package main

import (
	"flag"
	"image"
	"log"
	"math"
	"os"
	"sort"

	"github.com/hajimehoshi/ebiten"

	"code.ur.gs/lupine/ordoor/internal/assetstore"
	"code.ur.gs/lupine/ordoor/internal/ui"
)

var (
	gamePath = flag.String("game-path", "./orig", "Path to a WH40K: Chaos Gate installation")
	gameMap  = flag.String("map", "", "Name of a map, e.g., Chapter01")
)

type env struct {
	assets *assetstore.AssetStore
	area   *assetstore.Map

	step      int
	state     state
	lastState state
}

type state struct {
	zoom   float64
	origin image.Point
	zIdx   int
}

func main() {
	flag.Parse()

	if *gamePath == "" || *gameMap == "" {
		flag.Usage()
		os.Exit(1)
	}

	assets, err := assetstore.New(*gamePath)
	if err != nil {
		log.Fatalf("Failed to scan root directory %v: %v", *gamePath, err)
	}

	area, err := assets.Map(*gameMap)
	if err != nil {
		log.Fatalf("Failed to load map %v: %v", *gameMap, err)
	}

	state := state{
		zoom:   1.0,
		origin: image.Point{0, 3000}, // FIXME: haxxx
		zIdx:   1,
	}
	env := &env{
		area:      area,
		assets:    assets,
		state:     state,
		lastState: state,
	}

	win, err := ui.NewWindow("View Map " + *gameMap)
	if err != nil {
		log.Fatal("Couldn't create window: %v", err)
	}

	// TODO: click to view cell data

	win.OnKeyUp(ebiten.KeyLeft, env.changeOrigin(-64, +0))
	win.OnKeyUp(ebiten.KeyRight, env.changeOrigin(+64, +0))
	win.OnKeyUp(ebiten.KeyUp, env.changeOrigin(+0, -64))
	win.OnKeyUp(ebiten.KeyDown, env.changeOrigin(+0, +64))
	win.OnMouseWheel(env.changeZoom)

	for i := 0; i < 6; i++ {
		win.OnKeyUp(ebiten.Key1+ebiten.Key(i), env.setZIdx(i+1))
	}

	if err := win.Run(env.Update, env.Draw); err != nil {
		log.Fatal(err)
	}
}

func (e *env) Update() error {
	if e.step == 0 || e.lastState != e.state {
		log.Printf("zoom=%.2f zIdx=%v camPos=%#v", e.state.zoom, e.state.zIdx, e.state.origin)
	}

	e.lastState = e.state
	e.step += 1

	return nil
}

func (e *env) Draw(screen *ebiten.Image) error {
	// Bounds clipping
	// http://www.java-gaming.org/index.php?topic=24922.0
	// https://stackoverflow.com/questions/892811/drawing-isometric-game-worlds
	// https://gamedev.stackexchange.com/questions/25896/how-do-i-find-which-isometric-tiles-are-inside-the-cameras-current-view

	sw, sh := screen.Size()

	topLeft := pixToCell(e.state.origin)
	topLeft.X -= 1 // Otherwise we miss half a cell on alternate rows on the left

	bottomRight := pixToCell(image.Pt(e.state.origin.X+sw, e.state.origin.Y+sh))

	// X+Y is constant for all tiles in a column
	// X-Y is constant for all tiles in a row
	// However, the drawing order is odd unless we reorder explicitly.
	toDraw := []image.Point{}
	for a := topLeft.X + topLeft.Y; a <= bottomRight.X+bottomRight.Y; a++ {
		for b := topLeft.X - topLeft.Y; b <= bottomRight.X-bottomRight.Y; b++ {
			if b&1 != a&1 {
				continue
			}

			pt := image.Pt((a+b)/2, (a-b)/2)

			if !pt.In(e.area.Rect) {
				continue
			}
			toDraw = append(toDraw, pt)
		}
	}

	sort.Slice(toDraw, func(i, j int) bool {
		iPix := cellToPix(toDraw[i])
		jPix := cellToPix(toDraw[j])

		if iPix.Y < jPix.Y {
			return true
		}

		if iPix.Y == jPix.Y {
			return iPix.X < jPix.X
		}

		return false
	})

	for _, pt := range toDraw {
		for z := 0; z <= e.state.zIdx; z++ {
			if err := e.renderCell(pt.X, pt.Y, z, screen); err != nil {
				return err
			}
		}
	}

	return nil
}

func (e *env) renderCell(x, y, z int, screen *ebiten.Image) error {
	sprites, err := e.area.SpritesForCell(x, y, z)
	if err != nil {
		return err
	}

	iso := ebiten.GeoM{}
	iso.Translate(-float64(e.state.origin.X), -float64(e.state.origin.Y))

	pix := cellToPix(image.Pt(x, y))
	iso.Translate(float64(pix.X), float64(pix.Y))

	if e.step%30 == 0 {
		//	log.Printf("x=%v y=%v z=%v", pix.X-e.state.origin.X, pix.Y-e.state.origin.Y, z)
	}

	// Taking the Z index away *seems* to draw the object in the correct place.
	// FIXME: There are some artifacts, investigate more
	iso.Translate(0.0, -float64(z*48.0)) // offset for Z index

	// TODO: iso.Scale(e.state.zoom, e.state.zoom) // apply current zoom factor

	for _, spr := range sprites {
		iso.Translate(float64(spr.XOffset), float64(spr.YOffset))
		if err := screen.DrawImage(spr.Image, &ebiten.DrawImageOptions{GeoM: iso}); err != nil {
			return err
		}
		iso.Translate(float64(-spr.XOffset), float64(-spr.YOffset))
	}

	return nil
}

func (e *env) changeOrigin(byX, byY int) func() {
	return func() {
		e.state.origin.X += byX
		e.state.origin.Y += byY
	}
}

func (e *env) changeZoom(_, y float64) {
	// Zoom in and out with the mouse wheel
	e.state.zoom *= math.Pow(1.2, y)
}

func (e *env) setZIdx(to int) func() {
	return func() {
		e.state.zIdx = to
	}
}

const (
	cellWidth  = 64
	cellHeight = 64
)

// Doesn't take the camera or Z level into account
func cellToPix(pt image.Point) image.Point {
	return image.Pt(
		(pt.X-pt.Y)*cellWidth,
		(pt.X+pt.Y)*cellHeight/2,
	)
}

// Doesn't take the camera or Z level into account
func pixToCell(pt image.Point) image.Point {
	return image.Pt(
		pt.Y/cellHeight+pt.X/(cellWidth*2),
		pt.Y/cellHeight-pt.X/(cellWidth*2),
	)
}