package ui

import (
	"image"

	"gioui.org/layout"
	"gioui.org/op/clip"
	"gioui.org/text"
	"gioui.org/widget/material"
)

// Renderer consumes a slice of elements and draws them.
type Renderer struct {
	theme Theme
	shp   *text.Shaper
}

// New creates a new Renderer.
func New(th Theme, shp *text.Shaper) *Renderer {
	return &Renderer{theme: th, shp: shp}
}

// Draw iterates elements and draws each in slice order (back-to-front).
func (r *Renderer) Draw(gtx layout.Context, elems []Element) {
	for _, e := range elems {
		if !e.Visible() {
			continue
		}
		switch v := e.(type) {
		case Label:
			r.drawLabel(gtx, v)
		case ListView:
			r.drawListView(gtx, v)
		default:
			// unknown element type, skip
		}
	}
}

func (r *Renderer) drawLabel(gtx layout.Context, l Label) {
	reg := l.Region()
	c := clip.Rect{
		Min: image.Point{X: int(reg.X), Y: int(reg.Y)},
		Max: image.Point{X: int(reg.X + reg.W), Y: int(reg.Y + reg.H)},
	}.Push(gtx.Ops)

	th := material.NewTheme()
	th.Shaper = r.shp
	size := l.FontSize
	if size == 0 {
		size = r.theme.FontSize
	}
	material.Label(th, size, l.Text).Layout(gtx)
	c.Pop()
}

func (r *Renderer) drawListView(gtx layout.Context, lv ListView) {
	reg := lv.Region()
	c := clip.Rect{
		Min: image.Point{X: int(reg.X), Y: int(reg.Y)},
		Max: image.Point{X: int(reg.X + reg.W), Y: int(reg.Y + reg.H)},
	}.Push(gtx.Ops)

	th := material.NewTheme()
	th.Shaper = r.shp
	for _, item := range lv.Items {
		material.Label(th, r.theme.FontSize, item.Text).Layout(gtx)
	}
	c.Pop()
}