// SPDX-License-Identifier: Unlicense OR MIT

package gpu

import (
	"image"
	"time"
)

// Backend represents the abstraction of underlying GPU
// APIs such as OpenGL, Direct3D useful for rendering Gio
// operations.
type Backend 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)
	DefaultFramebuffer() Framebuffer
	NewFramebuffer(tex Texture, depthBits int) (Framebuffer, error)
	NewImmutableBuffer(typ BufferBinding, data []byte) (Buffer, error)
	NewBuffer(typ BufferBinding, size int) (Buffer, error)
	NewProgram(vertexShader, fragmentShader ShaderSources) (Program, error)
	NewInputLayout(vertexShader ShaderSources, layout []InputDesc) (InputLayout, error)

	DepthFunc(f DepthFunc)
	ClearColor(r, g, b, a float32)
	ClearDepth(d float32)
	Clear(buffers BufferAttachments)
	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)
}

type ShaderSources struct {
	GLES2       string
	HLSL        []byte
	Uniforms    []UniformLocation
	UniformSize int
	Inputs      []InputLocation
	Textures    []TextureBinding
}

type TextureBinding 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 {
	Bind()
	Release()
}

type BlendFactor uint8

type DrawMode uint8

type BufferAttachments uint

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 {
	Bind()
	Release()
	SetVertexUniforms(buf Buffer)
	SetFragmentUniforms(buf Buffer)
}

type Buffer interface {
	BindVertex(stride, offset int)
	BindIndex()
	Release()
	Upload(data []byte)
}

type Framebuffer interface {
	Bind()
	Invalidate()
	Release()
}

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

type Texture interface {
	Upload(img *image.RGBA)
	Release()
	Bind(unit int)
}

const (
	BufferAttachmentColor BufferAttachments = 1 << iota
	BufferAttachmentDepth
)

const (
	DepthFuncGreater DepthFunc = iota
)

const (
	DataTypeFloat DataType = iota
	DataTypeShort
)

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

const (
	TextureFormatSRGB TextureFormat = iota
	TextureFormatFloat
)

const (
	FilterNearest TextureFilter = iota
	FilterLinear
)

const (
	FeatureTimers Features = iota
)

const (
	DrawModeTriangleStrip DrawMode = iota
	DrawModeTriangles
)

const (
	BlendFactorOne BlendFactor = iota
	BlendFactorOneMinusSrcAlpha
	BlendFactorZero
	BlendFactorDstColor
)

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