package main

import (
	"github.com/BurntSushi/xgb"
	//"github.com/BurntSushi/xgb/xkb"
	"github.com/BurntSushi/xgb/xproto"
	"log"
)

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

	/*
		// Use the extension if available, makes better use of state bits.
		if err := xkb.Init(X); err == nil {
			if _, err := xkb.UseExtension(X, 1, 0).Reply(); err != nil {
				log.Fatalln(err)
			}
		}
	*/

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

	visual, depth := screen.RootVisual, screen.RootDepth
	// TODO: We should check that we find it, though we don't /need/ alpha here,
	// it's just a minor improvement--affects the backpixel value.
	for _, i := range screen.AllowedDepths {
		for _, v := range i.Visuals {
			// TODO: Could/should check other parameters.
			if i.Depth == 32 && v.Class == xproto.VisualClassTrueColor {
				visual, depth = v.VisualId, i.Depth
				break
			}
		}
	}

	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.CwBackPixel|xproto.CwBorderPixel|xproto.CwEventMask|
			xproto.CwColormap, []uint32{0x80808080, 0,
			xproto.EventMaskStructureNotify | xproto.EventMaskKeyPress |
				/* KeymapNotify */ xproto.EventMaskKeymapState, uint32(mid)})

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

	_ = xproto.MapWindow(X, wid)

	mapping, err := xproto.GetKeyboardMapping(X, setup.MinKeycode,
		byte(setup.MaxKeycode-setup.MinKeycode+1)).Reply()
	if err != nil {
		log.Fatalln(err)
	}

	// The order is "Shift, Lock, Control, Mod1, Mod2, Mod3, Mod4, and Mod5."
	mm, err := xproto.GetModifierMapping(X).Reply()
	if err != nil {
		log.Fatalln(err)
	}

	// XXX: This seems pointless, the key will just end up switching groups
	// instead of levels without full XKB handling. Though perhaps it might
	// at least work as intended when there's only one XKB group.
	const MODE_SWITCH = 0xff7e

	var modeSwitchMask uint16
	for mod := 0; mod < 8; mod++ {
		perMod := int(mm.KeycodesPerModifier)
		for _, kc := range mm.Keycodes[mod*perMod : (mod+1)*perMod] {
			if kc == 0 {
				continue
			}

			perKc := int(mapping.KeysymsPerKeycode)
			k := int(kc - setup.MinKeycode)
			for _, ks := range mapping.Keysyms[k*perKc : (k+1)*perKc] {
				if ks == MODE_SWITCH {
					modeSwitchMask |= 1 << uint(mod)
				}
			}
		}
	}

	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.KeymapNotifyEvent:
			// e.Keys is a 32 * 8 large bitmap indicating which keys are
			// currently pressed down. This is sent "after every EnterNotify
			// and FocusIn" but it also seems to fire when the keyboard layout
			// changes. aixterm manual even speaks of that explicitly.
			//
			// But since changing the effective group involves no changes to
			// the compatibility mapping, there's nothing for us to do.

		case xproto.MappingNotifyEvent:
			// e.FirstKeyCode .. e.Count changes have happened but rereading
			// everything is the simpler thing to do.
			mapping, err = xproto.GetKeyboardMapping(X, setup.MinKeycode,
				byte(setup.MaxKeycode-setup.MinKeycode+1)).Reply()
			if err != nil {
				log.Fatalln(err)
			}

			// TODO: We should also repeat the search for MODE SWITCH.

		case xproto.KeyPressEvent:
			step := int(mapping.KeysymsPerKeycode)
			from := int(e.Detail-setup.MinKeycode) * step
			ks := mapping.Keysyms[from : from+step]

			// Strip trailing NoSymbol entries.
			for len(ks) > 0 && ks[len(ks)-1] == 0 {
				ks = ks[:len(ks)-1]
			}

			// Expand back to at least 4.
			switch {
			case len(ks) == 1:
				ks = append(ks, 0, ks[0], 0)
			case len(ks) == 2:
				ks = append(ks, ks[0], ks[1])
			case len(ks) == 3:
				ks = append(ks, 0)
			}

			// Other silly expansion rules, only applied to basic ASCII.
			if ks[1] == 0 {
				ks[1] = ks[0]
				if ks[0] >= 'A' && ks[0] <= 'Z' ||
					ks[0] >= 'a' && ks[0] <= 'z' {
					ks[0] = ks[0] | 32
					ks[1] = ks[0] &^ 32
				}
			}

			if ks[3] == 0 {
				ks[3] = ks[2]
				if ks[2] >= 'A' && ks[2] <= 'Z' ||
					ks[2] >= 'a' && ks[2] <= 'z' {
					ks[2] = ks[2] | 32
					ks[3] = ks[2] &^ 32
				}
			}

			// We only have enough information to switch between two groups.
			offset := 0
			if e.State&modeSwitchMask != 0 {
				offset += 2
			}

			var result xproto.Keysym

			shift := e.State&xproto.ModMaskShift != 0
			lock := e.State&xproto.ModMaskLock != 0
			switch {
			case !shift && !lock:
				result = ks[offset+0]
			case !shift && lock:
				if ks[offset+0] >= 'a' && ks[offset+0] <= 'z' {
					result = ks[offset+1]
				} else {
					result = ks[offset+0]
				}
			case shift && lock:
				if ks[offset+1] >= 'a' && ks[offset+1] <= 'z' {
					result = ks[offset+1] &^ 32
				} else {
					result = ks[offset+1]
				}
			case shift:
				result = ks[offset+1]
			}

			if result <= 0xff {
				log.Printf("%c (Latin-1)\n", rune(result))
			} else {
				log.Println(result)
			}
		}
	}
}