// Follow X11 selection contents as they are being changed.
package main

import (
	"janouch.name/haven/nexgb"
	"janouch.name/haven/nexgb/xfixes"
	"janouch.name/haven/nexgb/xproto"
	"log"
)

func main() {
	X, err := nexgb.NewConn()
	if err != nil {
		log.Fatalln(err)
	}
	if err := xfixes.Init(X); err != nil {
		log.Fatalln(err)
	}

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

	// Resolve a few required atoms that are not static in the core protocol.
	const (
		clipboard  = "CLIPBOARD"
		utf8String = "UTF8_STRING"
		incr       = "INCR"
	)

	atomCLIPBOARD, err := xproto.InternAtom(X, false,
		uint16(len(clipboard)), clipboard).Reply()
	if err != nil {
		log.Fatalln(err)
	}

	atomUTF8String, err := xproto.InternAtom(X, false,
		uint16(len(utf8String)), utf8String).Reply()
	if err != nil {
		log.Fatalln(err)
	}

	atomINCR, err := xproto.InternAtom(X, false,
		uint16(len(incr)), incr).Reply()
	if err != nil {
		log.Fatalln(err)
	}

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

	_ = xproto.CreateWindow(X, screen.RootDepth, wid, screen.Root, 0, 0, 1, 1,
		0, xproto.WindowClassInputOutput, screen.RootVisual, xproto.CwEventMask,
		[]uint32{xproto.EventMaskPropertyChange})

	// Select for update events of each selection.
	_ = xfixes.QueryVersion(X, xfixes.MajorVersion, xfixes.MinorVersion)

	_ = xfixes.SelectSelectionInput(X, wid,
		xproto.AtomPrimary, xfixes.SelectionEventMaskSetSelectionOwner|
			xfixes.SelectionEventMaskSelectionWindowDestroy|
			xfixes.SelectionEventMaskSelectionClientClose)

	_ = xfixes.SelectSelectionInput(X, wid,
		atomCLIPBOARD.Atom, xfixes.SelectionEventMaskSetSelectionOwner|
			xfixes.SelectionEventMaskSelectionWindowDestroy|
			xfixes.SelectionEventMaskSelectionClientClose)

	type selectionState struct {
		name       string           // name of the selection
		inProgress xproto.Timestamp // timestamp of retrieved selection
		buffer     []byte           // UTF-8 text buffer
		incr       bool             // INCR running
		incrFailed bool             // INCR failure indicator
	}
	states := map[xproto.Atom]*selectionState{
		xproto.AtomPrimary: {name: "PRIMARY"},
		atomCLIPBOARD.Atom: {name: "CLIPBOARD"},
	}

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

		switch e := ev.(type) {
		case xfixes.SelectionNotifyEvent:
			state, ok := states[e.Selection]
			if !ok {
				break
			}

			// Not checking whether we should give up when our current retrieval
			// attempt is interrupted--the timeout mostly solves this.
			if e.Owner == xproto.WindowNone {
				// This may potentially log before a request for past data
				// finishes, if only because of INCR. Just saying.
				log.Printf("%s: -\n", state.name)
				break
			}

			// Don't try to process two things at once.  Each request gets a few
			// seconds to finish, then we move on, hoping that a property race
			// doesn't commence.  Ideally we'd set up a separate queue for these
			// skipped requests and process them later.
			if state.inProgress != 0 && e.Timestamp-state.inProgress < 5000 {
				break
			}

			// ICCCM says we should ensure the named property doesn't exist.
			_ = xproto.DeleteProperty(X, e.Window, e.Selection)

			_ = xproto.ConvertSelection(X, e.Window, e.Selection,
				atomUTF8String.Atom, e.Selection, e.Timestamp)

			state.inProgress = e.Timestamp
			state.incr = false

		case xproto.SelectionNotifyEvent:
			state, ok := states[e.Selection]
			if e.Requestor != wid || !ok || e.Time != state.inProgress {
				break
			}

			state.inProgress = 0
			if e.Property == xproto.AtomNone {
				break
			}

			// XXX: This is simplified and doesn't necessarily read it all.
			// Maybe we could use setup.MaximumRequestLength.
			// Though xorg-xserver doesn't seem to limit the length of replies
			// or even the length of properties in the first place.
			// It only has a huge (0xffffffff - sizeof(xChangePropertyReq))/4
			// limit for ChangeProperty requests, which is way more than
			// max-request-len (normally 0xffff), even though I can't
			// XChangeProperty more than 0xffffe0 bytes at a time.
			reply, err := xproto.GetProperty(X, false, /* delete */
				e.Requestor, e.Property, xproto.GetPropertyTypeAny,
				0, 0x8000).Reply()
			if err != nil {
				break
			}

			state.buffer = nil

			// When you select a lot of text in VIM, it starts the ICCCM
			// INCR mechanism, from which there is no opt-out.
			if reply.Type == atomINCR.Atom {
				state.inProgress = e.Time
				state.incr = true
				state.incrFailed = false
			} else if reply.Type == atomUTF8String.Atom && reply.Format == 8 {
				log.Printf("%s: '%s'\n", state.name, string(reply.Value))
			}

			_ = xproto.DeleteProperty(X, e.Requestor, e.Property)

		case xproto.PropertyNotifyEvent:
			state, ok := states[e.Atom]
			if e.Window != wid || e.State != xproto.PropertyNewValue ||
				!ok || !state.incr {
				break
			}

			reply, err := xproto.GetProperty(X, false, /* delete */
				e.Window, e.Atom, xproto.GetPropertyTypeAny, 0, 0x8000).Reply()
			if err != nil {
				state.incrFailed = true
				break
			}

			if reply.Type == atomUTF8String.Atom && reply.Format == 8 {
				state.buffer = append(state.buffer, reply.Value...)
			} else {
				// We need to keep deleting the property.
				state.incrFailed = true
			}

			if reply.ValueLen == 0 {
				if !state.incrFailed {
					log.Printf("%s: '%s'\n",
						state.name, string(state.buffer))
				}
				state.inProgress = 0
				state.incr = false
			}

			_ = xproto.DeleteProperty(X, e.Window, e.Atom)
		}
	}
}