// SPDX-License-Identifier: Unlicense OR MIT

package backend

import (
	"image"
	"time"
)

// Device represents the abstraction of underlying GPU
// APIs such as OpenGL, Direct3D useful for rendering Gio
// operations.
type Device interface {
	BeginFrame()
	EndFrame()
	Caps() Caps
	NewTimer() Timer
	// IsContinuousTime reports whether all timer measurements
	// are valid at the point of call.
	IsTimeContinuous() bool
	NewTexture(format TextureFormat, width, height int, minFilter, magFilter TextureFilter, bindings BufferBinding) (Texture, error)
	CurrentFramebuffer() Framebuffer
	NewFramebuffer(tex Texture, depthBits int) (Framebuffer, error)
	NewImmutableBuffer(typ BufferBinding, data []byte) (Buffer, error)
	NewBuffer(typ BufferBinding, size int) (Buffer, error)
	NewComputeProgram(shader ShaderSources) (Program, error)
	NewProgram(vertexShader, fragmentShader ShaderSources) (Program, error)
	NewInputLayout(vertexShader ShaderSources, layout []InputDesc) (InputLayout, error)

	DepthFunc(f DepthFunc)
	ClearDepth(d float32)
	Clear(r, g, b, a float32)
	Viewport(x, y, width, height int)
	DrawArrays(mode DrawMode, off, count int)
	DrawElements(mode DrawMode, off, count int)
	SetBlend(enable bool)
	SetDepthTest(enable bool)
	DepthMask(mask bool)
	BlendFunc(sfactor, dfactor BlendFactor)

	BindInputLayout(i InputLayout)
	BindProgram(p Program)
	BindFramebuffer(f Framebuffer)
	BindTexture(unit int, t Texture)
	BindVertexBuffer(b Buffer, stride, offset int)
	BindIndexBuffer(b Buffer)
	BindImageTexture(unit int, texture Texture, access AccessBits, format TextureFormat)

	MemoryBarrier()
	DispatchCompute(x, y, z int)
}

type ShaderSources struct {
	Name           string
	GLSL100ES      string
	GLSL300ES      string
	GLSL310ES      string
	GLSL130        string
	GLSL150        string
	HLSL           []byte
	Uniforms       UniformsReflection
	Inputs         []InputLocation
	Textures       []TextureBinding
	StorageBuffers []StorageBufferBinding
}

type StorageBufferBinding struct {
	Binding   int
	BlockSize int
}

type UniformsReflection struct {
	Blocks    []UniformBlock
	Locations []UniformLocation
	Size      int
}

type TextureBinding struct {
	Name    string
	Binding int
}

type UniformBlock struct {
	Name    string
	Binding int
}

type UniformLocation struct {
	Name   string
	Type   DataType
	Size   int
	Offset int
}

type InputLocation struct {
	// For GLSL.
	Name     string
	Location int
	// For HLSL.
	Semantic      string
	SemanticIndex int

	Type DataType
	Size int
}

// InputDesc describes a vertex attribute as laid out in a Buffer.
type InputDesc struct {
	Type DataType
	Size int

	Offset int
}

// InputLayout is the backend specific representation of the mapping
// between Buffers and shader attributes.
type InputLayout interface {
	Release()
}

type AccessBits uint8

type BlendFactor uint8

type DrawMode uint8

type TextureFilter uint8
type TextureFormat uint8

type BufferBinding uint8

type DataType uint8

type DepthFunc uint8

type Features uint

type Caps struct {
	Features       Features
	MaxTextureSize int
}

type Program interface {
	Release()
	SetStorageBuffer(binding int, buf Buffer)
	SetVertexUniforms(buf Buffer)
	SetFragmentUniforms(buf Buffer)
}

type Buffer interface {
	Release()
	Upload(data []byte)
	Download(data []byte) error
}

type Framebuffer interface {
	Invalidate()
	Release()
	ReadPixels(src image.Rectangle, pixels []byte) error
}

type Timer interface {
	Begin()
	End()
	Duration() (time.Duration, bool)
	Release()
}

type Texture interface {
	Upload(offset, size image.Point, pixels []byte)
	Release()
}

const (
	DepthFuncGreater DepthFunc = iota
	DepthFuncGreaterEqual
)

const (
	DataTypeFloat DataType = iota
	DataTypeInt
	DataTypeShort
)

const (
	BufferBindingIndices BufferBinding = 1 << iota
	BufferBindingVertices
	BufferBindingUniforms
	BufferBindingTexture
	BufferBindingFramebuffer
	BufferBindingShaderStorage
)

const (
	TextureFormatSRGB TextureFormat = iota
	TextureFormatFloat
	TextureFormatRGBA8
)

const (
	AccessRead AccessBits = 1 + iota
	AccessWrite
)

const (
	FilterNearest TextureFilter = iota
	FilterLinear
)

const (
	FeatureTimers Features = 1 << iota
	FeatureFloatRenderTargets
	FeatureCompute
)

const (
	DrawModeTriangleStrip DrawMode = iota
	DrawModeTriangles
)

const (
	BlendFactorOne BlendFactor = iota
	BlendFactorOneMinusSrcAlpha
	BlendFactorZero
	BlendFactorDstColor
)

func (f Features) Has(feats Features) bool {
	return f&feats == feats
}

func UploadImage(t Texture, offset image.Point, img *image.RGBA) {
	var pixels []byte
	size := img.Bounds().Size()
	if img.Stride != size.X*4 {
		panic("unsupported stride")
	}
	start := img.PixOffset(0, 0)
	end := img.PixOffset(size.X, size.Y-1)
	pixels = img.Pix[start:end]
	t.Upload(offset, size, pixels)
}