// Copyright 2016 Hajime Hoshi
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package opengl

import (
	"errors"
	"fmt"
	"sync"
	"unsafe"

	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver"
	"github.com/hajimehoshi/ebiten/v2/internal/graphicsdriver/opengl/gl"
	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
)

type blendFactor int

const (
	glDstAlpha         blendFactor = 0x304
	glDstColor         blendFactor = 0x306
	glOne              blendFactor = 1
	glOneMinusDstAlpha blendFactor = 0x305
	glOneMinusDstColor blendFactor = 0x307
	glOneMinusSrcAlpha blendFactor = 0x303
	glOneMinusSrcColor blendFactor = 0x301
	glSrcAlpha         blendFactor = 0x302
	glSrcAlphaSaturate blendFactor = 0x308
	glSrcColor         blendFactor = 0x300
	glZero             blendFactor = 0
)

type blendOperation int

const (
	glFuncAdd             blendOperation = 0x8006
	glFuncReverseSubtract blendOperation = 0x800b
	glFuncSubtract        blendOperation = 0x800a
)

func convertBlendFactor(f graphicsdriver.BlendFactor) blendFactor {
	switch f {
	case graphicsdriver.BlendFactorZero:
		return glZero
	case graphicsdriver.BlendFactorOne:
		return glOne
	case graphicsdriver.BlendFactorSourceColor:
		return glSrcColor
	case graphicsdriver.BlendFactorOneMinusSourceColor:
		return glOneMinusSrcColor
	case graphicsdriver.BlendFactorSourceAlpha:
		return glSrcAlpha
	case graphicsdriver.BlendFactorOneMinusSourceAlpha:
		return glOneMinusSrcAlpha
	case graphicsdriver.BlendFactorDestinationColor:
		return glDstColor
	case graphicsdriver.BlendFactorOneMinusDestinationColor:
		return glOneMinusDstColor
	case graphicsdriver.BlendFactorDestinationAlpha:
		return glDstAlpha
	case graphicsdriver.BlendFactorOneMinusDestinationAlpha:
		return glOneMinusDstAlpha
	case graphicsdriver.BlendFactorSourceAlphaSaturated:
		return glSrcAlphaSaturate
	default:
		panic(fmt.Sprintf("opengl: invalid blend factor %d", f))
	}
}

func convertBlendOperation(o graphicsdriver.BlendOperation) blendOperation {
	switch o {
	case graphicsdriver.BlendOperationAdd:
		return glFuncAdd
	case graphicsdriver.BlendOperationSubtract:
		return glFuncSubtract
	case graphicsdriver.BlendOperationReverseSubtract:
		return glFuncReverseSubtract
	default:
		panic(fmt.Sprintf("opengl: invalid blend operation %d", o))
	}
}

type (
	textureNative      uint32
	renderbufferNative uint32
	framebufferNative  uint32
	shader             uint32
	program            uint32
	buffer             uint32
)

type (
	uniformLocation int32
	attribLocation  int32
)

const (
	invalidFramebuffer = (1 << 32) - 1
	invalidUniform     = -1
)

type context struct {
	ctx gl.Context

	locationCache      *locationCache
	screenFramebuffer  framebufferNative // This might not be the default frame buffer '0' (e.g. iOS).
	lastFramebuffer    framebufferNative
	lastTexture        textureNative
	lastRenderbuffer   renderbufferNative
	lastViewportWidth  int
	lastViewportHeight int
	lastBlend          graphicsdriver.Blend
	maxTextureSize     int
	maxTextureSizeOnce sync.Once
	highp              bool
	highpOnce          sync.Once
	initOnce           sync.Once

	contextPlatform
}

func (c *context) bindTexture(t textureNative) {
	if c.lastTexture == t {
		return
	}
	c.ctx.BindTexture(gl.TEXTURE_2D, uint32(t))
	c.lastTexture = t
}

func (c *context) bindRenderbuffer(r renderbufferNative) {
	if c.lastRenderbuffer == r {
		return
	}
	c.ctx.BindRenderbuffer(gl.RENDERBUFFER, uint32(r))
	c.lastRenderbuffer = r
}

func (c *context) bindFramebuffer(f framebufferNative) {
	if c.lastFramebuffer == f {
		return
	}
	c.ctx.BindFramebuffer(gl.FRAMEBUFFER, uint32(f))
	c.lastFramebuffer = f
}

func (c *context) setViewport(f *framebuffer) {
	c.bindFramebuffer(f.native)
	if c.lastViewportWidth == f.width && c.lastViewportHeight == f.height {
		return
	}

	// On some environments, viewport size must be within the framebuffer size.
	// e.g. Edge (#71), Chrome on GPD Pocket (#420), macOS Mojave (#691).
	// Use the same size of the framebuffer here.
	c.ctx.Viewport(0, 0, int32(f.width), int32(f.height))

	// glViewport must be called at least at every frame on iOS.
	// As the screen framebuffer is the last render target, next SetViewport should be
	// the first call at a frame.
	if f.native == c.screenFramebuffer {
		c.lastViewportWidth = 0
		c.lastViewportHeight = 0
	} else {
		c.lastViewportWidth = f.width
		c.lastViewportHeight = f.height
	}
}

func (c *context) newScreenFramebuffer(width, height int) *framebuffer {
	return &framebuffer{
		native: c.screenFramebuffer,
		width:  width,
		height: height,
	}
}

func (c *context) getMaxTextureSize() int {
	c.maxTextureSizeOnce.Do(func() {
		c.maxTextureSize = c.ctx.GetInteger(gl.MAX_TEXTURE_SIZE)
	})
	return c.maxTextureSize
}

func (c *context) reset() error {
	var err1 error
	c.initOnce.Do(func() {
		// Load OpenGL functions after WGL is initialized especially for Windows (#2452).
		if err := c.ctx.LoadFunctions(); err != nil {
			err1 = err
			return
		}
	})
	if err1 != nil {
		return err1
	}

	c.locationCache = newLocationCache()
	c.lastTexture = 0
	c.lastFramebuffer = invalidFramebuffer
	c.lastViewportWidth = 0
	c.lastViewportHeight = 0
	c.lastBlend = graphicsdriver.Blend{}

	c.ctx.Enable(gl.BLEND)
	c.ctx.Enable(gl.SCISSOR_TEST)
	c.blend(graphicsdriver.BlendSourceOver)
	c.screenFramebuffer = framebufferNative(c.ctx.GetInteger(gl.FRAMEBUFFER_BINDING))
	// TODO: Need to update screenFramebufferWidth/Height?
	return nil
}

func (c *context) blend(blend graphicsdriver.Blend) {
	if c.lastBlend == blend {
		return
	}
	c.lastBlend = blend
	c.ctx.BlendFuncSeparate(
		uint32(convertBlendFactor(blend.BlendFactorSourceRGB)),
		uint32(convertBlendFactor(blend.BlendFactorDestinationRGB)),
		uint32(convertBlendFactor(blend.BlendFactorSourceAlpha)),
		uint32(convertBlendFactor(blend.BlendFactorDestinationAlpha)),
	)
	c.ctx.BlendEquationSeparate(
		uint32(convertBlendOperation(blend.BlendOperationRGB)),
		uint32(convertBlendOperation(blend.BlendOperationAlpha)),
	)
}

func (c *context) newTexture(width, height int) (textureNative, error) {
	t := c.ctx.CreateTexture()
	if t <= 0 {
		return 0, errors.New("opengl: creating texture failed")
	}
	c.bindTexture(textureNative(t))

	c.ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST)
	c.ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST)
	c.ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)
	c.ctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE)
	c.ctx.PixelStorei(gl.UNPACK_ALIGNMENT, 4)

	// Firefox warns the usage of textures without specifying pixels (#629)
	//
	//     Error: WebGL warning: drawElements: This operation requires zeroing texture data. This is slow.
	//
	// In Ebitengine, textures are filled with pixels later by the filter that ignores destination, so it is fine
	// to leave textures as uninitialized here. Rather, extra memory allocating for initialization should be
	// avoided.
	c.ctx.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, int32(width), int32(height), gl.RGBA, gl.UNSIGNED_BYTE, nil)

	return textureNative(t), nil
}

func (c *context) framebufferPixels(buf []byte, f *framebuffer, x, y, width, height int) error {
	if got, want := len(buf), 4*width*height; got != want {
		return fmt.Errorf("opengl: len(buf) must be %d but was %d at framebufferPixels", got, want)
	}

	c.ctx.Flush()
	c.bindFramebuffer(f.native)
	c.ctx.ReadPixels(buf, int32(x), int32(y), int32(width), int32(height), gl.RGBA, gl.UNSIGNED_BYTE)
	return nil
}

func (c *context) framebufferPixelsToBuffer(f *framebuffer, buffer buffer, width, height int) {
	c.ctx.Flush()

	c.bindFramebuffer(f.native)

	c.ctx.BindBuffer(gl.PIXEL_PACK_BUFFER, uint32(buffer))
	c.ctx.ReadPixels(nil, 0, 0, int32(width), int32(height), gl.RGBA, gl.UNSIGNED_BYTE)
	c.ctx.BindBuffer(gl.PIXEL_PACK_BUFFER, 0)
}

func (c *context) deleteTexture(t textureNative) {
	if !c.ctx.IsTexture(uint32(t)) {
		return
	}
	if c.lastTexture == t {
		c.lastTexture = 0
	}
	c.ctx.DeleteTexture(uint32(t))
}

func (c *context) newRenderbuffer(width, height int) (renderbufferNative, error) {
	r := c.ctx.CreateRenderbuffer()
	if r <= 0 {
		return 0, errors.New("opengl: creating renderbuffer failed")
	}

	renderbuffer := renderbufferNative(r)
	c.bindRenderbuffer(renderbuffer)

	var stencilFormat uint32
	if c.ctx.IsES() {
		// https://docs.gl/es2/glRenderbufferStorage
		// > Must be one of the following symbolic constants: GL_RGBA4, GL_RGB565, GL_RGB5_A1,
		// > GL_DEPTH_COMPONENT16, or GL_STENCIL_INDEX8.
		//
		// https://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/renderbufferStorage
		// > A GLenum specifying the internal format of the renderbuffer. Possible values:
		// > * gl.RGBA4: 4 red bits, 4 green bits, 4 blue bits 4 alpha bits.
		// > * gl.RGB565: 5 red bits, 6 green bits, 5 blue bits.
		// > * gl.RGB5_A1: 5 red bits, 5 green bits, 5 blue bits, 1 alpha bit.
		// > * gl.DEPTH_COMPONENT16: 16 depth bits.
		// > * gl.STENCIL_INDEX8: 8 stencil bits.
		// > * gl.DEPTH_STENCIL
		stencilFormat = gl.STENCIL_INDEX8
	} else {
		// GL_STENCIL_INDEX8 might not be available with OpenGL 2.1.
		// https://www.khronos.org/opengl/wiki/Image_Format
		// > There are only 2 depth/stencil formats, each providing 8 stencil bits: GL_DEPTH24_STENCIL8 and GL_DEPTH32F_STENCIL8.
		// > [...]
		// > Stencil formats can only be used for Textures if OpenGL 4.4 or ARB_texture_stencil8 is available.
		stencilFormat = gl.DEPTH24_STENCIL8
	}
	c.ctx.RenderbufferStorage(gl.RENDERBUFFER, stencilFormat, int32(width), int32(height))

	return renderbuffer, nil
}

func (c *context) deleteRenderbuffer(r renderbufferNative) {
	if !c.ctx.IsRenderbuffer(uint32(r)) {
		return
	}
	if c.lastRenderbuffer == r {
		c.lastRenderbuffer = 0
	}
	c.ctx.DeleteRenderbuffer(uint32(r))
}

func (c *context) newFramebuffer(texture textureNative, width, height int) (*framebuffer, error) {
	f := c.ctx.CreateFramebuffer()
	if f <= 0 {
		return nil, fmt.Errorf("opengl: creating framebuffer failed: the returned value is not positive but %d", f)
	}
	c.bindFramebuffer(framebufferNative(f))

	c.ctx.FramebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, uint32(texture), 0)
	if s := c.ctx.CheckFramebufferStatus(gl.FRAMEBUFFER); s != gl.FRAMEBUFFER_COMPLETE {
		if s != 0 {
			return nil, fmt.Errorf("opengl: creating framebuffer failed: %v", s)
		}
		if e := c.ctx.GetError(); e != gl.NO_ERROR {
			return nil, fmt.Errorf("opengl: creating framebuffer failed: (glGetError) %d", e)
		}
		return nil, fmt.Errorf("opengl: creating framebuffer failed: unknown error")
	}
	return &framebuffer{
		native: framebufferNative(f),
		width:  width,
		height: height,
	}, nil
}

func (c *context) bindStencilBuffer(f framebufferNative, r renderbufferNative) error {
	c.bindFramebuffer(f)

	c.ctx.FramebufferRenderbuffer(gl.FRAMEBUFFER, gl.STENCIL_ATTACHMENT, gl.RENDERBUFFER, uint32(r))
	if s := c.ctx.CheckFramebufferStatus(gl.FRAMEBUFFER); s != gl.FRAMEBUFFER_COMPLETE {
		return errors.New(fmt.Sprintf("opengl: glFramebufferRenderbuffer failed: %d", s))
	}
	return nil
}

func (c *context) deleteFramebuffer(f framebufferNative) {
	if f == c.screenFramebuffer {
		return
	}
	if !c.ctx.IsFramebuffer(uint32(f)) {
		return
	}
	// If a framebuffer to be deleted is bound, a newly bound framebuffer
	// will be a default framebuffer.
	// https://www.khronos.org/opengles/sdk/docs/man/xhtml/glDeleteFramebuffers.xml
	if c.lastFramebuffer == f {
		c.lastFramebuffer = invalidFramebuffer
		c.lastViewportWidth = 0
		c.lastViewportHeight = 0
	}
	c.ctx.DeleteFramebuffer(uint32(f))
}

func (c *context) newShader(shaderType uint32, source string) (shader, error) {
	s := c.ctx.CreateShader(shaderType)
	if s == 0 {
		return 0, fmt.Errorf("opengl: glCreateShader failed: shader type: %d", shaderType)
	}

	c.ctx.ShaderSource(s, source)
	c.ctx.CompileShader(s)

	if c.ctx.GetShaderi(s, gl.COMPILE_STATUS) == gl.FALSE {
		log := c.ctx.GetShaderInfoLog(s)
		return 0, fmt.Errorf("opengl: shader compile failed: %s", log)
	}
	return shader(s), nil
}

func (c *context) newProgram(shaders []shader, attributes []string) (program, error) {
	p := c.ctx.CreateProgram()
	if p == 0 {
		return 0, errors.New("opengl: glCreateProgram failed")
	}

	for _, shader := range shaders {
		c.ctx.AttachShader(p, uint32(shader))
	}

	for i, name := range attributes {
		c.ctx.BindAttribLocation(p, uint32(i), name)
	}

	c.ctx.LinkProgram(p)
	if c.ctx.GetProgrami(p, gl.LINK_STATUS) == gl.FALSE {
		info := c.ctx.GetProgramInfoLog(p)
		return 0, fmt.Errorf("opengl: program error: %s", info)
	}
	return program(p), nil
}

func (c *context) deleteProgram(p program) {
	c.locationCache.deleteProgram(p)

	if !c.ctx.IsProgram(uint32(p)) {
		return
	}
	c.ctx.DeleteProgram(uint32(p))
}

func (c *context) uniformInt(p program, location string, v int) bool {
	l := c.locationCache.GetUniformLocation(c, p, location)
	if l == invalidUniform {
		return false
	}
	c.ctx.Uniform1i(int32(l), int32(v))
	return true
}

func (c *context) uniforms(p program, location string, v []uint32, typ shaderir.Type) bool {
	l := c.locationCache.GetUniformLocation(c, p, location)
	if l == invalidUniform {
		return false
	}

	base := typ.Main
	if base == shaderir.Array {
		base = typ.Sub[0].Main
	}

	switch base {
	case shaderir.Float:
		c.ctx.Uniform1fv(int32(l), uint32sToFloat32s(v))
	case shaderir.Int:
		c.ctx.Uniform1iv(int32(l), uint32sToInt32s(v))
	case shaderir.Vec2:
		c.ctx.Uniform2fv(int32(l), uint32sToFloat32s(v))
	case shaderir.Vec3:
		c.ctx.Uniform3fv(int32(l), uint32sToFloat32s(v))
	case shaderir.Vec4:
		c.ctx.Uniform4fv(int32(l), uint32sToFloat32s(v))
	case shaderir.Mat2:
		c.ctx.UniformMatrix2fv(int32(l), uint32sToFloat32s(v))
	case shaderir.Mat3:
		c.ctx.UniformMatrix3fv(int32(l), uint32sToFloat32s(v))
	case shaderir.Mat4:
		c.ctx.UniformMatrix4fv(int32(l), uint32sToFloat32s(v))
	default:
		panic(fmt.Sprintf("opengl: unexpected type: %s", typ.String()))
	}
	return true
}

func (c *context) newArrayBuffer(size int) buffer {
	b := c.ctx.CreateBuffer()
	c.ctx.BindBuffer(gl.ARRAY_BUFFER, b)
	c.ctx.BufferInit(gl.ARRAY_BUFFER, size, gl.DYNAMIC_DRAW)
	return buffer(b)
}

func (c *context) newElementArrayBuffer(size int) buffer {
	b := c.ctx.CreateBuffer()
	c.ctx.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, b)
	c.ctx.BufferInit(gl.ELEMENT_ARRAY_BUFFER, size, gl.DYNAMIC_DRAW)
	return buffer(b)
}

func (c *context) arrayBufferSubData(data []float32) {
	s := unsafe.Slice((*byte)(unsafe.Pointer(&data[0])), len(data)*4)
	c.ctx.BufferSubData(gl.ARRAY_BUFFER, 0, s)
}

func (c *context) elementArrayBufferSubData(data []uint16) {
	s := unsafe.Slice((*byte)(unsafe.Pointer(&data[0])), len(data)*2)
	c.ctx.BufferSubData(gl.ELEMENT_ARRAY_BUFFER, 0, s)
}