));
    }
}

void expand_unprintable(HighlightContext context, DisplayBuffer& display_buffer, BufferRange)
{
    auto& buffer = context.context.buffer();
    auto error = context.context.faces()["Error"];
    for (auto& line : display_buffer.lines())
    {
        for (auto atom_it = line.begin(); atom_it != line.end(); ++atom_it)
        {
            if (atom_it->type() == DisplayAtom::Range)
            {
                for (auto it  = get_iterator(buffer, atom_it->begin()),
                          end = get_iterator(buffer, atom_it->end()); it < end;)
                {
                    auto coord = it.coord();
                    Codepoint cp = utf8::read_codepoint(it, end);
                    if (cp != '\n' and not iswprint((wchar_t)cp))
                    {
                        if (coord != atom_it->begin())
                            atom_it = ++line.split(atom_it, coord);
                        if (it.coord() < atom_it->end())
                            atom_it = line.split(atom_it, it.coord());

                        atom_it->replace("�");
                        atom_it->face = error;
                        break;
                    }
                }
            }
        }
    }
}

static void update_line_specs_ifn(const Buffer& buffer, LineAndSpecList& line_flags)
{
    if (line_flags.prefix == buffer.timestamp())
        return;

    auto& lines = line_flags.list;

    auto modifs = compute_line_modifications(buffer, line_flags.prefix);
    auto ins_pos = lines.begin();
    for (auto it = lines.begin(); it != lines.end(); ++it)
    {
        auto& line = std::get<0>(*it); // that line is 1 based as it comes from user side
        auto modif_it = std::upper_bound(modifs.begin(), modifs.end(), line-1,
                                         [](const LineCount& l, const LineModification& c)
                                         { return l < c.old_line; });
        if (modif_it != modifs.begin())
        {
            auto& prev = *(modif_it-1);
            if (line-1 < prev.old_line + prev.num_removed)
                continue; // line removed

            line += prev.diff();
        }

        if (ins_pos != it)
            *ins_pos = std::move(*it);
        ++ins_pos;
    }
    lines.erase(ins_pos, lines.end());
    line_flags.prefix = buffer.timestamp();
}

void option_update(LineAndSpecList& opt, const Context& context)
{
    update_line_specs_ifn(context.buffer(), opt);
}

void option_list_postprocess(Vector<LineAndSpec, MemoryDomain::Options>& opt)
{
    std::sort(opt.begin(), opt.end(),
              [](auto& lhs, auto& rhs)
              { return std::get<0>(lhs) < std::get<0>(rhs); });
}

struct FlagLinesHighlighter : Highlighter
{
    FlagLinesHighlighter(String option_name, String default_face)
        : Highlighter{HighlightPass::Move},
          m_option_name{std::move(option_name)},
          m_default_face{std::move(default_face)} {}

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        if (params.size() != 2)
            throw runtime_error("wrong parameter count");

        const String& option_name = params[1];
        const String& default_face = params[0];

        // throw if wrong option type
        GlobalScope::instance().options()[option_name].get<LineAndSpecList>();

        return std::make_unique<FlagLinesHighlighter>(option_name, default_face);
    }

private:
    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange) override
    {
        auto& line_flags = context.context.options()[m_option_name].get_mutable<LineAndSpecList>();
        auto& buffer = context.context.buffer();
        update_line_specs_ifn(buffer, line_flags);

        auto def_face = context.context.faces()[m_default_face];
        Vector<DisplayLine> display_lines;
        auto& lines = line_flags.list;
        try
        {
            for (auto& line : lines)
            {
                display_lines.push_back(parse_display_line(std::get<1>(line), context.context.faces()));
                for (auto& atom : display_lines.back())
                    atom.face = merge_faces(def_face, atom.face);
            }
        }
        catch (runtime_error& err)
        {
            write_to_debug_buffer(format("Error while evaluating line flag: {}", err.what()));
            return;
        }

        ColumnCount width = 0;
        for (auto& l : display_lines)
             width = std::max(width, l.length());
        const DisplayAtom empty{String{' ', width}, def_face};
        for (auto& line : display_buffer.lines())
        {
            int line_num = (int)line.range().begin.line + 1;
            auto it = find_if(lines,
                              [&](const LineAndSpec& l)
                              { return std::get<0>(l) == line_num; });
            if (it == lines.end())
                line.insert(line.begin(), empty);
            else
            {
                DisplayLine& display_line = display_lines[it - lines.begin()];
                DisplayAtom padding_atom{String(' ', width - display_line.length()), def_face};
                auto it = std::copy(std::make_move_iterator(display_line.begin()),
                                    std::make_move_iterator(display_line.end()),
                                    std::inserter(line, line.begin()));

                if (padding_atom.length() != 0)
                    *it++ = std::move(padding_atom);
            }
        }
    }

    void do_compute_display_setup(HighlightContext context, DisplaySetup& setup) const override
    {
        auto& line_flags = context.context.options()[m_option_name].get_mutable<LineAndSpecList>();
        auto& buffer = context.context.buffer();
        update_line_specs_ifn(buffer, line_flags);

        ColumnCount width = 0;
        try
        {
            for (auto& line : line_flags.list)
                width = std::max(parse_display_line(std::get<1>(line), context.context.faces()).length(), width);
        }
        catch (runtime_error& err)
        {
            write_to_debug_buffer(format("Error while evaluating line flag: {}", err.what()));
            return;
        }

        setup.window_range.column -= std::min(width, setup.window_range.column);
    }

    String m_option_name;
    String m_default_face;
};

String option_to_string(InclusiveBufferRange range)
{
    return format("{}.{},{}.{}",
                  range.first.line+1, range.first.column+1,
                  range.last.line+1, range.last.column+1);
}

InclusiveBufferRange option_from_string(Meta::Type<InclusiveBufferRange>, StringView str)
{
    auto sep = find_if(str, [](char c){ return c == ',' or c == '+'; });
    auto dot_beg = find(StringView{str.begin(), sep}, '.');
    auto dot_end = find(StringView{sep, str.end()}, '.');

    if (sep == str.end() or dot_beg == sep or
        (*sep == ',' and dot_end == str.end()))
        throw runtime_error(format("'{}' does not follow <line>.<column>,<line>.<column> or <line>.<column>+<len> format", str));

    const BufferCoord first{str_to_int({str.begin(), dot_beg}) - 1,
                            str_to_int({dot_beg+1, sep}) - 1};

    const bool len = (*sep == '+');
    const BufferCoord last{len ? first.line : str_to_int({sep+1, dot_end}) - 1,
                           len ? first.column + str_to_int({sep+1, str.end()}) - 1
                               : str_to_int({dot_end+1, str.end()}) - 1 };

    if (first.line < 0 or first.column < 0 or last.line < 0 or last.column < 0)
        throw runtime_error("coordinates elements should be >= 1");

    return { std::min(first, last), std::max(first, last) };
}

BufferCoord& get_first(RangeAndString& r) { return std::get<0>(r).first; }
BufferCoord& get_last(RangeAndString& r) { return std::get<0>(r).last; }

void option_list_postprocess(Vector<RangeAndString, MemoryDomain::Options>& opt)
{
    std::sort(opt.begin(), opt.end(),
              [](auto& lhs, auto& rhs) {
        return std::get<0>(lhs).first == std::get<0>(rhs).first ?
            std::get<0>(lhs).last < std::get<0>(rhs).last
          : std::get<0>(lhs).first < std::get<0>(rhs).first;
    });
}

void option_update(RangeAndStringList& opt, const Context& context)
{
    update_ranges(context.buffer(), opt.prefix, opt.list);
}

struct RangesHighlighter : Highlighter
{
    RangesHighlighter(String option_name)
        : Highlighter{HighlightPass::Colorize}
        , m_option_name{std::move(option_name)} {}

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        if (params.size() != 1)
            throw runtime_error("wrong parameter count");

        const String& option_name = params[0];
        // throw if wrong option type
        GlobalScope::instance().options()[option_name].get<RangeAndStringList>();

        return std::make_unique<RangesHighlighter>(option_name);
    }

private:
    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange) override
    {
        auto& buffer = context.context.buffer();
        auto& range_and_faces = context.context.options()[m_option_name].get_mutable<RangeAndStringList>();
        update_ranges(buffer, range_and_faces.prefix, range_and_faces.list);

        for (auto& range : range_and_faces.list)
        {
            try
            {
                auto& r = std::get<0>(range);
                if (buffer.is_valid(r.first) and (buffer.is_valid(r.last) and not buffer.is_end(r.last)))
                    highlight_range(display_buffer, r.first, buffer.char_next(r.last), false,
                                    apply_face(context.context.faces()[std::get<1>(range)]));
            }
            catch (runtime_error&)
            {}
        }
    }

    const String m_option_name;
};

struct ReplaceRangesHighlighter : Highlighter
{
    ReplaceRangesHighlighter(String option_name)
        : Highlighter{HighlightPass::Colorize}
        , m_option_name{std::move(option_name)} {}

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        if (params.size() != 1)
            throw runtime_error("wrong parameter count");

        const String& option_name = params[0];
        // throw if wrong option type
        GlobalScope::instance().options()[option_name].get<RangeAndStringList>();

        return std::make_unique<ReplaceRangesHighlighter>(option_name);
    }

private:
    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange) override
    {
        auto& buffer = context.context.buffer();
        auto& range_and_faces = context.context.options()[m_option_name].get_mutable<RangeAndStringList>();
        update_ranges(buffer, range_and_faces.prefix, range_and_faces.list);

        for (auto& range : range_and_faces.list)
        {
            try
            {
                auto& r = std::get<0>(range);
                if (buffer.is_valid(r.first) and buffer.is_valid(r.last))
                {
                    auto replacement = parse_display_line(std::get<1>(range), context.context.faces());
                    replace_range(display_buffer, r.first, buffer.char_next(r.last),
                                  [&](DisplayLine& line, int beg_idx, int end_idx){
                                      auto it = line.erase(line.begin() + beg_idx, line.begin() + end_idx);
                                      for (auto& atom : replacement)
                                          it = ++line.insert(it, std::move(atom));
                                  });
                }
            }
            catch (runtime_error&)
            {}
        }
    }

    const String m_option_name;
};

HighlightPass parse_passes(StringView str)
{
    HighlightPass passes{};
    for (auto pass : str | split<StringView>('|'))
    {
        if (pass == "colorize")
            passes |= HighlightPass::Colorize;
        else if (pass == "move")
            passes |= HighlightPass::Move;
        else if (pass == "wrap")
            passes |= HighlightPass::Wrap;
        else
            throw runtime_error{format("invalid highlight pass: {}", pass)};
    }
    if (passes == HighlightPass{})
        throw runtime_error{"no passes specified"};

    return passes;
}

std::unique_ptr<Highlighter> create_highlighter_group(HighlighterParameters params, Highlighter*)
{
    static const ParameterDesc param_desc{
        { { "passes", { true, "" } } },
        ParameterDesc::Flags::SwitchesOnlyAtStart, 0, 0
    };
    ParametersParser parser{params, param_desc};
    HighlightPass passes = parse_passes(parser.get_switch("passes").value_or("colorize"));

    return std::make_unique<HighlighterGroup>(passes);
}

struct ReferenceHighlighter : Highlighter
{
    ReferenceHighlighter(HighlightPass passes, String name)
        : Highlighter{passes}, m_name{std::move(name)} {}

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        static const ParameterDesc param_desc{
            { { "passes", { true, "" } } },
            ParameterDesc::Flags::SwitchesOnlyAtStart, 1, 1
        };
        ParametersParser parser{params, param_desc};
        HighlightPass passes = parse_passes(parser.get_switch("passes").value_or("colorize"));
        return std::make_unique<ReferenceHighlighter>(passes, parser[0]);
    }

private:
    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange range) override
    {
        static Vector<std::pair<StringView, BufferRange>> running_refs;
        const std::pair<StringView, BufferRange> desc{m_name, range};
        if (contains(running_refs, desc))
            return write_to_debug_buffer(format("highlighting recursion detected with ref to {}", m_name));

        running_refs.push_back(desc);
        auto pop_desc = on_scope_end([] { running_refs.pop_back(); });

        try
        {
            DefinedHighlighters::instance().get_child(m_name).highlight(context, display_buffer, range);
        }
        catch (child_not_found&)
        {}
    }

    void do_compute_display_setup(HighlightContext context, DisplaySetup& setup) const override
    {
        try
        {
            DefinedHighlighters::instance().get_child(m_name).compute_display_setup(context, setup);
        }
        catch (child_not_found&)
        {}
    }

    const String m_name;
};

struct RegexMatch
{
    LineCount line;
    ByteCount begin;
    ByteCount end;
    StringView capture;

    BufferCoord begin_coord() const { return { line, begin }; }
    BufferCoord end_coord() const { return { line, end }; }
};
using RegexMatchList = Vector<RegexMatch, MemoryDomain::Highlight>;

void find_matches(const Buffer& buffer, RegexMatchList& matches, const Regex& regex, bool capture)
{
    capture = capture and regex.mark_count() > 0;
    for (auto line = 0_line, end = buffer.line_count(); line < end; ++line)
    {
        auto l = buffer[line];
        for (RegexIterator<const char*> it{l.begin(), l.end(), regex}, end{}; it != end; ++it)
        {
            auto& m = *it;
            ByteCount b = (int)(m[0].first - l.begin());
            ByteCount e = (int)(m[0].second - l.begin());
            auto cap = (capture and m[1].matched) ? StringView{m[1].first, m[1].second} : StringView{};
            matches.push_back({ line, b, e, cap });
        }
    }
}

void update_matches(const Buffer& buffer, ConstArrayView<LineModification> modifs,
                    RegexMatchList& matches, const Regex& regex, bool capture)
{
    // remove out of date matches and update line for others
    auto ins_pos = matches.begin();
    for (auto it = ins_pos; it != matches.end(); ++it)
    {
        auto modif_it = std::upper_bound(modifs.begin(), modifs.end(), it->line,
                                         [](const LineCount& l, const LineModification& c)
                                         { return l < c.old_line; });

        if (modif_it != modifs.begin())
        {
            auto& prev = *(modif_it-1);
            if (it->line < prev.old_line + prev.num_removed)
                continue; // match removed

            it->line += prev.diff();
        }

        kak_assert(buffer.is_valid(it->begin_coord()) or
                   buffer[it->line].length() == it->begin);
        kak_assert(buffer.is_valid(it->end_coord()) or
                   buffer[it->line].length() == it->end);

        if (ins_pos != it)
            *ins_pos = std::move(*it);
        ++ins_pos;
    }
    matches.erase(ins_pos, matches.end());
    size_t pivot = matches.size();

    // try to find new matches in each updated lines
    capture = capture and regex.mark_count() > 0;
    for (auto& modif : modifs)
    {
        for (auto line = modif.new_line; line < modif.new_line + modif.num_added; ++line)
        {
            auto l = buffer[line];
            for (RegexIterator<const char*> it{l.begin(), l.end(), regex}, end{}; it != end; ++it)
            {
                auto& m = *it;
                ByteCount b = (int)(m[0].first - l.begin());
                ByteCount e = (int)(m[0].second - l.begin());
                auto cap = (capture and m[1].matched) ? StringView{m[1].first, m[1].second} : StringView{};
                matches.push_back({ line, b, e, cap });
            }
        }
    }
    std::inplace_merge(matches.begin(), matches.begin() + pivot, matches.end(),
                       [](const RegexMatch& lhs, const RegexMatch& rhs) {
                           return lhs.begin_coord() < rhs.begin_coord();
                       });
}

struct RegionMatches
{
    RegexMatchList begin_matches;
    RegexMatchList end_matches;
    RegexMatchList recurse_matches;

    static bool compare_to_begin(const RegexMatch& lhs, BufferCoord rhs)
    {
        return lhs.begin_coord() < rhs;
    }

    RegexMatchList::const_iterator find_next_begin(BufferCoord pos) const
    {
        return std::lower_bound(begin_matches.begin(), begin_matches.end(),
                                pos, compare_to_begin);
    }

    RegexMatchList::const_iterator find_matching_end(BufferCoord beg_pos, Optional<StringView> capture) const
    {
        auto end_it = end_matches.begin();
        auto rec_it = recurse_matches.begin();
        int recurse_level = 0;
        while (true)
        {
            end_it = std::lower_bound(end_it, end_matches.end(), beg_pos,
                                      compare_to_begin);
            rec_it = std::lower_bound(rec_it, recurse_matches.end(), beg_pos,
                                      compare_to_begin);

            if (end_it == end_matches.end())
                return end_it;

            while (rec_it != recurse_matches.end() and
                   rec_it->end_coord() <= end_it->end_coord())
            {
                if (not capture or rec_it->capture == *capture)
                    ++recurse_level;
                ++rec_it;
            }

            if (not capture or *capture == end_it->capture)
            {
                if (recurse_level == 0)
                    return end_it;
                --recurse_level;
            }

            if (beg_pos != end_it->end_coord())
                beg_pos = end_it->end_coord();
            ++end_it;
        }
    }
};

struct RegionsHighlighter : public Highlighter
{
public:
    RegionsHighlighter()
        : Highlighter{HighlightPass::Colorize} {}

    void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange range) override
    {
        if (m_regions.empty())
            return;

        auto display_range = display_buffer.range();
        const auto& buffer = context.context.buffer();
        auto& regions = get_regions_for_range(buffer, range);

        auto begin = std::lower_bound(regions.begin(), regions.end(), display_range.begin,
                                      [](const Region& r, BufferCoord c) { return r.end < c; });
        auto end = std::lower_bound(begin, regions.end(), display_range.end,
                                    [](const Region& r, BufferCoord c) { return r.begin < c; });
        auto correct = [&](BufferCoord c) -> BufferCoord {
            if (not buffer.is_end(c) and buffer[c.line].length() == c.column)
                return {c.line+1, 0};
            return c;
        };

        auto default_region_it = m_regions.find(m_default_region);
        const bool apply_default = default_region_it != m_regions.end();

        auto last_begin = (begin == regions.begin()) ?
                             BufferCoord{0,0} : (begin-1)->end;
        kak_assert(begin <= end);
        for (; begin != end; ++begin)
        {
            if (apply_default and last_begin < begin->begin)
                apply_highlighter(context, display_buffer,
                                  correct(last_begin), correct(begin->begin),
                                  *default_region_it->value);

            auto it = m_regions.find(begin->region);
            if (it == m_regions.end())
                continue;
            apply_highlighter(context, display_buffer,
                              correct(begin->begin), correct(begin->end),
                              *it->value);
            last_begin = begin->end;
        }
        if (apply_default and last_begin < display_range.end)
            apply_highlighter(context, display_buffer,
                              correct(last_begin), range.end,
                              *default_region_it->value);
    }

    bool has_children() const override { return true; }

    Highlighter& get_child(StringView path) override
    {
        auto sep_it = find(path, '/');
        StringView id(path.begin(), sep_it);
        auto it = m_regions.find(id);
        if (it == m_regions.end())
            throw child_not_found(format("no such id: {}", id));
        if (sep_it == path.end())
            return *it->value;
        else
            return it->value->get_child({sep_it+1, path.end()});
    }

    void add_child(String name, std::unique_ptr<Highlighter>&& hl) override
    {
        if (not dynamic_cast<RegionHighlighter*>(hl.get()))
            throw runtime_error{"only region highlighter can be added as child of a regions highlighter"};
        if (m_regions.contains(name))
            throw runtime_error{format("duplicate id: '{}'", name)};

        std::unique_ptr<RegionHighlighter> region_hl{dynamic_cast<RegionHighlighter*>(hl.release())};
        if (region_hl->is_default())
        {
            if (not m_default_region.empty())
                throw runtime_error{"default region already defined"};
            m_default_region = name;
        }

        m_regions.insert({std::move(name), std::move(region_hl)});
        ++m_regions_timestamp;
    }

    void remove_child(StringView id) override
    {
        if (id == m_default_region)
            m_default_region = String{};

        m_regions.remove(id);
        ++m_regions_timestamp;
    }

    Completions complete_child(StringView path, ByteCount cursor_pos, bool group) const override
    {
        auto sep_it = find(path, '/');
        if (sep_it != path.end())
        {
            ByteCount offset = sep_it+1 - path.begin();
            Highlighter& hl = const_cast<RegionsHighlighter*>(this)->get_child({path.begin(), sep_it});
            return offset_pos(hl.complete_child(path.substr(offset), cursor_pos - offset, group), offset);
        }

        auto container = m_regions | transform(&decltype(m_regions)::Item::key);
        return { 0, 0, complete(path, cursor_pos, container) };
    }

    static std::unique_ptr<Highlighter> create(HighlighterParameters params, Highlighter*)
    {
        if (not params.empty())
            throw runtime_error{"unexpected parameters"};
        return std::make_unique<RegionsHighlighter>();
    }

    static bool is_regions(Highlighter* parent)
    {
        if (dynamic_cast<RegionsHighlighter*>(parent))
            return true;
        if (auto* region = dynamic_cast<RegionHighlighter*>(parent))
            return is_regions(&region->delegate());
        return false;
    }

    static std::unique_ptr<Highlighter> create_region(HighlighterParameters params, Highlighter* parent)
    {
        if (not is_regions(parent))
            throw runtime_error{"region highlighter can only be added to a regions parent"};

        static const ParameterDesc param_desc{
            { { "match-capture", { false, "" } }, { "recurse", { true, "" } } },
            ParameterDesc::Flags::SwitchesOnlyAtStart | ParameterDesc::Flags::IgnoreUnknownSwitches,
            3
        };

        ParametersParser parser{params, param_desc};

        const bool match_capture = (bool)parser.get_switch("match-capture");
        if (parser[0].empty() or parser[1].empty())
            throw runtime_error("begin and end must not be empty");

        const RegexCompileFlags flags = match_capture ?
            RegexCompileFlags::Optimize : RegexCompileFlags::NoSubs | RegexCompileFlags::Optimize;

        const auto& type = parser[2];
        auto& registry = HighlighterRegistry::instance();
        auto it = registry.find(type);
        if (it == registry.end())
            throw runtime_error(format("no such highlighter type: '{}'", type));

        Regex recurse;
        if (auto recurse_switch = parser.get_switch("recurse"))
            recurse = Regex{*recurse_switch, flags};

        auto delegate = it->value.factory(parser.positionals_from(3), nullptr);
        return std::make_unique<RegionHighlighter>(std::move(delegate), Regex{parser[0], flags}, Regex{parser[1], flags}, recurse, match_capture);
    }

    static std::unique_ptr<Highlighter> create_default_region(HighlighterParameters params, Highlighter* parent)
    {
        if (not is_regions(parent))
            throw runtime_error{"default-region highlighter can only be added to a regions parent"};

        static const ParameterDesc param_desc{ {}, ParameterDesc::Flags::SwitchesOnlyAtStart, 1 };
        ParametersParser parser{params, param_desc};

        auto delegate = HighlighterRegistry::instance()[parser[0]].factory(parser.positionals_from(1), nullptr);
        return std::make_unique<RegionHighlighter>(std::move(delegate));
    }

private:
    struct Region
    {
        BufferCoord begin;
        BufferCoord end;
        StringView region;
    };
    using RegionList = Vector<Region, MemoryDomain::Highlight>;

    struct Cache
    {
        size_t timestamp = 0;
        size_t regions_timestamp = 0;
        Vector<RegionMatches, MemoryDomain::Highlight> matches;
        HashMap<BufferRange, RegionList, MemoryDomain::Highlight> regions;
    };

    using RegionAndMatch = std::pair<size_t, RegexMatchList::const_iterator>;

    // find the begin closest to pos in all matches
    RegionAndMatch find_next_begin(const Cache& cache, BufferCoord pos) const
    {
        RegionAndMatch res{0, cache.matches[0].find_next_begin(pos)};
        for (size_t i = 1; i < cache.matches.size(); ++i)
        {
            const auto& matches = cache.matches[i];
            auto it = matches.find_next_begin(pos);
            if (it != matches.begin_matches.end() and
                (res.second == cache.matches[res.first].begin_matches.end() or
                 it->begin_coord() < res.second->begin_coord()))
                res = RegionAndMatch{i, it};
        }
        return res;
    }

    const RegionList& get_regions_for_range(const Buffer& buffer, BufferRange range)
    {
        Cache& cache = m_cache.get(buffer);
        const size_t buf_timestamp = buffer.timestamp();
        if (cache.timestamp != buf_timestamp or cache.regions_timestamp != m_regions_timestamp)
        {
            if (cache.timestamp == 0 or cache.regions_timestamp != m_regions_timestamp)
            {
                cache.matches.resize(m_regions.size());
                for (size_t i = 0; i < m_regions.size(); ++i)
                    cache.matches[i] = m_regions.item(i).value->find_matches(buffer);
            }
            else
            {
                auto modifs = compute_line_modifications(buffer, cache.timestamp);
                for (size_t i = 0; i < m_regions.size(); ++i)
                    m_regions.item(i).value->update_matches(buffer, modifs, cache.matches[i]);
            }

            cache.regions.clear();
        }

        auto it = cache.regions.find(range);
        if (it != cache.regions.end())
            return it->value;

        RegionList& regions = cache.regions[range];

        for (auto begin = find_next_begin(cache, range.begin),
                  end = RegionAndMatch{ 0, cache.matches[0].begin_matches.end() };
             begin != end; )
        {
            const RegionMatches& matches = cache.matches[begin.first];
            auto& region = m_regions.item(begin.first);
            auto beg_it = begin.second;
            auto end_it = matches.find_matching_end(beg_it->end_coord(),
                                                    region.value->match_capture() ? beg_it->capture : Optional<StringView>{});

            if (end_it == matches.end_matches.end() or end_it->end_coord() >= range.end)
            {
                regions.push_back({ {beg_it->line, beg_it->begin},
                                    range.end,
                                    region.key });
                break;
            }
            else
            {
                regions.push_back({ beg_it->begin_coord(),
                                   end_it->end_coord(),
                                   region.key });
                auto end_coord = end_it->end_coord();

                // With empty begin and end matches (for example if the regexes
                // are /"\K/ and /(?=")/), that case can happen, and would
                // result in an infinite loop.
                if (end_coord == beg_it->begin_coord())
                {
                    kak_assert(beg_it->begin_coord() == beg_it->end_coord() and
                               end_it->begin_coord() == end_it->end_coord());
                    ++end_coord.column;
                }
                begin = find_next_begin(cache, end_coord);
            }
        }
        cache.timestamp = buf_timestamp;
        cache.regions_timestamp = m_regions_timestamp;
        return regions;
    }

    struct RegionHighlighter : public Highlighter
    {
        RegionHighlighter(std::unique_ptr<Highlighter>&& delegate,
                          Regex begin, Regex end, Regex recurse,
                          bool match_capture)
            : Highlighter{delegate->passes()},
              m_delegate{std::move(delegate)},
              m_begin{std::move(begin)}, m_end{std::move(end)}, m_recurse{std::move(recurse)},
              m_match_capture{match_capture}
       {
       }

        RegionHighlighter(std::unique_ptr<Highlighter>&& delegate)
            : Highlighter{delegate->passes()}, m_delegate{std::move(delegate)}, m_default{true}
       {
       }

        bool has_children() const override
        {
            return m_delegate->has_children();
        }

        Highlighter& get_child(StringView path) override
        {
            return m_delegate->get_child(path);
        }

        void add_child(String name, std::unique_ptr<Highlighter>&& hl) override
        {
            return m_delegate->add_child(name, std::move(hl));
        }

        void remove_child(StringView id) override
        {
            return m_delegate->remove_child(id);
        }

        Completions complete_child(StringView path, ByteCount cursor_pos, bool group) const override
        {
            return m_delegate->complete_child(path, cursor_pos, group);
        }

        void fill_unique_ids(Vector<StringView>& unique_ids) const override
        {
            return m_delegate->fill_unique_ids(unique_ids);
        }

        void do_highlight(HighlightContext context, DisplayBuffer& display_buffer, BufferRange range) override
        {
            return m_delegate->highlight(context, display_buffer, range);
        }

        RegionMatches find_matches(const Buffer& buffer) const
        {
            RegionMatches res;
            if (m_default)
                return res;

            Kakoune::find_matches(buffer, res.begin_matches, m_begin, m_match_capture);
            Kakoune::find_matches(buffer, res.end_matches, m_end, m_match_capture);
            if (not m_recurse.empty())
                Kakoune::find_matches(buffer, res.recurse_matches, m_recurse, m_match_capture);
            return res;
        }

        void update_matches(const Buffer& buffer,
                            ConstArrayView<LineModification> modifs,
                            RegionMatches& matches) const
        {
            if (m_default)
                return;

            Kakoune::update_matches(buffer, modifs, matches.begin_matches, m_begin, m_match_capture);
            Kakoune::update_matches(buffer, modifs, matches.end_matches, m_end, m_match_capture);
            if (not m_recurse.empty())
                Kakoune::update_matches(buffer, modifs, matches.recurse_matches, m_recurse, m_match_capture);
        }

        bool match_capture() const { return m_match_capture; }
        bool is_default() const { return m_default; }

        Highlighter& delegate() { return *m_delegate; }

    private:
        std::unique_ptr<Highlighter> m_delegate;

        Regex m_begin;
        Regex m_end;
        Regex m_recurse;
        bool  m_match_capture = false;
        bool  m_default = false;
    };

    HashMap<String, std::unique_ptr<RegionHighlighter>, MemoryDomain::Highlight> m_regions;
    String m_default_region;

    size_t m_regions_timestamp = 0;
    BufferSideCache<Cache> m_cache;
};

void setup_builtin_highlighters(HighlighterGroup& group)
{
    group.add_child("tabulations"_str, std::make_unique<TabulationHighlighter>());
    group.add_child("unprintable"_str, make_highlighter(expand_unprintable));
    group.add_child("selections"_str,  make_highlighter(highlight_selections));
}

void register_highlighters()
{
    HighlighterRegistry& registry = HighlighterRegistry::instance();

    registry.insert({
        "number-lines",
        { LineNumbersHighlighter::create,
          "Display line numbers \n"
          "Parameters: -relative, -hlcursor, -separator <separator text>\n" } });
    registry.insert({
        "show-matching",
        { create_matching_char_highlighter,
          "Apply the MatchingChar face to the char matching the one under the cursor" } });
    registry.insert({
        "show-whitespaces",
        { ShowWhitespacesHighlighter::create,
          "Display whitespaces using symbols \n"
          "Parameters: -tab <separator> -tabpad <separator> -lf <separator> -spc <separator> -nbsp <separator>\n" } });
    registry.insert({
        "fill",
        { create_fill_highlighter,
          "Fill the whole highlighted range with the given face" } });
    registry.insert({
        "regex",
        { RegexHighlighter::create,
          "Parameters: <regex> <capture num>:<face> <capture num>:<face>...\n"
          "Highlights the matches for captures from the regex with the given faces" } });
    registry.insert({
        "dynregex",
        { create_dynamic_regex_highlighter,
          "Parameters: <expr> <capture num>:<face> <capture num>:<face>...\n"
          "Evaluate expression at every redraw to gather a regex" } });
    registry.insert({
        "group",
        { create_highlighter_group,
          "Parameters: [-passes <passes>]\n"
          "Creates a group that can contain other highlighters,\n"
          "<passes> is a flags(colorize|move|wrap) defaulting to colorize\n"
          "which specify what kind of highlighters can be put in the group" } });
    registry.insert({
        "flag-lines",
        { FlagLinesHighlighter::create,
          "Parameters: <face> <option name>\n"
          "Display flags specified in the line-spec option <option name> with <face>"} });
    registry.insert({
        "ranges",
        { RangesHighlighter::create,
          "Parameters: <option name>\n"
          "Use the range-specs option given as parameter to highlight buffer\n"
          "each spec is interpreted as a face to apply to the range\n" } });
    registry.insert({
        "replace-ranges",
        { ReplaceRangesHighlighter::create,
          "Parameters: <option name>\n"
          "Use the range-specs option given as parameter to highlight buffer\n"
          "each spec is interpreted as a display line to display in place of the range\n" } });
    registry.insert({
        "line",
        { create_line_highlighter,
          "Parameters: <value string> <face>\n"
          "Highlight the line given by evaluating <value string> with <face>" } });
    registry.insert({
        "column",
        { create_column_highlighter,
          "Parameters: <value string> <face>\n"
          "Highlight the column given by evaluating <value string> with <face>" } });
    registry.insert({
        "wrap",
        { WrapHighlighter::create,
          "Parameters: [-word] [-indent] [-width <max_width>] [-marker <marker_text>]\n"
          "Wrap lines to window width, or max_width if given and window is wider,\n"
          "wrap at word boundaries instead of codepoint boundaries if -word is given\n"
          "insert marker_text at start of wrapped lines if given\n"
          "preserve line indent in wrapped parts if -indent is given\n"} });
    registry.insert({
        "ref",
        { ReferenceHighlighter::create,
          "Parameters: [-passes <passes>] <path>\n"
          "Reference the highlighter at <path> in shared highlighters\n"
          "<passes> is a flags(colorize|move|wrap) defaulting to colorize\n"
          "which specify what kind of highlighters can be referenced" } });
    registry.insert({
        "regions",
        { RegionsHighlighter::create,
          "Parameters: None"
          "Holds child region highlighters and segments the buffer in ranges based on those regions\n"
          "definitions. The regions highlighter finds the next region to start by finding which\n"
          "of its child region has the leftmost starting point from current position. In between\n"
          "regions, the default-region child highlighter is applied (if such a child exists)" } });
    registry.insert({
        "region",
        { RegionsHighlighter::create_region,
          "Parameters:  [-match-capture] [-recurse <recurse>] <opening> <closing> <type> <params>..."
          "Define a region for a regions highlighter, and apply the given delegate\n"
          "highlighter as defined by <type> and eventual <params>...\n"
          "The region starts at <begin> match and ends at the first <end>\n"
          "If -recurse is specified, then the region ends at the first <end> that\n"
          "does not close a <recurse> match.\n"
          "If -match-capture is specified, then regions end/recurse matches must have\n"
          "the same \\1 capture content as the begin match to be considered"} });
    registry.insert({
        "default-region",
        { RegionsHighlighter::create_default_region,
          "Parameters: <delegate_type> <delegate_params>...\n"
          "Define the default region of a regions highlighter" } });
}

}