// Provides a [color.Color] type for dealing with OkLab colours without alpha.
package oklab

import (
	"image/color"
	"math"

	"smariot.com/color/internal/helper"
)

// Color is an OkLab [color.Color].
type Color struct {
	Lightness, ChromaA, ChromaB float64
}

// DistanceSqr returns the euclidean distance squared between two colours.
func DistanceSqr(a, b Color) float64 {
	dLightness := a.Lightness - b.Lightness
	dChromaA := a.ChromaA - b.ChromaA
	dChromaB := a.ChromaB - b.ChromaB
	return dLightness*dLightness + dChromaA*dChromaA + dChromaB*dChromaB
}

// Distance returns the euclidean distance between two colours,
//
// If you just want to compare relative distances, use [DistanceSqr] instead.
func Distance(a, b Color) float64 {
	return math.Sqrt(DistanceSqr(a, b))
}

// RGBA converts to premultiplied RGBA, implementing the [color.Color] interface.
func (c Color) RGBA() (r, g, b, a uint32) {
	r, g, b = helper.LRGBtoRGB(helper.LMStoLRGB(helper.OkLabToLMS(c.Lightness, c.ChromaA, c.ChromaB)))
	a = 0xffff
	return
}

// NRGBA converts to non-premultiplied RGBA.
func (c Color) NRGBA() (r, g, b, a uint32) {
	r, g, b = helper.LRGBtoRGB(helper.LMStoLRGB(helper.OkLabToLMS(c.Lightness, c.ChromaA, c.ChromaB)))
	a = 0xffff
	return
}

// NLRGBA converts to non-premultiplied linear RGBA.
func (c Color) NLRGBA() (r, g, b, a float64) {
	r, g, b = helper.LMStoLRGB(helper.OkLabToLMS(c.Lightness, c.ChromaA, c.ChromaB))
	a = 1
	return
}

// NXYZA converts to non-premultiplied XYZ+Alpha.
func (c Color) NXYZA() (x, y, z, a float64) {
	x, y, z = helper.LMStoXYZ(helper.OkLabToLMS(c.Lightness, c.ChromaA, c.ChromaB))
	return x, y, z, 1
}

// NOkLabA converts to non-premultiplied OkLab+Alpha.
func (c Color) NOkLabA() (lightness, chromaA, chromaB, a float64) {
	return c.Lightness, c.ChromaA, c.ChromaB, 1
}

// Convert converts an arbitrary colour type to an OkLab [Color].
func Convert(c color.Color) Color {
	if c, ok := c.(Color); ok {
		return c
	}

	lightness, chromaA, chromaB, _ := helper.ColorToNOkLabA(c)
	return Color{lightness, chromaA, chromaB}
}

// A [color.Model] for converting arbitrary colours to an OkLab [Color].
//
// Wraps the [Convert] function, returning a [color.Color] interface rather than the [Color] type.
var Model = helper.Model(Convert)

// Type assertion.
var _ color.Color = Color{}