feat: adds gap_buffer.zig for TextInput (#6)

Use a gap buffer for the `TextInput` widget instead of an `ArrayList`.

build.zig

@@ -14,6 +14,10 @@ pub fn build(b: *std.Build) void {
         .optimize = optimize,
         .target = target,
     });
+    const gap_buffer_dep = b.dependency("gap_buffer", .{
+        .optimize = optimize,
+        .target = target,
+    });
 
     // Module
     const vaxis_mod = b.addModule("vaxis", .{
@@ -23,6 +27,7 @@ pub fn build(b: *std.Build) void {
     });
     vaxis_mod.addImport("ziglyph", ziglyph_dep.module("ziglyph"));
     vaxis_mod.addImport("zigimg", zigimg_dep.module("zigimg"));
+    vaxis_mod.addImport("gap_buffer", gap_buffer_dep.module("gap_buffer"));
 
     // Examples
     const example_step = b.step("example", "Run examples");
@@ -49,6 +54,7 @@ pub fn build(b: *std.Build) void {
     });
     tests.root_module.addImport("ziglyph", ziglyph_dep.module("ziglyph"));
     tests.root_module.addImport("zigimg", zigimg_dep.module("zigimg"));
+    tests.root_module.addImport("gap_buffer", gap_buffer_dep.module("gap_buffer"));
 
     const tests_run = b.addRunArtifact(tests);
     b.installArtifact(tests);

build.zig.zon

@@ -11,5 +11,9 @@
             .url = "https://github.com/rockorager/zigimg/archive/19a49a7.tar.gz",
             .hash = "1220ebfa8587cfd644995fc08e218dbb3ebd7344fb8e129ff02bc5a6d52a2325370d",
         },
+        .gap_buffer = .{
+            .url = "https://github.com/ryleelyman/GapBuffer.zig/archive/6a746497d5a2494026d0f471e42556f1f153f153.tar.gz",
+            .hash = "12205354d9903e773f9d934dcfe756b0b5ffd895571ad631ab86ebc1aebba074dd82",
+        },
     },
 }

src/widgets/TextInput.zig

@@ -3,6 +3,7 @@ const Key = @import("../Key.zig");
 const Cell = @import("../Cell.zig");
 const Window = @import("../Window.zig");
 const GraphemeIterator = @import("ziglyph").GraphemeIterator;
+const GapBuffer = @import("gap_buffer").GapBuffer;
 
 const log = std.log.scoped(.text_input);
 
@@ -16,15 +17,11 @@ const Event = union(enum) {
 // Index of our cursor
 cursor_idx: usize = 0,
 grapheme_count: usize = 0,
-
+buf: GapBuffer(u8),
-// TODO: an ArrayList is not great for this. orderedRemove is O(n) and we can
-// only remove one byte at a time. Make a bespoke ArrayList which allows removal
-// of a slice at a time, or truncating even would be nice
-buf: std.ArrayList(u8),
 
 pub fn init(alloc: std.mem.Allocator) TextInput {
     return TextInput{
-        .buf = std.ArrayList(u8).init(alloc),
+        .buf = GapBuffer(u8).init(alloc),
     };
 }
 
@@ -37,10 +34,10 @@ pub fn update(self: *TextInput, event: Event) !void {
         .key_press => |key| {
             if (key.matches(Key.backspace, .{})) {
                 if (self.cursor_idx == 0) return;
-                self.deleteBeforeCursor();
+                try self.deleteBeforeCursor();
             } else if (key.matches(Key.delete, .{}) or key.matches('d', .{ .ctrl = true })) {
                 if (self.cursor_idx == self.grapheme_count) return;
-                self.deleteAtCursor();
+                try self.deleteAtCursor();
             } else if (key.matches(Key.left, .{}) or key.matches('b', .{ .ctrl = true })) {
                 if (self.cursor_idx > 0) self.cursor_idx -= 1;
             } else if (key.matches(Key.right, .{}) or key.matches('f', .{ .ctrl = true })) {
@@ -50,15 +47,11 @@ pub fn update(self: *TextInput, event: Event) !void {
             } else if (key.matches('e', .{ .ctrl = true })) {
                 self.cursor_idx = self.grapheme_count;
             } else if (key.matches('k', .{ .ctrl = true })) {
-                while (self.cursor_idx < self.grapheme_count) {
+                try self.deleteToEnd();
-                    self.deleteAtCursor();
-                }
             } else if (key.matches('u', .{ .ctrl = true })) {
-                while (self.cursor_idx > 0) {
+                try self.deleteToStart();
-                    self.deleteBeforeCursor();
-                }
             } else if (key.text) |text| {
-                try self.buf.insertSlice(self.byteOffsetToCursor(), text);
+                try self.buf.insertSliceBefore(self.byteOffsetToCursor(), text);
                 self.cursor_idx += 1;
                 self.grapheme_count += 1;
             }
@@ -67,11 +60,13 @@ pub fn update(self: *TextInput, event: Event) !void {
 }
 
 pub fn draw(self: *TextInput, win: Window) void {
-    var iter = GraphemeIterator.init(self.buf.items);
+    // assumption!! the gap is never within a grapheme
+    // one way to _ensure_ this is to move the gap... but that's a cost we probably don't want to pay.
+    var first_iter = GraphemeIterator.init(self.buf.items);
     var col: usize = 0;
     var i: usize = 0;
     var cursor_idx: usize = 0;
-    while (iter.next()) |grapheme| {
+    while (first_iter.next()) |grapheme| {
         const g = grapheme.slice(self.buf.items);
         const w = win.gwidth(g);
         win.writeCell(col, 0, .{
@@ -84,11 +79,30 @@ pub fn draw(self: *TextInput, win: Window) void {
         i += 1;
         if (i == self.cursor_idx) cursor_idx = col;
     }
+    const second_half = self.buf.secondHalf();
+    var second_iter = GraphemeIterator.init(second_half);
+    while (second_iter.next()) |grapheme| {
+        const g = grapheme.slice(second_half);
+        const w = win.gwidth(g);
+        win.writeCell(col, 0, .{
+            .char = .{
+                .grapheme = g,
+                .width = w,
+            },
+        });
+        col += w;
+        i += 1;
+        if (i == self.cursor_idx) cursor_idx = col;
+    }
     win.showCursor(cursor_idx, 0);
 }
 
 // returns the number of bytes before the cursor
+// (since GapBuffers are strictly speaking not contiguous, this is a number in 0..realLength()
+// which would need to be fed to realIndex() to get an actual offset into self.buf.items.ptr)
 fn byteOffsetToCursor(self: TextInput) usize {
+    // assumption! the gap is never in the middle of a grapheme
+    // one way to _ensure_ this is to move the gap... but that's a cost we probably don't want to pay.
     var iter = GraphemeIterator.init(self.buf.items);
     var offset: usize = 0;
     var i: usize = 0;
@@ -96,20 +110,52 @@ fn byteOffsetToCursor(self: TextInput) usize {
         if (i == self.cursor_idx) break;
         offset += grapheme.len;
         i += 1;
+    } else {
+        var second_iter = GraphemeIterator.init(self.buf.secondHalf());
+        while (second_iter.next()) |grapheme| {
+            if (i == self.cursor_idx) break;
+            offset += grapheme.len;
+            i += 1;
+        }
     }
     return offset;
 }
 
-fn deleteBeforeCursor(self: *TextInput) void {
+fn deleteToEnd(self: *TextInput) !void {
+    self.cursor_idx += 1;
+    const offset = self.byteOffsetToCursor();
+    try self.buf.replaceRangeAfter(offset, self.buf.realLength(), &.{});
+    self.grapheme_count = self.cursor_idx;
+    self.cursor_idx -= 1;
+}
+
+fn deleteToStart(self: *TextInput) !void {
+    const offset = self.byteOffsetToCursor();
+    try self.buf.replaceRangeBefore(0, offset, &.{});
+    self.grapheme_count -= self.cursor_idx;
+    self.cursor_idx = 0;
+}
+
+fn deleteBeforeCursor(self: *TextInput) !void {
+    // assumption! the gap is never in the middle of a grapheme
+    // one way to _ensure_ this is to move the gap... but that's a cost we probably don't want to pay.
     var iter = GraphemeIterator.init(self.buf.items);
     var offset: usize = 0;
     var i: usize = 1;
     while (iter.next()) |grapheme| {
         if (i == self.cursor_idx) {
-            var j: usize = 0;
+            try self.buf.replaceRangeBefore(offset, grapheme.len, &.{});
-            while (j < grapheme.len) : (j += 1) {
+            self.cursor_idx -= 1;
-                _ = self.buf.orderedRemove(offset);
+            self.grapheme_count -= 1;
+            return;
         }
+        offset += grapheme.len;
+        i += 1;
+    } else {
+        var second_iter = GraphemeIterator.init(self.buf.secondHalf());
+        while (second_iter.next()) |grapheme| {
+            if (i == self.cursor_idx) {
+                try self.buf.replaceRangeBefore(offset, grapheme.len, &.{});
                 self.cursor_idx -= 1;
                 self.grapheme_count -= 1;
                 return;
@@ -117,22 +163,46 @@ fn deleteBeforeCursor(self: *TextInput) void {
             offset += grapheme.len;
             i += 1;
         }
+    }
 }
 
-fn deleteAtCursor(self: *TextInput) void {
+fn deleteAtCursor(self: *TextInput) !void {
+    // assumption! the gap is never in the middle of a grapheme
+    // one way to _ensure_ this is to move the gap... but that's a cost we probably don't want to pay.
     var iter = GraphemeIterator.init(self.buf.items);
     var offset: usize = 0;
     var i: usize = 1;
     while (iter.next()) |grapheme| {
         if (i == self.cursor_idx + 1) {
-            var j: usize = 0;
+            try self.buf.replaceRangeAfter(offset, grapheme.len, &.{});
-            while (j < grapheme.len) : (j += 1) {
+            self.grapheme_count -= 1;
-                _ = self.buf.orderedRemove(offset);
+            return;
         }
+        offset += grapheme.len;
+        i += 1;
+    } else {
+        var second_iter = GraphemeIterator.init(self.buf.secondHalf());
+        while (second_iter.next()) |grapheme| {
+            if (i == self.cursor_idx + 1) {
+                try self.buf.replaceRangeAfter(offset, grapheme.len, &.{});
                 self.grapheme_count -= 1;
                 return;
             }
             offset += grapheme.len;
             i += 1;
         }
+    }
+}
+
+test "assertion" {
+    const astronaut = "👩‍🚀";
+    const astronaut_emoji: Key = .{
+        .text = astronaut,
+        .codepoint = try std.unicode.utf8Decode(astronaut[0..4]),
+    };
+    var input = TextInput.init(std.testing.allocator);
+    defer input.deinit();
+    for (0..6) |_| {
+        try input.update(.{ .key_press = astronaut_emoji });
+    }
 }