Selectors: add select_surrounding to select blocks

Alt-a followed by []()<>{}bB selects the block surrounding current
selection end.

Alt-i is similar but selects only the inside of the block.

src/main.cc

@@ -708,6 +708,30 @@ void do_join(Window& window, int count)
     window.move_cursor({0, -1});
 }
 
+template<bool inside>
+void do_select_surrounding(Window& window, int count)
+{
+    char id = getch();
+
+    static const std::unordered_map<char, std::pair<char, char>> id_to_matching =
+    {
+       { '(', { '(', ')' } },
+       { ')', { '(', ')' } },
+       { 'b', { '(', ')' } },
+       { '{', { '{', '}' } },
+       { '}', { '{', '}' } },
+       { 'B', { '{', '}' } },
+       { '[', { '[', ']' } },
+       { ']', { '[', ']' } },
+       { '<', { '<', '>' } },
+       { '>', { '<', '>' } }
+    };
+
+    auto matching = id_to_matching.find(id);
+    if (matching != id_to_matching.end())
+        window.select(std::bind(select_surrounding, _1, matching->second, inside));
+}
+
 std::unordered_map<Key, std::function<void (Window& window, int count)>> keymap =
 {
     { { Key::Modifiers::None, 'h' }, [](Window& window, int count) { window.move_cursor(DisplayCoord(0, -std::max(count,1))); } },
@@ -767,6 +791,9 @@ std::unordered_map<Key, std::function<void (Window& window, int count)>> keymap
     { { Key::Modifiers::None, 'u' }, [](Window& window, int count) { do { if (not window.undo()) { print_status("nothing left to undo"); break; } } while(--count > 0); } },
     { { Key::Modifiers::None, 'U' }, [](Window& window, int count) { do { if (not window.redo()) { print_status("nothing left to redo"); break; } } while(--count > 0); } },
 
+    { { Key::Modifiers::Alt,  'i' }, do_select_surrounding<true> },
+    { { Key::Modifiers::Alt,  'a' }, do_select_surrounding<false> },
+
     { { Key::Modifiers::Alt, 't' }, [](Window& window, int count) { window.select(std::bind(select_to_reverse, _1, getch(), count, false)); } },
     { { Key::Modifiers::Alt, 'f' }, [](Window& window, int count) { window.select(std::bind(select_to_reverse, _1, getch(), count, true)); } },
     { { Key::Modifiers::Alt, 'T' }, [](Window& window, int count) { window.select(std::bind(select_to_reverse, _1, getch(), count, false), true); } },

src/selectors.cc

@@ -242,6 +242,55 @@ Selection select_matching(const BufferIterator& cursor)
     return Selection(cursor, cursor);
 }
 
+Selection select_surrounding(const BufferIterator& cursor,
+                             const std::pair<char, char>& matching,
+                             bool inside)
+{
+    int level = 0;
+    BufferIterator first = cursor;
+    while (not first.is_begin())
+    {
+        if (*first == matching.second)
+            ++level;
+        else if (*first == matching.first)
+        {
+            if (level == 0)
+                break;
+            else
+                --level;
+        }
+        --first;
+    }
+    if (level != 0 or *first != matching.first)
+        return Selection(cursor, cursor);
+
+    level = 0;
+    BufferIterator last = first + 1;
+    while (not last.is_end())
+    {
+        if (*last == matching.first)
+            ++level;
+        else if (*last == matching.second)
+        {
+            if (level == 0)
+                break;
+            else
+                --level;
+        }
+        ++last;
+    }
+    if (level != 0 or *last != matching.second)
+        return Selection(cursor, cursor);
+
+    if (inside)
+    {
+        ++first;
+        if (first != last)
+            --last;
+    }
+    return Selection(first, last);
+}
+
 Selection select_to(const BufferIterator& cursor, char c, int count, bool inclusive)
 {
     BufferIterator end = cursor;

src/selectors.hh

@@ -14,6 +14,9 @@ Selection select_to_next_WORD_end(const BufferIterator& cursor);
 Selection select_to_previous_WORD(const BufferIterator& cursor);
 Selection select_line(const BufferIterator& cursor);
 Selection select_matching(const BufferIterator& cursor);
+Selection select_surrounding(const BufferIterator& cursor,
+                             const std::pair<char, char>& matching,
+                              bool inside);
 
 Selection select_to(const BufferIterator& cursor, char c, int count, bool inclusive);
 Selection select_to_reverse(const BufferIterator& cursor, char c, int count, bool inclusive);