widgets: add CodeView widget

CodeView widget allows viewing code in a more visually pleasing manner.
It combines LineNumbers widget to provide line numbers on the side.
The CodeView widget allows you to optionally highlight a specific line
and show indentation guidelines.

It is not intended to be a fully fledged editor, but rather for showing
code snippets to a user.

While it is not a fully fledged editor, this widget's code can give you
a good starting point.

src/widgets.zig

@@ -9,3 +9,4 @@ pub const nvim = @import("widgets/nvim.zig");
 pub const ScrollView = @import("widgets/ScrollView.zig");
 pub const LineNumbers = @import("widgets/LineNumbers.zig");
 pub const TextView = @import("widgets/TextView.zig");
+pub const CodeView = @import("widgets/CodeView.zig");

src/widgets/CodeView.zig

@@ -0,0 +1,112 @@
+const std = @import("std");
+const vaxis = @import("../main.zig");
+const ScrollView = vaxis.widgets.ScrollView;
+const LineNumbers = vaxis.widgets.LineNumbers;
+
+pub const DrawOptions = struct {
+    highlighted_line: usize = 0,
+    draw_line_numbers: bool = true,
+    indentation: usize = 0,
+};
+
+pub const Buffer = vaxis.widgets.TextView.Buffer;
+
+scroll_view: ScrollView = .{ .vertical_scrollbar = null },
+highlighted_style: vaxis.Style = .{ .bg = .{ .index = 0 } },
+indentation_cell: vaxis.Cell = .{
+    .char = .{
+        .grapheme = "┆",
+        .width = 1,
+    },
+    .style = .{ .dim = true },
+},
+
+pub fn input(self: *@This(), key: vaxis.Key) void {
+    self.scroll_view.input(key);
+}
+
+pub fn draw(self: *@This(), win: vaxis.Window, buffer: Buffer, opts: DrawOptions) void {
+    const pad_left: usize = if (opts.draw_line_numbers) LineNumbers.numDigits(buffer.rows) +| 1 else 0;
+    self.scroll_view.draw(win, .{
+        .cols = buffer.cols + pad_left,
+        .rows = buffer.rows,
+    });
+    if (opts.draw_line_numbers) {
+        var nl: LineNumbers = .{
+            .highlighted_line = opts.highlighted_line,
+            .num_lines = buffer.rows +| 1,
+        };
+        nl.draw(win.child(.{
+            .x_off = 0,
+            .y_off = 0,
+            .width = .{ .limit = pad_left },
+            .height = .{ .limit = win.height },
+        }), self.scroll_view.scroll.y);
+    }
+    self.drawCode(win.child(.{ .x_off = pad_left }), buffer, opts);
+}
+
+fn drawCode(self: *@This(), win: vaxis.Window, buffer: Buffer, opts: DrawOptions) void {
+    const Pos = struct { x: usize = 0, y: usize = 0 };
+    var pos: Pos = .{};
+    var byte_index: usize = 0;
+    var is_indentation = true;
+    const bounds = self.scroll_view.bounds(win);
+    for (buffer.grapheme.items(.len), buffer.grapheme.items(.offset), 0..) |g_len, g_offset, index| {
+        if (bounds.above(pos.y)) {
+            break;
+        }
+
+        const cluster = buffer.content.items[g_offset..][0..g_len];
+        defer byte_index += cluster.len;
+
+        if (std.mem.eql(u8, cluster, "\n")) {
+            if (index == buffer.grapheme.len - 1) {
+                break;
+            }
+            pos.y += 1;
+            pos.x = 0;
+            is_indentation = true;
+            continue;
+        } else if (bounds.below(pos.y)) {
+            continue;
+        }
+
+        const highlighted_line = pos.y +| 1 == opts.highlighted_line;
+        var style: vaxis.Style = if (highlighted_line) self.highlighted_style else .{};
+
+        if (buffer.style_map.get(byte_index)) |meta| {
+            const tmp = style.bg;
+            style = buffer.style_list.items[meta];
+            style.bg = tmp;
+        }
+
+        const width = win.gwidth(cluster);
+        defer pos.x +|= width;
+
+        if (!bounds.colInside(pos.x)) {
+            continue;
+        }
+
+        if (opts.indentation > 0 and !std.mem.eql(u8, cluster, " ")) {
+            is_indentation = false;
+        }
+
+        if (is_indentation and opts.indentation > 0 and pos.x % opts.indentation == 0) {
+            var cell = self.indentation_cell;
+            cell.style.bg = style.bg;
+            self.scroll_view.writeCell(win, pos.x, pos.y, cell);
+        } else {
+            self.scroll_view.writeCell(win, pos.x, pos.y, .{
+                .char = .{ .grapheme = cluster, .width = width },
+                .style = style,
+            });
+        }
+
+        if (highlighted_line) {
+            for (pos.x +| width..bounds.x2) |x| {
+                self.scroll_view.writeCell(win, x, pos.y, .{ .style = style });
+            }
+        }
+    }
+}