package main

import (
	"github.com/BurntSushi/xgb"
	"github.com/BurntSushi/xgb/render"
	"github.com/BurntSushi/xgb/xproto"
	"log"
	"math/rand"
)

func F64ToFixed(f float64) render.Fixed { return render.Fixed(f * 65536) }
func FixedToF64(f render.Fixed) float64 { return float64(f) / 65536 }

func main() {
	X, err := xgb.NewConn()
	if err != nil {
		log.Fatalln(err)
	}

	if err := render.Init(X); err != nil {
		log.Fatalln(err)
	}

	setup := xproto.Setup(X)
	screen := setup.DefaultScreen(X)

	var visual xproto.Visualid
	var depth byte
	for _, i := range screen.AllowedDepths {
		if i.Depth == 32 {
			// TODO: Could/should check other parameters.
			for _, v := range i.Visuals {
				if v.Class == xproto.VisualClassTrueColor {
					visual = v.VisualId
					depth = i.Depth
					break
				}
			}
		}
	}
	if visual == 0 {
		log.Fatalln("cannot find an RGBA TrueColor visual")
	}

	mid, err := xproto.NewColormapId(X)
	if err != nil {
		log.Fatalln(err)
	}

	_ = xproto.CreateColormap(
		X, xproto.ColormapAllocNone, mid, screen.Root, visual)

	wid, err := xproto.NewWindowId(X)
	if err != nil {
		log.Fatalln(err)
	}

	// Border pixel and colormap are required when depth differs from parent.
	_ = xproto.CreateWindow(X, depth, wid, screen.Root,
		0, 0, 500, 500, 0, xproto.WindowClassInputOutput,
		visual, xproto.CwBorderPixel|xproto.CwColormap,
		[]uint32{0, uint32(mid)})

	// This could be included in CreateWindow parameters.
	_ = xproto.ChangeWindowAttributes(X, wid,
		xproto.CwBackPixel|xproto.CwEventMask, []uint32{0x80808080,
			xproto.EventMaskStructureNotify | xproto.EventMaskKeyPress |
				xproto.EventMaskExposure})

	title := []byte("Gradient")
	_ = xproto.ChangeProperty(X, xproto.PropModeReplace, wid, xproto.AtomWmName,
		xproto.AtomString, 8, uint32(len(title)), title)

	_ = xproto.MapWindow(X, wid)

	pformats, err := render.QueryPictFormats(X).Reply()
	if err != nil {
		log.Fatalln(err)
	}

	// Similar to XRenderFindVisualFormat.
	// The DefaultScreen is almost certain to be zero.
	var pformat render.Pictformat
	for _, pd := range pformats.Screens[X.DefaultScreen].Depths {
		// This check seems to be slightly extraneous.
		if pd.Depth != depth {
			continue
		}
		for _, pv := range pd.Visuals {
			if pv.Visual == visual {
				pformat = pv.Format
			}
		}
	}

	// ...or just scan through pformats.Formats and look for matches, which is
	// what XRenderFindStandardFormat in Xlib does as well as exp/shiny.

	pid, err := render.NewPictureId(X)
	if err != nil {
		log.Fatalln(err)
	}
	render.CreatePicture(X, pid, xproto.Drawable(wid), pformat, 0, []uint32{})

	// Reserve an ID for the gradient.
	gid, err := render.NewPictureId(X)
	if err != nil {
		log.Fatalln(err)
	}

	var from, to render.Color
	recolor := func() {
		start := rand.Uint32() & 0xffffff
		from = render.Color{
			Red:   0x101 * uint16((start>>16)&0xff),
			Green: 0x101 * uint16((start>>8)&0xff),
			Blue:  0x101 * uint16(start&0xff),
			Alpha: 0xffff,
		}

		end := rand.Uint32() & 0xffffff
		to = render.Color{
			Red:   0x101 * uint16((end>>16)&0xff),
			Green: 0x101 * uint16((end>>8)&0xff),
			Blue:  0x101 * uint16(end&0xff),
			Alpha: 0xffff,
		}
	}

	var w, h uint16
	gradient := func() {
		if w < 100 || h < 100 {
			return
		}

		_ = render.CreateLinearGradient(X, gid,
			render.Pointfix{F64ToFixed(0), F64ToFixed(0)},
			render.Pointfix{F64ToFixed(0), F64ToFixed(float64(h) - 100)},
			2, []render.Fixed{F64ToFixed(0), F64ToFixed(1)},
			[]render.Color{from, to})

		_ = render.Composite(X, render.PictOpSrc, gid, render.PictureNone, pid,
			0, 0, 0, 0, 50, 50, w-100, h-100)

		_ = render.FreePicture(X, gid)
	}

	for {
		ev, xerr := X.WaitForEvent()
		if xerr != nil {
			log.Printf("Error: %s\n", xerr)
			return
		}
		if ev == nil {
			return
		}

		log.Printf("Event: %s\n", ev)
		switch e := ev.(type) {
		case xproto.UnmapNotifyEvent:
			return

		case xproto.ConfigureNotifyEvent:
			w, h = e.Width, e.Height
			recolor()

		case xproto.KeyPressEvent:
			recolor()
			gradient()

		case xproto.ExposeEvent:
			gradient()
		}
	}

}