package main

import (
	"context"
	"fmt"
	"log"
	"math"
	"os"
	"os/signal"
	"syscall"

	"github.com/linuxdeepin/go-x11-client/util/cursor"
	"github.com/linuxdeepin/go-x11-client/util/mousebind"

	x "github.com/linuxdeepin/go-x11-client"
)

// Give names to the events we care about
const (
	Pressed  uint8 = 4
	Released       = 5
)

type dragger struct {
	events chan x.GenericEvent
	start  [2]int16
	end    [2]int16
}

// Watch begins the process of dragger watching for drag events
func (s *dragger) Watch(ctx context.Context) int {
	c := make(chan int, 1)
	for {
		select {
		case c <- s.watch():
			return <-c
		case _ = <-ctx.Done():
			return 0
		}
	}
}

func (s *dragger) watch() int {
	for {
		generic := <-s.events
		event, err := x.NewButtonPressEvent(generic)
		if err != nil {
			log.Fatal(err)
		}

		if generic.GetEventCode() == Pressed {
			s.start = [2]int16{event.EventX, event.EventY}
		} else {
			s.end = [2]int16{event.EventX, event.EventY}
			return s.distance()
		}
	}
}

func (s dragger) distance() int {
	diffx := int(s.start[0] - s.end[0])
	diffy := int(s.start[1] - s.end[1])
	distance := math.Sqrt(float64((diffx * diffx) + (diffy * diffy)))
	return int(distance)
}

func loadCursor(conn *x.Conn) (x.Cursor, error) {
	img, err := cursor.LoadImage("default", "crosshair", 2)
	if err != nil {
		return x.CursorNone, err
	}

	return img.LoadCursor(conn, "")
}

func main() {
	stop := make(chan os.Signal)
	signal.Notify(stop, os.Interrupt, syscall.SIGTERM, syscall.SIGINT)

	display, err := x.NewConnDisplay("")
	if err != nil {
		log.Fatal(err)
	}
	defer display.Close()

	screen := display.GetDefaultScreen()

	curs, err := loadCursor(display)
	if err != nil {
		log.Fatal(err)
	}

	mask := uint16(x.EventMaskButtonPress | x.EventMaskButtonRelease)
	err = mousebind.GrabPointer(display, screen.Root, mask, x.None, curs)
	if err != nil {
		log.Fatal(err)
	}

	defer mousebind.UngrabPointer(display)

	eventChan := display.MakeAndAddEventChan(1)
	responseChan := make(chan int, 1)

	ctx, cancel := context.WithCancel(context.Background())
	d := dragger{events: eventChan}

	for {
		select {
		case responseChan <- d.Watch(ctx):
			fmt.Println(<-responseChan)
			os.Exit(0)
		case <-stop:
			cancel()
			os.Exit(0)
		}
	}
}