add(header): header with configurable title

src/widget/Header.zig

@@ -0,0 +1,103 @@
+//! Header widget, which shows the name of the website and the main navigation entries
+const std = @import("std");
+const vaxis = @import("vaxis");
+
+const widget = @import("../widget.zig");
+
+const Event = widget.Event;
+
+allocator: std.mem.Allocator = undefined,
+unicode: *const vaxis.Unicode = undefined,
+title: ?[]const u8 = undefined,
+view: ?vaxis.widgets.View = undefined,
+
+pub fn init(allocator: std.mem.Allocator, unicode: *const vaxis.Unicode) !@This() {
+    return .{
+        .allocator = allocator,
+        .unicode = unicode,
+        .title = null,
+        .view = null,
+    };
+}
+
+pub fn deinit(this: *@This()) void {
+    if (this.view) |*view| {
+        view.*.deinit();
+    }
+    if (this.title) |*title| {
+        this.allocator.free(title.*);
+    }
+    this.* = undefined;
+}
+
+fn fillView(this: *@This()) void {
+    this.view.?.clear();
+
+    const msg = "Yves Biener";
+    for (msg, 0..) |_, i| {
+        const cell: vaxis.Cell = .{
+            // each cell takes a _grapheme_ as opposed to a single
+            // codepoint. This allows Vaxis to handle emoji properly,
+            // particularly with terminals that the Unicode Core extension
+            // (IE Mode 2027)
+            .char = .{ .grapheme = msg[i .. i + 1] },
+            .style = .{
+                .fg = .{ .index = 6 },
+                .bold = true,
+            },
+        };
+        this.view.?.writeCell(i, 0, cell);
+    }
+
+    if (this.title) |title| {
+        // TODO: this could be a static string on the heap (due to the size of `513`)
+        std.log.debug("this.title := {s}({d}) - width: {d}", .{ title, title.len, this.view.?.screen.width });
+        for (title, 0.., this.view.?.screen.width / 2..) |_, i, col| {
+            const cell: vaxis.Cell = .{
+                .char = .{ .grapheme = title[i .. i + 1] },
+                .style = .{
+                    .ul_style = .single,
+                },
+            };
+            this.view.?.writeCell(col, 0, cell);
+        }
+    }
+}
+
+/// Update loop for a given widget to react to the provided `Event`. It may
+/// change its internal state, update variables, react to user input, etc.
+pub fn update(this: *@This(), event: Event) void {
+    switch (event) {
+        .winsize => |ws| {
+            if (this.view) |*view| {
+                if (ws.rows != view.screen.width) {
+                    view.*.deinit();
+                    this.view = vaxis.widgets.View.init(this.allocator, this.unicode, .{ .width = ws.rows, .height = ws.cols }) catch @panic("OOM");
+                    this.fillView();
+                }
+            } else {
+                this.view = vaxis.widgets.View.init(this.allocator, this.unicode, .{ .width = ws.rows, .height = ws.cols }) catch @panic("OOM");
+                this.fillView();
+            }
+        },
+        .title => |title| {
+            if (this.title) |*t| {
+                this.allocator.free(t.*);
+            }
+            const t = this.allocator.alloc(u8, title.len) catch @panic("OOM");
+            @memcpy(t, title);
+            this.title = t;
+            this.fillView();
+        },
+        else => {},
+    }
+}
+
+/// Draw a given widget using the provided `vaxis.Window`. The window controls
+/// the dimension one widget may take on the screen. The widget itself has no
+/// control over this.
+pub fn draw(this: *@This(), win: vaxis.Window) void {
+    if (this.view) |*view| {
+        view.*.draw(win, .{});
+    }
+}