package imgui

import (
	"errors"
	"fmt"
	"image"

	"github.com/go-gl/gl/v3.2-core/gl"
)

// OpenGL3 implements a renderer based on github.com/go-gl/gl (v3.2-core).
type OpenGL3 struct {
	imguiIO IO

	glslVersion            string
	fontTexture            uint32
	shaderHandle           uint32
	vertHandle             uint32
	fragHandle             uint32
	attribLocationTex      int32
	attribLocationProjMtx  int32
	attribLocationPosition int32
	attribLocationUV       int32
	attribLocationColor    int32
	vboHandle              uint32
	elementsHandle         uint32

	contentScale     float32
	textureMinFilter int32
	textureMagFilter int32
}

// Texture filtering types.
const (
	textureFilterNearest = iota
	textureFilterLinear
	textureFilterNearestMipmapNearest
	textureFilterLinearMipmapNearest
	textureFilterNearestMipmapLinear
	textureFilterLinearMipmapLinear
)

// NewOpenGL3 attempts to initialize a renderer.
// An OpenGL context has to be established before calling this function.
func NewOpenGL3(io IO, contentScale float32) (*OpenGL3, error) {
	err := gl.Init()
	if err != nil {
		return nil, fmt.Errorf("failed to initialize OpenGL: %v", err)
	}

	renderer := &OpenGL3{
		imguiIO:          io,
		glslVersion:      "#version 150",
		contentScale:     contentScale,
		textureMinFilter: gl.LINEAR,
		textureMagFilter: gl.LINEAR,
	}
	renderer.createDeviceObjects()
	return renderer, nil
}

// Dispose cleans up the resources.
func (renderer *OpenGL3) Dispose() {
	renderer.invalidateDeviceObjects()
}

// PreRender clears the framebuffer.
func (renderer *OpenGL3) PreRender(clearColor [4]float32) {
	gl.ClearColor(clearColor[0], clearColor[1], clearColor[2], clearColor[3])
	gl.Clear(gl.COLOR_BUFFER_BIT)
}

// Render translates the ImGui draw data to OpenGL3 commands.
func (renderer *OpenGL3) Render(displaySize [2]float32, framebufferSize [2]float32, drawData DrawData) {
	// Avoid rendering when minimized, scale coordinates for retina displays (screen coordinates != framebuffer coordinates)
	displayWidth, displayHeight := displaySize[0], displaySize[1]
	fbWidth, fbHeight := framebufferSize[0], framebufferSize[1]
	if (fbWidth <= 0) || (fbHeight <= 0) {
		return
	}
	drawData.ScaleClipRects(Vec2{
		X: fbWidth / displayWidth,
		Y: fbHeight / displayHeight,
	})

	// Backup GL state
	var lastActiveTexture int32
	gl.GetIntegerv(gl.ACTIVE_TEXTURE, &lastActiveTexture)
	gl.ActiveTexture(gl.TEXTURE0)
	var lastProgram int32
	gl.GetIntegerv(gl.CURRENT_PROGRAM, &lastProgram)
	var lastTexture int32
	gl.GetIntegerv(gl.TEXTURE_BINDING_2D, &lastTexture)
	var lastSampler int32
	gl.GetIntegerv(gl.SAMPLER_BINDING, &lastSampler)
	var lastArrayBuffer int32
	gl.GetIntegerv(gl.ARRAY_BUFFER_BINDING, &lastArrayBuffer)
	var lastElementArrayBuffer int32
	gl.GetIntegerv(gl.ELEMENT_ARRAY_BUFFER_BINDING, &lastElementArrayBuffer)
	var lastVertexArray int32
	gl.GetIntegerv(gl.VERTEX_ARRAY_BINDING, &lastVertexArray)
	var lastPolygonMode [2]int32
	gl.GetIntegerv(gl.POLYGON_MODE, &lastPolygonMode[0])
	var lastViewport [4]int32
	gl.GetIntegerv(gl.VIEWPORT, &lastViewport[0])
	var lastScissorBox [4]int32
	gl.GetIntegerv(gl.SCISSOR_BOX, &lastScissorBox[0])
	var lastBlendSrcRgb int32
	gl.GetIntegerv(gl.BLEND_SRC_RGB, &lastBlendSrcRgb)
	var lastBlendDstRgb int32
	gl.GetIntegerv(gl.BLEND_DST_RGB, &lastBlendDstRgb)
	var lastBlendSrcAlpha int32
	gl.GetIntegerv(gl.BLEND_SRC_ALPHA, &lastBlendSrcAlpha)
	var lastBlendDstAlpha int32
	gl.GetIntegerv(gl.BLEND_DST_ALPHA, &lastBlendDstAlpha)
	var lastBlendEquationRgb int32
	gl.GetIntegerv(gl.BLEND_EQUATION_RGB, &lastBlendEquationRgb)
	var lastBlendEquationAlpha int32
	gl.GetIntegerv(gl.BLEND_EQUATION_ALPHA, &lastBlendEquationAlpha)
	lastEnableBlend := gl.IsEnabled(gl.BLEND)
	lastEnableCullFace := gl.IsEnabled(gl.CULL_FACE)
	lastEnableDepthTest := gl.IsEnabled(gl.DEPTH_TEST)
	lastEnableScissorTest := gl.IsEnabled(gl.SCISSOR_TEST)

	// Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, polygon fill
	gl.Enable(gl.BLEND)
	gl.BlendEquation(gl.FUNC_ADD)
	gl.BlendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA)
	gl.Disable(gl.CULL_FACE)
	gl.Disable(gl.DEPTH_TEST)
	gl.Enable(gl.SCISSOR_TEST)
	gl.PolygonMode(gl.FRONT_AND_BACK, gl.FILL)

	// Setup viewport, orthographic projection matrix
	// Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right).
	// DisplayMin is typically (0,0) for single viewport apps.
	gl.Viewport(0, 0, int32(fbWidth), int32(fbHeight))
	orthoProjection := [4][4]float32{
		{2.0 / displayWidth, 0.0, 0.0, 0.0},
		{0.0, 2.0 / -displayHeight, 0.0, 0.0},
		{0.0, 0.0, -1.0, 0.0},
		{-1.0, 1.0, 0.0, 1.0},
	}
	gl.UseProgram(renderer.shaderHandle)
	gl.Uniform1i(renderer.attribLocationTex, 0)
	gl.UniformMatrix4fv(renderer.attribLocationProjMtx, 1, false, &orthoProjection[0][0])
	gl.BindSampler(0, 0) // Rely on combined texture/sampler state.

	// Recreate the VAO every time
	// (This is to easily allow multiple GL contexts. VAO are not shared among GL contexts, and
	// we don't track creation/deletion of windows so we don't have an obvious key to use to cache them.)
	var vaoHandle uint32
	gl.GenVertexArrays(1, &vaoHandle)
	gl.BindVertexArray(vaoHandle)
	gl.BindBuffer(gl.ARRAY_BUFFER, renderer.vboHandle)
	gl.EnableVertexAttribArray(uint32(renderer.attribLocationPosition))
	gl.EnableVertexAttribArray(uint32(renderer.attribLocationUV))
	gl.EnableVertexAttribArray(uint32(renderer.attribLocationColor))
	vertexSize, vertexOffsetPos, vertexOffsetUv, vertexOffsetCol := VertexBufferLayout()
	gl.VertexAttribPointerWithOffset(uint32(renderer.attribLocationPosition), 2, gl.FLOAT, false, int32(vertexSize), uintptr(vertexOffsetPos))
	gl.VertexAttribPointerWithOffset(uint32(renderer.attribLocationUV), 2, gl.FLOAT, false, int32(vertexSize), uintptr(vertexOffsetUv))
	gl.VertexAttribPointerWithOffset(uint32(renderer.attribLocationColor), 4, gl.UNSIGNED_BYTE, true, int32(vertexSize), uintptr(vertexOffsetCol))
	indexSize := IndexBufferLayout()
	drawType := gl.UNSIGNED_SHORT
	if indexSize == 4 {
		drawType = gl.UNSIGNED_INT
	}

	// Draw
	for _, list := range drawData.CommandLists() {
		// var indexBufferOffset uintptr

		vertexBuffer, vertexBufferSize := list.VertexBuffer()
		gl.BindBuffer(gl.ARRAY_BUFFER, renderer.vboHandle)
		gl.BufferData(gl.ARRAY_BUFFER, vertexBufferSize, vertexBuffer, gl.STREAM_DRAW)

		indexBuffer, indexBufferSize := list.IndexBuffer()
		gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, renderer.elementsHandle)
		gl.BufferData(gl.ELEMENT_ARRAY_BUFFER, indexBufferSize, indexBuffer, gl.STREAM_DRAW)

		for _, cmd := range list.Commands() {
			if cmd.HasUserCallback() {
				cmd.CallUserCallback(list)
			} else {
				gl.BindTexture(gl.TEXTURE_2D, uint32(cmd.TextureID()))
				gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, renderer.textureMinFilter) // minification filter
				gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, renderer.textureMagFilter) // magnification filter
				clipRect := cmd.ClipRect()
				gl.Scissor(int32(clipRect.X), int32(fbHeight)-int32(clipRect.W), int32(clipRect.Z-clipRect.X), int32(clipRect.W-clipRect.Y))
				gl.DrawElementsBaseVertexWithOffset(gl.TRIANGLES, int32(cmd.ElementCount()), uint32(drawType),
					uintptr(cmd.IdxOffset()*uint(indexSize)), int32(cmd.VertexOffset()))
			}
			// indexBufferOffset += uintptr(cmd.ElementCount() * indexSize)
		}
	}
	gl.DeleteVertexArrays(1, &vaoHandle)

	// Restore modified GL state
	gl.UseProgram(uint32(lastProgram))
	gl.BindTexture(gl.TEXTURE_2D, uint32(lastTexture))
	gl.BindSampler(0, uint32(lastSampler))
	gl.ActiveTexture(uint32(lastActiveTexture))
	gl.BindVertexArray(uint32(lastVertexArray))
	gl.BindBuffer(gl.ARRAY_BUFFER, uint32(lastArrayBuffer))
	gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, uint32(lastElementArrayBuffer))
	gl.BlendEquationSeparate(uint32(lastBlendEquationRgb), uint32(lastBlendEquationAlpha))
	gl.BlendFuncSeparate(uint32(lastBlendSrcRgb), uint32(lastBlendDstRgb), uint32(lastBlendSrcAlpha), uint32(lastBlendDstAlpha))
	if lastEnableBlend {
		gl.Enable(gl.BLEND)
	} else {
		gl.Disable(gl.BLEND)
	}
	if lastEnableCullFace {
		gl.Enable(gl.CULL_FACE)
	} else {
		gl.Disable(gl.CULL_FACE)
	}
	if lastEnableDepthTest {
		gl.Enable(gl.DEPTH_TEST)
	} else {
		gl.Disable(gl.DEPTH_TEST)
	}
	if lastEnableScissorTest {
		gl.Enable(gl.SCISSOR_TEST)
	} else {
		gl.Disable(gl.SCISSOR_TEST)
	}
	gl.PolygonMode(gl.FRONT_AND_BACK, uint32(lastPolygonMode[0]))
	gl.Viewport(lastViewport[0], lastViewport[1], lastViewport[2], lastViewport[3])
	gl.Scissor(lastScissorBox[0], lastScissorBox[1], lastScissorBox[2], lastScissorBox[3])
}

func (renderer *OpenGL3) createDeviceObjects() {
	// Backup GL state
	var lastTexture int32
	var lastArrayBuffer int32
	var lastVertexArray int32
	gl.GetIntegerv(gl.TEXTURE_BINDING_2D, &lastTexture)
	gl.GetIntegerv(gl.ARRAY_BUFFER_BINDING, &lastArrayBuffer)
	gl.GetIntegerv(gl.VERTEX_ARRAY_BINDING, &lastVertexArray)

	vertexShader := renderer.glslVersion + `
uniform mat4 ProjMtx;
in vec2 Position;
in vec2 UV;
in vec4 Color;
out vec2 Frag_UV;
out vec4 Frag_Color;
void main()
{
	Frag_UV = UV;
	Frag_Color = Color;
	gl_Position = ProjMtx * vec4(Position.xy,0,1);
}
`
	fragmentShader := renderer.glslVersion + `
uniform sampler2D Texture;
in vec2 Frag_UV;
in vec4 Frag_Color;
out vec4 Out_Color;
void main()
{
	Out_Color = Frag_Color * texture(Texture, Frag_UV);
}
`
	renderer.shaderHandle = gl.CreateProgram()
	renderer.vertHandle = gl.CreateShader(gl.VERTEX_SHADER)
	renderer.fragHandle = gl.CreateShader(gl.FRAGMENT_SHADER)

	glShaderSource := func(handle uint32, source string) {
		csource, free := gl.Strs(source + "\x00")
		defer free()

		gl.ShaderSource(handle, 1, csource, nil)
	}

	glShaderSource(renderer.vertHandle, vertexShader)
	glShaderSource(renderer.fragHandle, fragmentShader)
	gl.CompileShader(renderer.vertHandle)
	gl.CompileShader(renderer.fragHandle)
	gl.AttachShader(renderer.shaderHandle, renderer.vertHandle)
	gl.AttachShader(renderer.shaderHandle, renderer.fragHandle)
	gl.LinkProgram(renderer.shaderHandle)

	renderer.attribLocationTex = gl.GetUniformLocation(renderer.shaderHandle, gl.Str("Texture"+"\x00"))
	renderer.attribLocationProjMtx = gl.GetUniformLocation(renderer.shaderHandle, gl.Str("ProjMtx"+"\x00"))
	renderer.attribLocationPosition = gl.GetAttribLocation(renderer.shaderHandle, gl.Str("Position"+"\x00"))
	renderer.attribLocationUV = gl.GetAttribLocation(renderer.shaderHandle, gl.Str("UV"+"\x00"))
	renderer.attribLocationColor = gl.GetAttribLocation(renderer.shaderHandle, gl.Str("Color"+"\x00"))

	gl.GenBuffers(1, &renderer.vboHandle)
	gl.GenBuffers(1, &renderer.elementsHandle)

	// Restore modified GL state
	gl.BindTexture(gl.TEXTURE_2D, uint32(lastTexture))
	gl.BindBuffer(gl.ARRAY_BUFFER, uint32(lastArrayBuffer))
	gl.BindVertexArray(uint32(lastVertexArray))
}

func (renderer *OpenGL3) SetFontTexture(image *RGBA32Image) {
	// Delete old font texture
	if renderer.fontTexture != 0 {
		gl.DeleteTextures(1, &renderer.fontTexture)
		CurrentIO().Fonts().SetTextureID(0)
		renderer.fontTexture = 0
	}

	// Upload texture to graphics system
	var lastTexture int32
	gl.GetIntegerv(gl.TEXTURE_BINDING_2D, &lastTexture)
	gl.GenTextures(1, &renderer.fontTexture)
	gl.BindTexture(gl.TEXTURE_2D, renderer.fontTexture)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)
	gl.PixelStorei(gl.UNPACK_ROW_LENGTH, 0)
	gl.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, int32(image.Width), int32(image.Height), 0, gl.RGBA, gl.UNSIGNED_BYTE, image.Pixels)

	// Store our identifier
	CurrentIO().Fonts().SetTextureID(TextureID(renderer.fontTexture))

	// Restore state
	gl.BindTexture(gl.TEXTURE_2D, uint32(lastTexture))
}

func (renderer *OpenGL3) invalidateDeviceObjects() {
	if renderer.vboHandle != 0 {
		gl.DeleteBuffers(1, &renderer.vboHandle)
	}
	renderer.vboHandle = 0
	if renderer.elementsHandle != 0 {
		gl.DeleteBuffers(1, &renderer.elementsHandle)
	}
	renderer.elementsHandle = 0

	if (renderer.shaderHandle != 0) && (renderer.vertHandle != 0) {
		gl.DetachShader(renderer.shaderHandle, renderer.vertHandle)
	}
	if renderer.vertHandle != 0 {
		gl.DeleteShader(renderer.vertHandle)
	}
	renderer.vertHandle = 0

	if (renderer.shaderHandle != 0) && (renderer.fragHandle != 0) {
		gl.DetachShader(renderer.shaderHandle, renderer.fragHandle)
	}
	if renderer.fragHandle != 0 {
		gl.DeleteShader(renderer.fragHandle)
	}
	renderer.fragHandle = 0

	if renderer.shaderHandle != 0 {
		gl.DeleteProgram(renderer.shaderHandle)
	}
	renderer.shaderHandle = 0

	if renderer.fontTexture != 0 {
		gl.DeleteTextures(1, &renderer.fontTexture)
		CurrentIO().Fonts().SetTextureID(0)
		renderer.fontTexture = 0
	}
}

// SetTextureMinFilter sets the minifying function for texture filtering.
func (renderer *OpenGL3) SetTextureMinFilter(min uint) error {
	switch min {
	case textureFilterNearest:
		renderer.textureMinFilter = gl.NEAREST
	case textureFilterLinear:
		renderer.textureMinFilter = gl.LINEAR
	case textureFilterNearestMipmapNearest:
		renderer.textureMinFilter = gl.NEAREST_MIPMAP_NEAREST
	case textureFilterLinearMipmapNearest:
		renderer.textureMinFilter = gl.LINEAR_MIPMAP_NEAREST
	case textureFilterNearestMipmapLinear:
		renderer.textureMinFilter = gl.NEAREST_MIPMAP_LINEAR
	case textureFilterLinearMipmapLinear:
		renderer.textureMinFilter = gl.LINEAR_MIPMAP_LINEAR
	default:
		return errors.New("invalid minifying filter")
	}

	return nil
}

// SetTextureMagFilter sets the magnifying function for texture filtering.
func (renderer *OpenGL3) SetTextureMagFilter(mag uint) error {
	switch mag {
	case textureFilterNearest:
		renderer.textureMagFilter = gl.NEAREST
	case textureFilterLinear:
		renderer.textureMagFilter = gl.LINEAR
	default:
		return fmt.Errorf("invalid magnifying filter")
	}
	return nil
}

// Load image and return the TextureID
func (renderer *OpenGL3) LoadImage(image *image.RGBA) (TextureID, error) {
	texture, err := renderer.createImageTexture(image)
	if err != nil {
		return 0, err
	}

	return texture, nil
}

func (renderer *OpenGL3) ReleaseImage(textureId TextureID) {
	gl.BindTexture(gl.TEXTURE_2D, 0)
	handle := uint32(textureId)
	gl.DeleteTextures(1, &handle)
}

func (renderer *OpenGL3) createImageTexture(img *image.RGBA) (TextureID, error) {
	// Upload texture to graphics system
	var lastTexture int32
	var handle uint32
	gl.GetIntegerv(gl.TEXTURE_BINDING_2D, &lastTexture)
	gl.GenTextures(1, &handle)
	gl.BindTexture(gl.TEXTURE_2D, handle)
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR) // minification filter
	gl.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR) // magnification filter
	gl.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, int32(img.Bounds().Dx()), int32(img.Bounds().Dy()), 0, gl.RGBA, gl.UNSIGNED_BYTE, gl.Ptr(img.Pix))
	gl.GenerateMipmap(gl.TEXTURE_2D)

	// Restore state
	gl.BindTexture(gl.TEXTURE_2D, uint32(lastTexture))

	return TextureID(handle), nil
}