package opengl

// #cgo LDFLAGS: -framework OpenGL
//
// #include <OpenGL/gl.h>
import "C"
import (
	"github.com/hajimehoshi/go-ebiten/graphics"
	"image"
	"unsafe"
)

func nextPowerOf2(x uint64) uint64 {
	x -= 1
	x |= (x >> 1)
	x |= (x >> 2)
	x |= (x >> 4)
	x |= (x >> 8)
	x |= (x >> 16)
	x |= (x >> 32)
	return x + 1
}

func adjustPixels(width, height int, pixels []uint8) []uint8 {
	textureWidth := int(nextPowerOf2(uint64(width)))
	textureHeight := int(nextPowerOf2(uint64(height)))
	if width == textureWidth && height == textureHeight {
		return pixels
	}

	newPixels := make([]uint8, textureWidth*textureHeight*4)

	for j := 0; j < height; j++ {
		copy(newPixels[textureWidth*4*j:],
			pixels[width*4*j:width*4*j+width*4])
	}
	return newPixels
}

type Texture struct {
	id            graphics.TextureID
	native        C.GLuint
	width         int
	height        int
	textureWidth  int
	textureHeight int
}

type RenderTarget struct {
	id          graphics.RenderTargetID
	texture     *Texture
	framebuffer C.GLuint
}

func (texture *Texture) ID() graphics.TextureID {
	return texture.id
}

func createTexture(width, height int, pixels []uint8) *Texture {
	if pixels != nil {
		pixels = adjustPixels(width, height, pixels)
	}
	textureWidth := int(nextPowerOf2(uint64(width)))
	textureHeight := int(nextPowerOf2(uint64(height)))
	texture := &Texture{
		id:            0,
		width:         width,
		height:        height,
		textureWidth:  textureWidth,
		textureHeight: textureHeight,
	}

	nativeTexture := C.GLuint(0)
	C.glGenTextures(1, (*C.GLuint)(&nativeTexture))
	if nativeTexture < 0 {
		panic("glGenTexture failed")
	}
	C.glPixelStorei(C.GL_UNPACK_ALIGNMENT, 4)
	C.glBindTexture(C.GL_TEXTURE_2D, C.GLuint(nativeTexture))

	ptr := unsafe.Pointer(nil)
	if pixels != nil {
		ptr = unsafe.Pointer(&pixels[0])
	}
	C.glTexImage2D(C.GL_TEXTURE_2D, 0, C.GL_RGBA,
		C.GLsizei(textureWidth), C.GLsizei(textureHeight),
		0, C.GL_RGBA, C.GL_UNSIGNED_BYTE, ptr)

	C.glTexParameteri(C.GL_TEXTURE_2D, C.GL_TEXTURE_MAG_FILTER, C.GL_LINEAR)
	C.glTexParameteri(C.GL_TEXTURE_2D, C.GL_TEXTURE_MIN_FILTER, C.GL_LINEAR)
	C.glBindTexture(C.GL_TEXTURE_2D, 0)

	texture.native = nativeTexture

	texture.id = graphics.TextureID(<-newID)

	return texture
}

func newRenderTarget(width, height int) *RenderTarget {
	texture := createTexture(width, height, nil)
	framebuffer := createFramebuffer(texture.native)
	return &RenderTarget{
		id:          graphics.RenderTargetID(<-newID),
		texture:     texture,
		framebuffer: framebuffer,
	}
}

func (renderTarget *RenderTarget) ID() graphics.RenderTargetID {
	return renderTarget.id
}

func (renderTarget *RenderTarget) Texture() *Texture {
	return renderTarget.texture
}

type textureError string

func (err textureError) Error() string {
	return "Texture Error: " + string(err)
}

func newTextureFromImage(img image.Image) (*Texture, error) {
	var pix []uint8
	switch img.(type) {
	case *image.RGBA:
		pix = img.(*image.RGBA).Pix
	case *image.NRGBA:
		pix = img.(*image.NRGBA).Pix
	default:
		return nil, textureError("image format must be RGBA or NRGBA")
	}
	size := img.Bounds().Size()
	return createTexture(size.X, size.Y, pix), nil
}

func newRenderTargetWithFramebuffer(width, height int,
	framebuffer C.GLuint) *RenderTarget {
	texture := &Texture{
		id:            graphics.TextureID(<-newID),
		width:         width,
		height:        height,
		textureWidth:  int(nextPowerOf2(uint64(width))),
		textureHeight: int(nextPowerOf2(uint64(height))),
	}
	return &RenderTarget{
		texture:     texture,
		framebuffer: framebuffer,
	}
}

func createFramebuffer(nativeTexture C.GLuint) C.GLuint {
	framebuffer := C.GLuint(0)
	C.glGenFramebuffers(1, &framebuffer)

	origFramebuffer := C.GLint(0)
	C.glGetIntegerv(C.GL_FRAMEBUFFER_BINDING, &origFramebuffer)
	C.glBindFramebuffer(C.GL_FRAMEBUFFER, framebuffer)
	C.glFramebufferTexture2D(C.GL_FRAMEBUFFER, C.GL_COLOR_ATTACHMENT0,
		C.GL_TEXTURE_2D, nativeTexture, 0)
	C.glBindFramebuffer(C.GL_FRAMEBUFFER, C.GLuint(origFramebuffer))
	if C.glCheckFramebufferStatus(C.GL_FRAMEBUFFER) !=
		C.GL_FRAMEBUFFER_COMPLETE {
		panic("creating framebuffer failed")
	}

	return framebuffer
}

var newID chan int

func init() {
	newID = make(chan int)
	go func() {
		for i := 0; ; i++ {
			newID <- i
		}
	}()
}