// 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(minFilter, magFilter TextureFilter) Texture
	DefaultFramebuffer() Framebuffer
	NilTexture() Texture
	NewFramebuffer() Framebuffer
	NewBuffer(typ BufferType) Buffer
	NewProgram(vertexShader, fragmentShader string, attribMap []string) (Program, error)
	SetupVertexArray(slot int, size int, dataType DataType, stride, offset int)

	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 BlendFactor uint8

type DrawMode uint8

type BufferAttachments uint

type TextureFilter uint8
type TextureFormat uint8

type BufferType uint8
type BufferUsage uint8

type DataType uint8

type DepthFunc uint8

type Features uint

type Caps struct {
	Features       Features
	MaxTextureSize int
}

type Program interface {
	Bind()
	Release()
	UniformFor(uniform string) Uniform
	Uniform1i(u Uniform, v int)
	Uniform1f(u Uniform, v float32)
	Uniform2f(u Uniform, v0, v1 float32)
	Uniform4f(u Uniform, v0, v1, v2, v3 float32)
}

type Uniform interface{}

type Buffer interface {
	Bind()
	Upload(usage BufferUsage, data []byte)
	Release()
}

type Framebuffer interface {
	Bind()
	BindTexture(t Texture)
	Invalidate()
	Release()
	IsComplete() error
}

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

type Texture interface {
	Upload(img *image.RGBA)
	Release()
	Bind(unit int)
	Resize(format TextureFormat, width, height int)
}

const (
	BufferAttachmentColor BufferAttachments = 1 << iota
	BufferAttachmentDepth
)

const (
	DepthFuncGreater DepthFunc = iota
)

const (
	DataTypeFloat DataType = iota
	DataTypeShort
)

const (
	BufferUsageStaticDraw BufferUsage = iota
)

const (
	BufferTypeIndices BufferType = iota
	BufferTypeData
)

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
}