// +build example

package main

import (
        "fmt"
        _ "image/jpeg"
        "log"
        "math"

        "github.com/hajimehoshi/ebiten"
        "github.com/hajimehoshi/ebiten/ebitenutil"
)

const (
        screenWidth  = 320
        screenHeight = 240
)

var (
        hue128        = 0
        saturation128 = 128
        value128      = 128

        inverted = false

        prevPressedI = false
        gophersImage *ebiten.Image
)

// clamp clamps v to the range [min, max].
func clamp(v, min, max int) int {
        if min > max {
                panic("min must <= max")
        }
        if v < min {
                return min
        }
        if max < v {
                return max
        }
        return v
}

func update(screen *ebiten.Image) error {
        // Adjust HSV values along with the user's input.
        if ebiten.IsKeyPressed(ebiten.KeyQ) {
                hue128--
        }
        if ebiten.IsKeyPressed(ebiten.KeyW) {
                hue128++
        }
        if ebiten.IsKeyPressed(ebiten.KeyA) {
                saturation128--
        }
        if ebiten.IsKeyPressed(ebiten.KeyS) {
                saturation128++
        }
        if ebiten.IsKeyPressed(ebiten.KeyZ) {
                value128--
        }
        if ebiten.IsKeyPressed(ebiten.KeyX) {
                value128++
        }

        hue128 = clamp(hue128, -256, 256)
        saturation128 = clamp(saturation128, 0, 256)
        value128 = clamp(value128, 0, 256)

        pressedI := ebiten.IsKeyPressed(ebiten.KeyI)
        if pressedI && !prevPressedI {
                inverted = !inverted
        }
        prevPressedI = pressedI

        if ebiten.IsRunningSlowly() {
                return nil
        }

        // Center the image on the screen.
        w, h := gophersImage.Size()
        op := &ebiten.DrawImageOptions{}
        op.GeoM.Translate(float64(screenWidth-w)/2, float64(screenHeight-h)/2)

        // Change HSV.
        hue := float64(hue128) * 2 * math.Pi / 128
        saturation := float64(saturation128) / 128
        value := float64(value128) / 128
        op.ColorM.ChangeHSV(hue, saturation, value)

        // Invert the color.
        if inverted {
                op.ColorM.Scale(-1, -1, -1, 1)
                op.ColorM.Translate(1, 1, 1, 0)
        }

        screen.DrawImage(gophersImage, op)

        // Draw the text of the current status.
        msgInverted := "false"
        if inverted {
                msgInverted = "true"
        }
        msg := fmt.Sprintf(`Hue:        %0.2f [Q][W]
Saturation: %0.2f [A][S]
Value:      %0.2f [Z][X]
Inverted:   %s [I]`, hue, saturation, value, msgInverted)
        ebitenutil.DebugPrint(screen, msg)
        return nil
}

func main() {
        var err error
        gophersImage, _, err = ebitenutil.NewImageFromFile("_resources/images/gophers.jpg", ebiten.FilterDefault)
        if err != nil {
                log.Fatal(err)
        }
        if err := ebiten.Run(update, screenWidth, screenHeight, 2, "HSV (Ebiten Demo)"); err != nil {
                log.Fatal(err)
        }
}