package opengl

import (
	"fmt"
	"github.com/go-gl/gl"
	"github.com/hajimehoshi/ebiten/graphics/opengl/internal/shader"
)

func orthoProjectionMatrix(left, right, bottom, top int) [4][4]float64 {
	e11 := float64(2) / float64(right-left)
	e22 := float64(2) / float64(top-bottom)
	e14 := -1 * float64(right+left) / float64(right-left)
	e24 := -1 * float64(top+bottom) / float64(top-bottom)

	return [4][4]float64{
		{e11, 0, 0, e14},
		{0, e22, 0, e24},
		{0, 0, 1, 0},
		{0, 0, 0, 1},
	}
}

type RenderTarget struct {
	framebuffer gl.Framebuffer
	width       int
	height      int
	flipY       bool
}

func createFramebuffer(nativeTexture gl.Texture) gl.Framebuffer {
	framebuffer := gl.GenFramebuffer()
	framebuffer.Bind()

	gl.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0,
		gl.TEXTURE_2D, nativeTexture, 0)
	if gl.CheckFramebufferStatus(gl.FRAMEBUFFER) != gl.FRAMEBUFFER_COMPLETE {
		panic("creating framebuffer failed")
	}

	// Set this framebuffer opaque because alpha values on a target might be
	// confusing.
	gl.ClearColor(0, 0, 0, 1)
	gl.Clear(gl.COLOR_BUFFER_BIT)

	return framebuffer
}

func (r *RenderTarget) setAsViewport() {
	gl.Flush()
	r.framebuffer.Bind()
	err := gl.CheckFramebufferStatus(gl.FRAMEBUFFER)
	if err != gl.FRAMEBUFFER_COMPLETE {
		panic(fmt.Sprintf("glBindFramebuffer failed: %d", err))
	}

	gl.BlendFuncSeparate(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA, gl.ZERO, gl.ONE)

	width := shader.AdjustSizeForTexture(r.width)
	height := shader.AdjustSizeForTexture(r.height)
	gl.Viewport(0, 0, width, height)
}

func (r *RenderTarget) projectionMatrix() [4][4]float64 {
	width := shader.AdjustSizeForTexture(r.width)
	height := shader.AdjustSizeForTexture(r.height)
	matrix := orthoProjectionMatrix(0, width, 0, height)
	if r.flipY {
		matrix[1][1] *= -1
		matrix[1][3] += float64(r.height) / float64(shader.AdjustSizeForTexture(r.height)) * 2
	}
	return matrix
}

func (r *RenderTarget) dispose() {
	r.framebuffer.Delete()
}