fix: merge selections when collapsing cursors

closes #318

src/buffer/Cursor.zig

@@ -245,3 +245,9 @@ pub fn nudge_delete(self: *Self, nudge: Selection) bool {
     self.row -= nudge.end.row - nudge.begin.row;
     return true;
 }
+
+pub fn within(self: *const Self, sel_: Selection) bool {
+    var sel = sel_;
+    sel.normalize();
+    return !sel.begin.right_of(self.*) and sel.end.right_of(self.*);
+}

src/buffer/Selection.zig

@@ -85,3 +85,53 @@ pub fn nudge_delete(self: *Self, nudge: Self) bool {
         return false;
     return self.end.nudge_delete(nudge);
 }
+
+pub fn merge(self: *Self, other_: Self) bool {
+    var other = other_;
+    other.normalize();
+    if (self.is_reversed()) {
+        var this = self.*;
+        this.normalize();
+        if (this.merge_normal(other)) {
+            self.begin = this.end;
+            self.end = this.begin;
+            return true;
+        }
+        return false;
+    }
+    return self.merge_normal(other);
+}
+
+fn merge_normal(self: *Self, other: Self) bool {
+    var merged = false;
+    if (self.begin.within(other)) {
+        self.begin = other.begin;
+        merged = true;
+    }
+    if (self.end.within(other)) {
+        self.end = other.end;
+        merged = true;
+    }
+    return merged or
+        (other.begin.right_of(self.begin) and
+            self.end.right_of(other.end));
+}
+
+pub fn expand(self: *Self, other_: Self) void {
+    var other = other_;
+    other.normalize();
+    if (self.is_reversed()) {
+        var this = self.*;
+        this.normalize();
+        this.expand_normal(other);
+        self.begin = this.end;
+        self.end = this.begin;
+    } else self.expand_normal(other);
+}
+
+fn expand_normal(self: *Self, other: Self) void {
+    if (self.begin.right_of(other.begin))
+        self.begin = other.begin;
+    if (other.end.right_of(self.end))
+        self.end = other.end;
+}

src/tui/editor.zig

@@ -242,6 +242,16 @@ pub const CurSel = struct {
                 return false;
         return self.cursor.nudge_delete(nudge);
     }
+
+    fn merge(self: *Self, other: Selection) bool {
+        if (self.selection) |*sel_| {
+            if (sel_.merge(other)) {
+                self.cursor = sel_.end;
+                return true;
+            }
+        }
+        return self.cursor.within(other);
+    }
 };
 
 pub const Diagnostic = struct {
@@ -1827,10 +1837,26 @@ pub const Editor = struct {
         var old = self.cursels;
         defer old.deinit(self.allocator);
         self.cursels = CurSel.List.initCapacity(self.allocator, old.items.len) catch return;
-        for (old.items[0 .. old.items.len - 1], 0..) |*a_, i| if (a_.*) |*a| {
+        var a_idx = old.items.len - 1;
-            for (old.items[i + 1 ..], i + 1..) |*b_, j| if (b_.*) |*b| {
+        while (a_idx > 0) : (a_idx -= 1) if (old.items[a_idx]) |*a| {
-                if (a.cursor.eql(b.cursor))
+            var b_idx = a_idx - 1;
-                    old.items[j] = null;
+            while (true) : ({
+                if (b_idx == 0) break else b_idx -= 1;
+            }) if (old.items[b_idx]) |*b| {
+                const b_cursor = b.cursor;
+                if (b.selection) |b_sel| {
+                    if (a.merge(b_sel)) {
+                        old.items[b_idx] = null;
+                        continue;
+                    }
+                }
+                if (a.selection) |*a_sel| if (b_cursor.within(a_sel.*)) {
+                    if (b.selection) |b_sel| a_sel.expand(b_sel);
+                    old.items[b_idx] = null;
+                    continue;
+                };
+                if (a.cursor.eql(b_cursor))
+                    old.items[b_idx] = null;
             };
         };
         for (old.items) |*item_| if (item_.*) |*item| {
@@ -2402,6 +2428,7 @@ pub const Editor = struct {
         self.selection_mode = .char;
         try self.send_editor_jump_source();
         primary.cursor.move_abs(root, &self.view, @intCast(y), @intCast(x), self.metrics) catch return;
+        self.collapse_cursors();
         self.clamp_mouse();
         try self.send_editor_jump_destination();
         if (self.jump_mode) try self.goto_definition(.{});
@@ -2415,6 +2442,7 @@ pub const Editor = struct {
         primary.cursor.move_abs(root, &self.view, @intCast(y), @intCast(x), self.metrics) catch return;
         _ = try self.select_word_at_cursor(primary);
         self.selection_drag_initial = primary.selection;
+        self.collapse_cursors();
         self.clamp_mouse();
     }
 
@@ -2426,6 +2454,7 @@ pub const Editor = struct {
         primary.cursor.move_abs(root, &self.view, @intCast(y), @intCast(x), self.metrics) catch return;
         try self.select_line_at_cursor(root, primary, .exclude_eol);
         self.selection_drag_initial = primary.selection;
+        self.collapse_cursors();
         self.clamp_mouse();
     }
 
@@ -2463,6 +2492,7 @@ pub const Editor = struct {
         }
         primary.cursor = sel.end;
         primary.check_selection(root, self.metrics);
+        self.collapse_cursors();
         self.clamp_mouse();
     }