package main

import (
	"fmt"
	"runtime"

	"golang.org/x/mobile/app"
	"golang.org/x/mobile/event/lifecycle"
	"golang.org/x/mobile/event/paint"
	"golang.org/x/mobile/event/size"
	"golang.org/x/mobile/event/touch"
	"golang.org/x/mobile/gl"
)

func main() {
	app.Main(func(a app.App) {
		var glctx gl.Context
		for e := range a.Events() {
			switch e := a.Filter(e).(type) {
			case lifecycle.Event:
				switch e.Crosses(lifecycle.StageVisible) {
				case lifecycle.CrossOn:
					glctx, _ = e.DrawContext.(gl.Context)
					onStart()
				case lifecycle.CrossOff:
					onStop()
					glctx = nil
				}
			case size.Event:
				onResize(e)
			case paint.Event:
				if glctx == nil {
					continue
				}
				onDraw(glctx)
				a.Publish()
			case touch.Event:
				onTouch(e)
			}
		}
	})
}

func onStart() {
	fmt.Println("App started")
}

func onStop() {
	fmt.Println("App stopped")
}

func onResize(e size.Event) {
	runtime.LockOSThread()
	gl.Viewport(0, 0, e.WidthPx, e.HeightPx)
	runtime.UnlockOSThread()
}

func onDraw(glctx gl.Context) {
	glctx.ClearColor(0.1, 0.1, 0.1, 1)
	glctx.Clear(gl.COLOR_BUFFER_BIT)
}

func onTouch(e touch.Event) {
	fmt.Printf("Touch event: X: %f, Y: %f\n", e.X, e.Y)
}