// main
package main

import (
	"image"
	_ "image/png"
	"math/rand"
	"os"
	"time"

	"github.com/faiface/pixel"
	"github.com/faiface/pixel/pixelgl"
	"golang.org/x/image/colornames"
)

//open file from the system
func loadPicture(path string) (pixel.Picture, error) {
	file, err := os.Open(path)
	if err != nil {
		return nil, err
	}

	//user 'defer' to close the file later on
	defer file.Close()

	//decode the file to find it's type
	img, _, err := image.Decode(file)
	if err != nil {
		return nil, err
	}
	return pixel.PictureDataFromImage(img), nil
}

//Pixel's main function (because GO forced them to do it this way)
func run() {
	//set the Window parameters
	cfg := pixelgl.WindowConfig{
		Title:  "Pixel Rocks!",
		Bounds: pixel.R(0, 0, 1024, 768),
		VSync:  true,
	}

	//create a window and pass the parameters
	win, err := pixelgl.NewWindow(cfg)
	if err != nil {
		panic(err)
	}

	spritesheet, err := loadPicture("trees.png")
	if err != nil {
		panic(err)
	}

	var treesFrames []pixel.Rect
	for x := spritesheet.Bounds().Min.X; x < spritesheet.Bounds().Max.X; x += 32 {
		for y := spritesheet.Bounds().Min.Y; y < spritesheet.Bounds().Max.Y; y += 32 {
			treesFrames = append(treesFrames, pixel.R(x, y, x+32, y+32))
		}
	}

	//camera
	var (
		camPos   = pixel.ZV
		camSpeed = 500.0
		trees    []*pixel.Sprite
		matrices []pixel.Matrix
	)

	last := time.Now()
	//loop until window is closed by "X" button
	for !win.Closed() {
		dt := time.Since(last).Seconds()
		last = time.Now()

		cam := pixel.IM.Moved(win.Bounds().Center().Sub(camPos))
		win.SetMatrix(cam)

		if win.JustPressed(pixelgl.MouseButtonLeft) {
			tree := pixel.NewSprite(spritesheet, treesFrames[rand.Intn(len(treesFrames))])
			trees = append(trees, tree)
			mouse := cam.Unproject(win.MousePosition())
			matrices = append(matrices, pixel.IM.Scaled(pixel.ZV, 4).Moved(mouse))
		}

		if win.Pressed(pixelgl.KeyA) {
			camPos.X -= camSpeed * dt
		}

		if win.Pressed(pixelgl.KeyD) {
			camPos.X += camSpeed * dt
		}

		if win.Pressed(pixelgl.KeyS) {
			camPos.Y -= camSpeed * dt
		}

		if win.Pressed(pixelgl.KeyW) {
			camPos.Y += camSpeed * dt
		}
		//refresh screen and set background color
		win.Clear(colornames.Forestgreen)
		for i, tree := range trees {
			tree.Draw(win, matrices[i])
		}
		//update the window
		win.Update()
	}
}

func main() {
	pixelgl.Run(run)
}