// +build example jsgo

package main

import (
        "bytes"
        "fmt"
        "image"
        _ "image/png"
        "log"
        "math"
        "math/rand"

        "github.com/hajimehoshi/ebiten"
        "github.com/hajimehoshi/ebiten/ebitenutil"
        "github.com/hajimehoshi/ebiten/examples/resources/images"
)

const (
        screenWidth  = 320
        screenHeight = 240
        maxAngle     = 256
)

var (
        ebitenImage *ebiten.Image
)

type Sprite struct {
        imageWidth  int
        imageHeight int
        x           int
        y           int
        vx          int
        vy          int
        angle       int
}

func (s *Sprite) Update() {
        s.x += s.vx
        s.y += s.vy
        if s.x < 0 {
                s.x = -s.x
                s.vx = -s.vx
        } else if screenWidth <= s.x+s.imageWidth {
                s.x = 2*(screenWidth-s.imageWidth) - s.x
                s.vx = -s.vx
        }
        if s.y < 0 {
                s.y = -s.y
                s.vy = -s.vy
        } else if screenHeight <= s.y+s.imageHeight {
                s.y = 2*(screenHeight-s.imageHeight) - s.y
                s.vy = -s.vy
        }
        s.angle++
        s.angle %= maxAngle
}

type Sprites struct {
        sprites []*Sprite
        num     int
}

func (s *Sprites) Update() {
        for _, sprite := range s.sprites {
                sprite.Update()
        }
}

const (
        MinSprites = 0
        MaxSprites = 50000
)

var (
        sprites = &Sprites{make([]*Sprite, MaxSprites), 500}
        op      = &ebiten.DrawImageOptions{}
)

func init() {
        // Decode image from a byte slice instead of a file so that
        // this example works in any working directory.
        // If you want to use a file, there are some options:
        // 1) Use os.Open and pass the file to the image decoder.
        //    This is a very regular way, but doesn't work on browsers.
        // 2) Use ebitenutil.OpenFile and pass the file to the image decoder.
        //    This works even on browsers.
        // 3) Use ebitenutil.NewImageFromFile to create an ebiten.Image directly from a file.
        //    This also works on browsers.
        img, _, err := image.Decode(bytes.NewReader(images.Ebiten_png))
        if err != nil {
                log.Fatal(err)
        }
        origEbitenImage, _ := ebiten.NewImageFromImage(img, ebiten.FilterDefault)

        w, h := origEbitenImage.Size()
        ebitenImage, _ = ebiten.NewImage(w, h, ebiten.FilterNearest)

        op := &ebiten.DrawImageOptions{}
        op.ColorM.Scale(1, 1, 1, 0.5)
        ebitenImage.DrawImage(origEbitenImage, op)

        for i := range sprites.sprites {
                w, h := ebitenImage.Size()
                x, y := rand.Intn(screenWidth-w), rand.Intn(screenHeight-h)
                vx, vy := 2*rand.Intn(2)-1, 2*rand.Intn(2)-1
                a := rand.Intn(maxAngle)
                sprites.sprites[i] = &Sprite{
                        imageWidth:  w,
                        imageHeight: h,
                        x:           x,
                        y:           y,
                        vx:          vx,
                        vy:          vy,
                        angle:       a,
                }
        }
}

func update(screen *ebiten.Image) error {
        // Decrease the nubmer of the sprites.
        if ebiten.IsKeyPressed(ebiten.KeyLeft) {
                sprites.num -= 20
                if sprites.num < MinSprites {
                        sprites.num = MinSprites
                }
        }

        // Increase the nubmer of the sprites.
        if ebiten.IsKeyPressed(ebiten.KeyRight) {
                sprites.num += 20
                if MaxSprites < sprites.num {
                        sprites.num = MaxSprites
                }
        }

        sprites.Update()

        if ebiten.IsRunningSlowly() {
                return nil
        }

        // Draw each sprite.
        // DrawImage can be called many many times, but in the implementation,
        // the actual draw call to GPU is very few since these calls satisfy
        // some conditions e.g. all the rendering sources and targets are same.
        // For more detail, see:
        // https://godoc.org/github.com/hajimehoshi/ebiten#Image.DrawImage
        w, h := ebitenImage.Size()
        for i := 0; i < sprites.num; i++ {
                s := sprites.sprites[i]
                op.GeoM.Reset()
                op.GeoM.Translate(-float64(w)/2, -float64(h)/2)
                op.GeoM.Rotate(2 * math.Pi * float64(s.angle) / maxAngle)
                op.GeoM.Translate(float64(w)/2, float64(h)/2)
                op.GeoM.Translate(float64(s.x), float64(s.y))
                screen.DrawImage(ebitenImage, op)
        }
        msg := fmt.Sprintf(`FPS: %0.2f
Num of sprites: %d
Press <- or -> to change the number of sprites`, ebiten.CurrentFPS(), sprites.num)
        ebitenutil.DebugPrint(screen, msg)
        return nil
}

func main() {
        if err := ebiten.Run(update, screenWidth, screenHeight, 2, "Sprites (Ebiten Demo)"); err != nil {
                log.Fatal(err)
        }
}