// Copyright 2022 The Ebitengine Authors
//
// 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 colorm

import (
	"fmt"
	"image/color"
	"sync"

	"github.com/hajimehoshi/ebiten/v2"
	"github.com/hajimehoshi/ebiten/v2/internal/affine"
	"github.com/hajimehoshi/ebiten/v2/internal/colormshader"
)

// Dim is the dimension of a ColorM.
const Dim = affine.ColorMDim

// ColorM represents a matrix to transform coloring when rendering an image. The matrix
// is applied by a fragment shader to each pixel during the rendering process.
//
// ColorM is applied to the straight alpha color
// while an Image's pixels' format is alpha premultiplied.
// Before applying a matrix, a color is un-multiplied, and after applying the matrix,
// the color is multiplied again.
// The pixel input and output are expected to be r,g,b,a values in the range 0 to 1.

// The initial value is identity.
type ColorM struct {
	impl affine.ColorM

	_ [0]func() // Marks as non-comparable.
}

func (c *ColorM) affineColorM() affine.ColorM {
	if c.impl != nil {
		return c.impl
	}
	return affine.ColorMIdentity{}
}

// String returns a string representation of ColorM.
func (c *ColorM) String() string {
	return c.affineColorM().String()
}

// Reset resets the ColorM as identity.
func (c *ColorM) Reset() {
	c.impl = affine.ColorMIdentity{}
}

// Apply pre-multiplies a vector (r, g, b, a, 1) by the matrix
// where r, g, b, and a are clr's values in straight-alpha format.
// In other words, Apply calculates ColorM * (r, g, b, a, 1)^T.
func (c *ColorM) Apply(clr color.Color) color.Color {
	return c.affineColorM().Apply(clr)
}

// Concat multiplies a color matrix with the other color matrix.
// This is same as multiplying the matrix other and the matrix c in this order.
func (c *ColorM) Concat(other ColorM) {
	o := other.impl
	if o == nil {
		return
	}
	c.impl = c.affineColorM().Concat(o)
}

// Scale scales the matrix by (r, g, b, a).
func (c *ColorM) Scale(r, g, b, a float64) {
	c.impl = c.affineColorM().Scale(float32(r), float32(g), float32(b), float32(a))
}

// ScaleWithColor scales the matrix by clr.
func (c *ColorM) ScaleWithColor(clr color.Color) {
	cr, cg, cb, ca := clr.RGBA()
	if ca == 0 {
		c.Scale(0, 0, 0, 0)
		return
	}
	c.Scale(float64(cr)/float64(ca), float64(cg)/float64(ca), float64(cb)/float64(ca), float64(ca)/0xffff)
}

// Translate translates the matrix by (r, g, b, a).
func (c *ColorM) Translate(r, g, b, a float64) {
	c.impl = c.affineColorM().Translate(float32(r), float32(g), float32(b), float32(a))
}

// RotateHue rotates the hue.
// theta represents rotating angle in radian.
func (c *ColorM) RotateHue(theta float64) {
	c.ChangeHSV(theta, 1, 1)
}

// ChangeHSV changes HSV (Hue-Saturation-Value) values.
// hueTheta is a radian value to rotate hue.
// saturationScale is a value to scale saturation.
// valueScale is a value to scale value (a.k.a. brightness).
//
// This conversion uses RGB to/from YCrCb conversion.
func (c *ColorM) ChangeHSV(hueTheta float64, saturationScale float64, valueScale float64) {
	c.impl = affine.ChangeHSV(c.affineColorM(), hueTheta, float32(saturationScale), float32(valueScale))
}

// Element returns a value of a matrix at (i, j).
func (c *ColorM) Element(i, j int) float64 {
	return float64(c.affineColorM().At(i, j))
}

// SetElement sets an element at (i, j).
func (c *ColorM) SetElement(i, j int, element float64) {
	c.impl = affine.ColorMSetElement(c.affineColorM(), i, j, float32(element))
}

// IsInvertible returns a boolean value indicating
// whether the matrix c is invertible or not.
func (c *ColorM) IsInvertible() bool {
	return c.affineColorM().IsInvertible()
}

// Invert inverts the matrix.
// If c is not invertible, Invert panics.
func (c *ColorM) Invert() {
	c.impl = c.affineColorM().Invert()
}

// ReadElements reads the body part and the translation part to the given float32 slices.
//
// len(body) must be 16 and len(translation) must be 4. Otherwise, ReadElements panics.
func (c *ColorM) ReadElements(body []float32, translation []float32) {
	if len(body) != 16 {
		panic(fmt.Sprintf("ebiten: len(body) must be 16 but %d", len(body)))
	}
	if len(translation) != 4 {
		panic(fmt.Sprintf("ebiten: len(translation) must be 4 but %d", len(translation)))
	}
	c.affineColorM().Elements(body, translation)
}

func uniforms(c ColorM) map[string]any {
	var body [16]float32
	var translation [4]float32
	c.affineColorM().Elements(body[:], translation[:])

	uniforms := map[string]any{}
	uniforms[colormshader.UniformColorMBody] = body[:]
	uniforms[colormshader.UniformColorMTranslation] = translation[:]
	return uniforms
}

type builtinShaderKey struct {
	filter  colormshader.Filter
	address colormshader.Address
}

var (
	builtinShaders  = map[builtinShaderKey]*ebiten.Shader{}
	builtinShadersM sync.Mutex
)

func builtinShader(filter colormshader.Filter, address colormshader.Address) *ebiten.Shader {
	builtinShadersM.Lock()
	defer builtinShadersM.Unlock()

	key := builtinShaderKey{
		filter:  filter,
		address: address,
	}
	if s, ok := builtinShaders[key]; ok {
		return s
	}

	src := colormshader.ShaderSource(filter, address)
	s, err := ebiten.NewShader(src)
	if err != nil {
		panic(fmt.Sprintf("colorm: NewShader for a built-in shader failed: %v", err))
	}
	shader := s

	builtinShaders[key] = shader
	return shader
}
