// main
package main

import (
	"image"
	_ "image/png"
	"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)
	}

	//smooth the edges of the image (antialiasing)
	win.SetSmooth(true)

	//load a specific image and catch any errors
	pic, err := loadPicture("hiking.png")
	if err != nil {
		panic(err)
	}

	//create a sprite using the loaded image
	sprite := pixel.NewSprite(pic, pic.Bounds())

	//set the angle of the image
	angle := 0.0

	//set the time to compare later
	last := time.Now()

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

		//set the angle according to delta time
		angle += 3 * dt

		//refresh screen and set background color
		win.Clear(colornames.Firebrick)

		//set the matrix and location of spirte in window
		mat := pixel.IM
		mat = mat.Rotated(pixel.ZV, angle)
		mat = mat.Moved(win.Bounds().Center())
		sprite.Draw(win, mat)

		//update the window
		win.Update()
	}
}

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