package main

import (
	"fmt"
	"image/color"
	"log"
	"math/rand"
	"time"

	"golang.org/x/image/font"
	"golang.org/x/image/font/opentype"

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
	"github.com/hajimehoshi/ebiten/v2/examples/resources/fonts"
	"github.com/hajimehoshi/ebiten/v2/inpututil"
	"github.com/hajimehoshi/ebiten/v2/text"
)

var (
	mplusNormalFont font.Face
)

func init() {
	// TODO: don't use the ebiten example code font
	tt, err := opentype.Parse(fonts.MPlus1pRegular_ttf)
	if err != nil {
		log.Fatal(err)
	}

	const dpi = 72
	mplusNormalFont, err = opentype.NewFace(tt, &opentype.FaceOptions{
		Size:    24,
		DPI:     dpi,
		Hinting: font.HintingFull,
	})
	if err != nil {
		log.Fatal(err)
	}
	rand.Seed(time.Now().UnixMicro())
}

type Kind uint8

const (
	Empty Kind = iota
	Worm
	Food
)

func (k Kind) String() string {
	switch k {
	case Empty:
		return "Empty"
	case Worm:
		return "Worm"
	case Food:
		return "Food"
	default:
		return "<unknown>"
	}
}

type Direction uint8

const (
	None Direction = iota
	North
	South
	East
	West
)

func (d Direction) String() string {
	switch d {
	case None:
		return "None"
	case North:
		return "North"
	case South:
		return "South"
	case East:
		return "East"
	case West:
		return "West"
	default:
		return "<unknown>"
	}
}

type Tile struct {
	kind Kind
	dir  Direction
}

func (t Tile) String() string {
	return fmt.Sprintf("%s -- %s", t.kind, t.dir)
}

var EmptyTile = Tile{kind: Empty, dir: None}
var FoodTile = Tile{kind: Food, dir: None}

type point struct {
	x, y int
}

type WormGame struct {
	screenWidth, screenHeight int
	width, height             int

	initLength int
	score      int
	won, lost  bool

	board [][]Tile

	head point
	tail point

	lastMove time.Time
	speed    time.Duration
}

func NewGame(screenWidth, screenHeight int, initLength int, speed time.Duration) *WormGame {
	w := &WormGame{
		screenWidth:  screenWidth,
		screenHeight: screenHeight,
		width:        screenWidth / 4,
		height:       screenHeight / 4,
		initLength:   initLength,
		speed:        speed,
	}
	w.Reset()
	return w
}

func (w *WormGame) Reset() {
	w.lost = false
	w.won = false
	w.score = 0
	w.board = make([][]Tile, w.width)
	for idx := range w.board {
		w.board[idx] = make([]Tile, w.height)
	}

	w.head = point{
		x: w.width / 2,
		y: w.height / 2,
	}

	w.Set(w.head, Worm, East)
	for idx := 1; idx < w.initLength; idx++ {
		w.board[w.head.x-idx][w.head.y] = Tile{kind: Worm, dir: East}
	}
	w.tail = point{w.head.x - w.initLength + 1, w.head.y}
	w.RandomizeFood()
	w.lastMove = time.Now()
}

func (w *WormGame) randomFreeSpace() *point {
	checked := map[point]struct{}{}
	for len(checked) <= w.width*w.height {
		x := rand.Intn(w.width)
		y := rand.Intn(w.height)
		p := point{x, y}
		if _, ok := checked[p]; ok {
			continue
		}
		checked[p] = struct{}{}
		if w.board[x][y].kind == Empty {
			return &p
		}
	}

	return nil
}

func (w *WormGame) RandomizeFood() {
	p := w.randomFreeSpace()
	if p == nil {
		w.won = true
		return
	}
	w.board[p.x][p.y] = FoodTile
}

func (w *WormGame) InBounds(p point) bool {
	return p.x < w.width && p.x >= 0 && p.y < w.height && p.y >= 0
}

func (w *WormGame) MustInBounds(p point) {
	if !w.InBounds(p) {
		panic("out of bounds!")
	}
}

func (w *WormGame) Get(p point) Tile {
	w.MustInBounds(p)
	return w.board[p.x][p.y]
}

func (w *WormGame) Set(p point, kind Kind, dir Direction) {
	w.MustInBounds(p)
	w.board[p.x][p.y] = Tile{kind: kind, dir: dir}
}
func (w *WormGame) SetEmpty(p point) {
	w.MustInBounds(p)
	w.board[p.x][p.y] = EmptyTile
}

func (w *WormGame) AdvanceWorm() {
	dir := w.Get(w.head).dir
	prev := w.head

	switch dir {
	case North:
		if w.head.y-1 > w.height {
			panic("out of bounds")
		}
		w.head.y -= 1
	case South:
		if w.head.y+1 < 0 {
			panic("out of bounds")
		}
		w.head.y += 1
	case East:
		if w.head.x+1 > w.width {
			panic("out of bounds")
		}
		w.head.x += 1
	case West:
		if w.head.x-1 < 0 {
			panic("out of bounds")
		}
		w.head.x -= 1
	}

	// change direction of prev worm segment
	w.Set(prev, Worm, dir)
	// add new worm segment
	w.Set(w.head, Worm, dir)

	tailDir := w.Get(w.tail).dir
	// shorten tail
	w.SetEmpty(w.tail)

	// update tail pointer
	switch tailDir {
	case North:
		w.tail = point{w.tail.x, w.tail.y - 1}
	case South:
		w.tail = point{w.tail.x, w.tail.y + 1}
	case East:
		w.tail = point{w.tail.x + 1, w.tail.y}
	case West:
		w.tail = point{w.tail.x - 1, w.tail.y}
	}

	// update laste move ts
	w.lastMove = time.Now()
}

func (w *WormGame) EmbiggenWorm() {
	tailDir := w.Get(w.tail).dir

	// update tail pointer
	switch tailDir {
	case North:
		w.tail = point{w.tail.x, w.tail.y + 1}
	case South:
		w.tail = point{w.tail.x, w.tail.y - 1}
	case East:
		w.tail = point{w.tail.x - 1, w.tail.y}
	case West:
		w.tail = point{w.tail.x + 1, w.tail.y}
	}

	w.Set(w.tail, Worm, tailDir)
}

func (w *WormGame) Update() error {
	if w.won || w.lost {
		if inpututil.IsKeyJustPressed(ebiten.KeySpace) {
			w.Reset()
		}
		return nil
	}
	up := inpututil.IsKeyJustPressed(ebiten.KeyArrowUp)
	down := inpututil.IsKeyJustPressed(ebiten.KeyArrowDown)
	left := inpututil.IsKeyJustPressed(ebiten.KeyArrowLeft)
	right := inpututil.IsKeyJustPressed(ebiten.KeyArrowRight)

	// cancel out simultaneous up and down
	if up && down {
		up = false
		down = false
	}
	// cancel up simultaneous left and right,
	// also up/down take priority over left/right
	if (left && right) || (up || down) {
		left = false
		right = false
	}

	changedDirection := true
	headTile := w.Get(w.head)

	if up && headTile.dir != South {
		headTile.dir = North
	} else if down && headTile.dir != North {
		headTile.dir = South
	} else if left && headTile.dir != East {
		headTile.dir = West
	} else if right && headTile.dir != West {
		headTile.dir = East
	} else {
		changedDirection = false
	}
	w.Set(w.head, headTile.kind, headTile.dir)

	var next point
	switch headTile.dir {
	case North:
		next = point{w.head.x, w.head.y - 1}
	case South:
		next = point{w.head.x, w.head.y + 1}
	case East:
		next = point{w.head.x + 1, w.head.y}
	case West:
		next = point{w.head.x - 1, w.head.y}
	}

	// don't evaluate space or advance if we didn't change direction and haven't reached timeout
	if !changedDirection && time.Now().Sub(w.lastMove) < w.speed {
		return nil
	}

	var ate bool
	if next.x >= w.width || next.y >= w.height || next.x < 0 || next.y < 0 {
		w.lost = true
	} else {
		tile := w.board[next.x][next.y]
		ate = (tile.kind == Food)
		w.lost = (tile.kind == Worm)
	}

	if w.lost {
		return nil
	}

	if ate {
		w.score += 1
		w.EmbiggenWorm()
		w.RandomizeFood()
	}

	// check if we won (all spaces are worm) and skip moving (since it would be
	// an auto-loss) this is probably close to impossible?
	if w.won {
		return nil
	}

	w.AdvanceWorm()
	return nil
}

func (w *WormGame) Draw(screen *ebiten.Image) {
	screen.Clear()
	for col := range w.board {
		for row := range w.board[col] {
			x := float64(col * 4)
			y := float64(row * 4)
			switch w.board[col][row].kind {
			case Empty:
				ebitenutil.DrawRect(screen, x, y, 4, 4, color.Black)
			case Worm:
				ebitenutil.DrawRect(screen, x, y, 4, 4, color.White)
			case Food:
				ebitenutil.DrawRect(screen, x, y, 4, 4, color.White)
			}
		}
	}

	if w.won {
		text.Draw(screen, fmt.Sprintf("You Win! Score: %d", w.score), mplusNormalFont, 20, w.screenHeight/2, color.White)
		return
	} else if w.lost {
		text.Draw(screen, fmt.Sprintf("Game Over. Score: %d", w.score), mplusNormalFont, 20, w.screenHeight/2, color.White)
		return
	}
}

func (w *WormGame) Layout(outsideWidth, outsideHeight int) (int, int) {
	return w.screenWidth, w.screenHeight
}

const (
	screenWidth  = 320
	screenHeight = 240
)

func main() {
	game := NewGame(screenWidth, screenHeight, 4, 75*time.Millisecond)
	ebiten.SetWindowSize(screenWidth*2, screenHeight*2)
	ebiten.SetWindowTitle("Worm")
	if err := ebiten.RunGame(game); err != nil {
		log.Fatal(err)
	}
}