package ui

import (
	"image"
	"time"

	"gioui.org/app"
	"gioui.org/layout"
	"gioui.org/op"
	"gioui.org/op/clip"
	"gioui.org/op/paint"
	"gioui.org/unit"
	"gioui.org/widget/material"
)

// toast is a transient top-of-window notification ("Copied", error
// messages, etc). It is non-modal: drawing it does not consume pointer
// input. Lifetime is governed by `until`; the next frame after the
// deadline simply skips drawing.
type toast struct {
	msg   string
	until time.Time
}

const toastDuration = 1500 * time.Millisecond

// Show stores the message and schedules an Invalidate after the toast
// expires so the window redraws and removes it without waiting for the
// next user interaction.
func (t *toast) Show(msg string, w *app.Window) {
	t.msg = msg
	t.until = time.Now().Add(toastDuration)
	go func(deadline time.Time) {
		time.Sleep(time.Until(deadline) + 50*time.Millisecond)
		w.Invalidate()
	}(t.until)
}

// active reports whether the toast should be drawn this frame.
func (t *toast) active() bool {
	return t.msg != "" && time.Now().Before(t.until)
}

// draw paints the toast as an overlay centered near the top of gtx.
// Call AFTER laying out the rest of the frame so it stacks on top.
func (t *toast) draw(gtx layout.Context, th *material.Theme) {
	if !t.active() {
		return
	}
	bg := activePalette.ToastBg
	fg := activePalette.ToastFg

	macro := op.Record(gtx.Ops)
	pad := layout.UniformInset(unit.Dp(10))
	dims := pad.Layout(gtx, func(gtx layout.Context) layout.Dimensions {
		lbl := material.Body2(th, t.msg)
		lbl.Color = fg
		return lbl.Layout(gtx)
	})
	call := macro.Stop()

	// Center horizontally near the top.
	x := (gtx.Constraints.Max.X - dims.Size.X) / 2
	if x < 0 {
		x = 0
	}
	y := gtx.Dp(unit.Dp(12))

	stack := op.Offset(image.Point{X: x, Y: y}).Push(gtx.Ops)
	rrect := clip.RRect{
		Rect: image.Rectangle{Max: dims.Size},
		SE:   gtx.Dp(unit.Dp(6)),
		SW:   gtx.Dp(unit.Dp(6)),
		NE:   gtx.Dp(unit.Dp(6)),
		NW:   gtx.Dp(unit.Dp(6)),
	}
	bgArea := rrect.Push(gtx.Ops)
	paint.ColorOp{Color: bg}.Add(gtx.Ops)
	paint.PaintOp{}.Add(gtx.Ops)
	bgArea.Pop()
	call.Add(gtx.Ops)
	stack.Pop()
}