Add datetime components 196-215; Kit.At; inert stepper arrows

Calendars, date and time inputs, pickers, clocks, timers, a sun dial,
a season wheel, an agenda and a day schedule. Kit.At rebuilds at a
moment (relative times, midnight). Stepper and NumberInput arrows stop
under Inert. DateInput parks a popup focus as its own.

datetime/dateinput.go

@@ -0,0 +1,77 @@
+package datetime
+
+import (
+	"log/slog"
+	"time"
+
+	"github.com/egoist/mygo/ui"
+
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/icon"
+	"git.zacharyzhang.com/ZacharyZhang-NY/8bitMyGoUI/pixel"
+)
+
+type DateInputOptions struct {
+	Disabled bool
+}
+
+type DateInputResult struct {
+	Element *ui.Element
+	Changed bool
+}
+
+type dateKey struct{}
+
+// popping is whether the calendar is open and focused.
+type popping struct{ open, held bool }
+
+// DateInput shows YYYY-MM-DD; a press opens a calendar under it.
+func DateInput(c *ui.Context, text string, date *time.Time, o DateInputOptions) DateInputResult {
+	k := pixel.K(c)
+	old := *date
+	shell, base, st := pixel.Shell(c, func() *ui.Element {
+		return ui.ButtonBase(c).Role(ui.RolePopUpButton).Label(text).Disabled(o.Disabled)
+	})
+	pop := ui.Local(base, dateKey{}, func() popping { return popping{} })
+	open, was := &pop.open, pop.open
+	if base.Clicked() {
+		*open = !*open
+	}
+	// Closing with the field, its focus parks as the field's.
+	if o.Disabled || pixel.Current(c).Inert {
+		if *open && pop.held {
+			base.Focus()
+			pixel.Park(c, base, true)
+		}
+		*open = false
+	}
+	shown := date.Format("2006-01-02")
+	base.Description(shown)
+	shell.Size(k.D(pixel.Measure(shown)+24), k.D(pixel.LineHeight+6)).Draw(func(p *ui.Painter, r ui.Rect) {
+		g := k.Canvas(p, r)
+		g.Frame(0, 0, g.W, g.H, pixel.Sunken, pixel.Well)
+		g.Text(4, 3, shown, pixel.Ink, 1)
+		g.Sprite(g.W-icon.Calendar.W-4, (g.H-icon.Calendar.H)/2, icon.Calendar, 0, pixel.Faint, 1)
+		g.Finish(st)
+	})
+	ui.PopoverBase(c, base, open, func(panel *ui.Element) {
+		panel.Padding(k.D(5)).Draw(func(p *ui.Painter, r ui.Rect) {
+			g := k.Canvas(p, r)
+			g.Frame(0, 0, g.W, g.H, pixel.Window, pixel.Face)
+		}).Children(func() {
+			e, grid, picked := month(c, text, date, false, true, func(d time.Time) look { return look{chosen: sameDay(d, *date)} })
+			// The grid holds focus before its chain links.
+			pop.held = grid.Focused() || e.FocusWithin()
+			if picked {
+				*open = false
+			}
+		})
+	})
+	if *open != was {
+		slog.Debug("8bit: date input popup", "label", text, "open", *open)
+	}
+	res := DateInputResult{Element: shell, Changed: !date.Equal(old)}
+	if res.Changed {
+		slog.Debug("8bit: date input", "label", text, "date", date.Format("2006-01-02"))
+	}
+	return res
+}