package photos

import (
	"encoding/json"
	"errors"
	"math"
	"sort"
)

// Edit parameters are stored in the photo metadata and describe a
// non-destructive render: the original object is never touched, the edited
// image is produced as a separate object.

// LightParams holds the parameters of the "Свет" (light) tool. The slider
// ranges mirror the ones Lightroom exposes: exposure in stops, everything else
// in percent.
type LightParams struct {
	Exposure   float64 `json:"exposure"`
	Contrast   float64 `json:"contrast"`
	Highlights float64 `json:"highlights"`
	Shadows    float64 `json:"shadows"`
	Whites     float64 `json:"whites"`
	Blacks     float64 `json:"blacks"`
	Curve      CurveParams `json:"curve"`
}

// CurveParams holds one tone curve per channel. An empty channel means the
// identity (linear) curve.
type CurveParams struct {
	RGB   []CurvePoint `json:"rgb,omitempty"`
	Red   []CurvePoint `json:"red,omitempty"`
	Green []CurvePoint `json:"green,omitempty"`
	Blue  []CurvePoint `json:"blue,omitempty"`
}

// CurvePoint is a control point of a tone curve, in the 0..1 range.
type CurvePoint struct {
	X float64 `json:"x"`
	Y float64 `json:"y"`
}

// ColorParams holds the parameters of the "Цвет" (color) tool: white balance,
// vibrance/saturation, the per-hue color mixer, color grading and a simple
// per-channel color correction. Percent values use -100..100, wheel hues use
// 0..360.
type ColorParams struct {
	Temperature float64         `json:"temperature"`
	Tint        float64         `json:"tint"`
	Vibrance    float64         `json:"vibrance"`
	Saturation  float64         `json:"saturation"`
	Mixer       ColorMixer      `json:"mixer"`
	Grading     ColorGrading    `json:"grading"`
	Correction  ColorCorrection `json:"correction"`
}

// ColorMixer holds one HSL band per hue, mirroring the Lightroom color mixer.
type ColorMixer struct {
	Red     MixerBand `json:"red"`
	Orange  MixerBand `json:"orange"`
	Yellow  MixerBand `json:"yellow"`
	Green   MixerBand `json:"green"`
	Aqua    MixerBand `json:"aqua"`
	Blue    MixerBand `json:"blue"`
	Purple  MixerBand `json:"purple"`
	Magenta MixerBand `json:"magenta"`
}

// MixerBand is a hue/saturation/luminance adjustment of one color band.
type MixerBand struct {
	Hue        float64 `json:"hue"`
	Saturation float64 `json:"saturation"`
	Luminance  float64 `json:"luminance"`
}

// ColorGrading holds the three color-grading wheels and their blending.
type ColorGrading struct {
	Shadows    ColorWheel `json:"shadows"`
	Midtones   ColorWheel `json:"midtones"`
	Highlights ColorWheel `json:"highlights"`
	Blending   float64    `json:"blending"`
	Balance    float64    `json:"balance"`
}

// ColorWheel is a hue, strength and luminance used by color grading.
type ColorWheel struct {
	Hue        float64 `json:"hue"`
	Saturation float64 `json:"saturation"`
	Luminance  float64 `json:"luminance"`
}

// ColorCorrection is a simple per-channel gain, in percent.
type ColorCorrection struct {
	Red   float64 `json:"red"`
	Green float64 `json:"green"`
	Blue  float64 `json:"blue"`
}

// mixerBand is a color band with its hue center in degrees.
type mixerBand struct {
	center     float64
	hue        float64
	saturation float64
	luminance  float64
}

// bands returns the mixer bands in a stable order.
func (m ColorMixer) bands() [8]mixerBand {
	return [8]mixerBand{
		{0, m.Red.Hue, m.Red.Saturation, m.Red.Luminance},
		{30, m.Orange.Hue, m.Orange.Saturation, m.Orange.Luminance},
		{60, m.Yellow.Hue, m.Yellow.Saturation, m.Yellow.Luminance},
		{120, m.Green.Hue, m.Green.Saturation, m.Green.Luminance},
		{180, m.Aqua.Hue, m.Aqua.Saturation, m.Aqua.Luminance},
		{240, m.Blue.Hue, m.Blue.Saturation, m.Blue.Luminance},
		{280, m.Purple.Hue, m.Purple.Saturation, m.Purple.Luminance},
		{320, m.Magenta.Hue, m.Magenta.Saturation, m.Magenta.Luminance},
	}
}

// wheels returns the grading wheels in a stable order.
func (g ColorGrading) wheels() [3]ColorWheel {
	return [3]ColorWheel{g.Shadows, g.Midtones, g.Highlights}
}

// EditParams is the full set of non-destructive editing parameters of a photo.
type EditParams struct {
	Light LightParams `json:"light"`
	Color ColorParams `json:"color"`
}

// Limits of the editing parameters. They are enforced on write so a hand-made
// request can never push the renderer into an extreme state.
const (
	MaxExposureStops = 5.0
	MaxPercent       = 100.0
	MaxCurvePoints   = 16
)

// ErrInvalidEditParams is returned when the client sends unusable parameters.
var ErrInvalidEditParams = errors.New("invalid edit params")

// ParseEditParams decodes and normalizes the editing parameters sent by a
// client. Values outside the allowed range are clamped, and the curve points
// are sorted and de-duplicated.
func ParseEditParams(raw []byte) (EditParams, error) {
	var p EditParams
	if len(raw) == 0 {
		return p, nil
	}
	if err := json.Unmarshal(raw, &p); err != nil {
		return EditParams{}, ErrInvalidEditParams
	}
	p = p.Normalized()
	return p, nil
}

// Normalized returns a copy with every value clamped to the allowed range.
func (p EditParams) Normalized() EditParams {
	p.Light.Exposure = clampFloat(p.Light.Exposure, -MaxExposureStops, MaxExposureStops)
	p.Light.Contrast = clampFloat(p.Light.Contrast, -MaxPercent, MaxPercent)
	p.Light.Highlights = clampFloat(p.Light.Highlights, -MaxPercent, MaxPercent)
	p.Light.Shadows = clampFloat(p.Light.Shadows, -MaxPercent, MaxPercent)
	p.Light.Whites = clampFloat(p.Light.Whites, -MaxPercent, MaxPercent)
	p.Light.Blacks = clampFloat(p.Light.Blacks, -MaxPercent, MaxPercent)
	p.Light.Curve.RGB = normalizeCurve(p.Light.Curve.RGB)
	p.Light.Curve.Red = normalizeCurve(p.Light.Curve.Red)
	p.Light.Curve.Green = normalizeCurve(p.Light.Curve.Green)
	p.Light.Curve.Blue = normalizeCurve(p.Light.Curve.Blue)
	p.Color = p.Color.Normalized()
	return p
}

// Normalized returns a copy of the color parameters clamped to their ranges.
func (c ColorParams) Normalized() ColorParams {
	c.Temperature = clampFloat(c.Temperature, -MaxPercent, MaxPercent)
	c.Tint = clampFloat(c.Tint, -MaxPercent, MaxPercent)
	c.Vibrance = clampFloat(c.Vibrance, -MaxPercent, MaxPercent)
	c.Saturation = clampFloat(c.Saturation, -MaxPercent, MaxPercent)

	bands := c.Mixer.bands()
	for i := range bands {
		bands[i].hue = clampFloat(bands[i].hue, -MaxPercent, MaxPercent)
		bands[i].saturation = clampFloat(bands[i].saturation, -MaxPercent, MaxPercent)
		bands[i].luminance = clampFloat(bands[i].luminance, -MaxPercent, MaxPercent)
	}
	c.Mixer = ColorMixer{
		Red:     MixerBand{bands[0].hue, bands[0].saturation, bands[0].luminance},
		Orange:  MixerBand{bands[1].hue, bands[1].saturation, bands[1].luminance},
		Yellow:  MixerBand{bands[2].hue, bands[2].saturation, bands[2].luminance},
		Green:   MixerBand{bands[3].hue, bands[3].saturation, bands[3].luminance},
		Aqua:    MixerBand{bands[4].hue, bands[4].saturation, bands[4].luminance},
		Blue:    MixerBand{bands[5].hue, bands[5].saturation, bands[5].luminance},
		Purple:  MixerBand{bands[6].hue, bands[6].saturation, bands[6].luminance},
		Magenta: MixerBand{bands[7].hue, bands[7].saturation, bands[7].luminance},
	}

	wheels := c.Grading.wheels()
	for i := range wheels {
		wheels[i].Hue = clampFloat(wheels[i].Hue, 0, 360)
		wheels[i].Saturation = clampFloat(wheels[i].Saturation, -MaxPercent, MaxPercent)
		wheels[i].Luminance = clampFloat(wheels[i].Luminance, -MaxPercent, MaxPercent)
	}
	c.Grading = ColorGrading{
		Shadows:    wheels[0],
		Midtones:   wheels[1],
		Highlights: wheels[2],
		Blending:   clampFloat(c.Grading.Blending, 0, MaxPercent),
		Balance:    clampFloat(c.Grading.Balance, -MaxPercent, MaxPercent),
	}

	c.Correction.Red = clampFloat(c.Correction.Red, -MaxPercent, MaxPercent)
	c.Correction.Green = clampFloat(c.Correction.Green, -MaxPercent, MaxPercent)
	c.Correction.Blue = clampFloat(c.Correction.Blue, -MaxPercent, MaxPercent)
	return c
}

// IsEmpty reports whether the parameters describe an untouched photo.
func (p EditParams) IsEmpty() bool {
	l := p.Light
	if l.Exposure != 0 || l.Contrast != 0 || l.Highlights != 0 || l.Shadows != 0 ||
		l.Whites != 0 || l.Blacks != 0 {
		return false
	}
	for _, pts := range [][]CurvePoint{l.Curve.RGB, l.Curve.Red, l.Curve.Green, l.Curve.Blue} {
		for _, pt := range pts {
			if math.Abs(pt.X-pt.Y) > 1e-6 {
				return false
			}
		}
	}
	return p.Color.IsEmpty()
}

// IsEmpty reports whether the color parameters leave the image untouched.
func (c ColorParams) IsEmpty() bool {
	if c.Temperature != 0 || c.Tint != 0 || c.Vibrance != 0 || c.Saturation != 0 {
		return false
	}
	for _, b := range c.Mixer.bands() {
		if b.hue != 0 || b.saturation != 0 || b.luminance != 0 {
			return false
		}
	}
	for _, w := range c.Grading.wheels() {
		// A hue without strength or luminance has no effect.
		if w.Saturation != 0 || w.Luminance != 0 {
			return false
		}
	}
	return c.Correction.Red == 0 && c.Correction.Green == 0 && c.Correction.Blue == 0
}

// JSON encodes the parameters for storage in the photo metadata.
func (p EditParams) JSON() []byte {
	if p.IsEmpty() {
		return []byte("{}")
	}
	data, err := json.Marshal(p)
	if err != nil {
		return []byte("{}")
	}
	return data
}

// normalizeCurve clamps the points to the unit square, keeps them sorted by X
// and drops duplicates.
func normalizeCurve(points []CurvePoint) []CurvePoint {
	if len(points) == 0 {
		return nil
	}
	out := make([]CurvePoint, 0, len(points))
	for _, pt := range points {
		out = append(out, CurvePoint{
			X: clampFloat(pt.X, 0, 1),
			Y: clampFloat(pt.Y, 0, 1),
		})
	}
	sort.SliceStable(out, func(i, j int) bool { return out[i].X < out[j].X })
	deduped := out[:0]
	for i, pt := range out {
		if i > 0 && math.Abs(pt.X-deduped[len(deduped)-1].X) < 1e-6 {
			continue
		}
		deduped = append(deduped, pt)
	}
	if len(deduped) > MaxCurvePoints {
		deduped = deduped[:MaxCurvePoints]
	}
	return deduped
}

func clampFloat(v, min, max float64) float64 {
	if math.IsNaN(v) {
		return 0
	}
	if v < min {
		return min
	}
	if v > max {
		return max
	}
	return v
}

func clamp01(v float64) float64 {
	return clampFloat(v, 0, 1)
}

func clampInt(v, min, max int) int {
	if v < min {
		return min
	}
	if v > max {
		return max
	}
	return v
}

// curveLUT builds a 256-entry lookup table from the control points of a
// curve. The first and last points extend to the edges of the range, and the
// values in between are interpolated linearly.
func curveLUT(points []CurvePoint) [256]uint8 {
	var lut [256]uint8
	pts := normalizeCurve(points)
	if len(pts) < 2 {
		for i := range lut {
			lut[i] = uint8(i)
		}
		return lut
	}
	for i := 0; i < 256; i++ {
		x := float64(i) / 255
		lut[i] = uint8(math.Round(clamp01(curveEval(pts, x)) * 255))
	}
	return lut
}

// curveEval evaluates the curve at x using linear interpolation between the
// surrounding control points.
func curveEval(points []CurvePoint, x float64) float64 {
	if x <= points[0].X {
		return points[0].Y
	}
	last := points[len(points)-1]
	if x >= last.X {
		return last.Y
	}
	for i := 1; i < len(points); i++ {
		if x > points[i].X {
			continue
		}
		x0, y0 := points[i-1].X, points[i-1].Y
		x1, y1 := points[i].X, points[i].Y
		if x1-x0 < 1e-9 {
			return y1
		}
		t := (x - x0) / (x1 - x0)
		return y0 + t*(y1-y0)
	}
	return last.Y
}

// lightAdjuster holds the precomputed factors of the light adjustments. The
// factors are calculated once per render, so the per-pixel loop stays cheap.
type lightAdjuster struct {
	exposure   float64
	contrast   float64
	highlights float64
	shadows    float64
	whites     float64
	blacks     float64
}

func newLightAdjuster(p LightParams) lightAdjuster {
	return lightAdjuster{
		exposure:   math.Pow(2, p.Exposure),
		contrast:   1 + p.Contrast/100,
		highlights: p.Highlights / 100 * 80,
		shadows:    p.Shadows / 100 * 80,
		whites:     p.Whites / 100 * 80,
		blacks:     p.Blacks / 100 * 80,
	}
}

// apply maps a single channel value through the adjustments and the tone
// curves: the master curve first, the channel curve second. The order of the
// operations is fixed and mirrored by the client-side preview, so the live
// preview and the rendered result match.
func (a lightAdjuster) apply(v float64, master, channel *[256]uint8) float64 {
	// Экспозиция (стопы).
	v *= a.exposure
	// Контраст вокруг средней точки.
	v = 128 + (v-128)*a.contrast
	// Света: верхняя часть диапазона.
	w := clamp01((v - 128) / 127)
	v += a.highlights * w * w
	// Тени: нижняя часть диапазона.
	w = clamp01((128 - v) / 128)
	v += a.shadows * w * w
	// Белые: самый верх диапазона.
	w = clamp01((v - 192) / 63)
	v += a.whites * w
	// Чёрные: самый низ диапазона.
	w = clamp01((64 - v) / 64)
	v += a.blacks * w
	// Тоновая кривая: общая, затем канальная.
	idx := clampInt(int(v+0.5), 0, 255)
	v = float64(master[idx])
	idx = clampInt(int(v+0.5), 0, 255)
	return float64(channel[idx])
}

// adjustChannel applies the light adjustments to a single channel value. It
// is the per-pixel helper of the renderer.
func adjustChannel(v float64, p LightParams, master, channel *[256]uint8) float64 {
	return newLightAdjuster(p).apply(v, master, channel)
}

// rgbToHSL converts RGB (each 0..255) to HSL: hue in degrees, saturation and
// lightness in 0..1. It uses only arithmetic, so it is easy to mirror in the
// client and in the WASM module.
func rgbToHSL(r, g, b float64) (h, s, l float64) {
	r /= 255
	g /= 255
	b /= 255
	max := math.Max(r, math.Max(g, b))
	min := math.Min(r, math.Min(g, b))
	l = (max + min) / 2
	if max == min {
		return 0, 0, l
	}
	d := max - min
	if l > 0.5 {
		s = d / (2 - max - min)
	} else {
		s = d / (max + min)
	}
	switch max {
	case r:
		h = (g - b) / d
		if g < b {
			h += 6
		}
	case g:
		h = (b-r)/d + 2
	case b:
		h = (r-g)/d + 4
	}
	h *= 60
	return h, s, l
}

// hslToRGB converts HSL (hue in degrees, saturation and lightness in 0..1)
// back to RGB in 0..255.
func hslToRGB(h, s, l float64) (r, g, b float64) {
	if s == 0 {
		v := l * 255
		return v, v, v
	}
	var q float64
	if l < 0.5 {
		q = l * (1 + s)
	} else {
		q = l + s - l*s
	}
	p := 2*l - q
	hk := h / 360
	r = hueToRGB(p, q, hk+1.0/3)
	g = hueToRGB(p, q, hk)
	b = hueToRGB(p, q, hk-1.0/3)
	return r * 255, g * 255, b * 255
}

// hueToRGB is the per-channel helper of hslToRGB.
func hueToRGB(p, q, t float64) float64 {
	if t < 0 {
		t++
	}
	if t > 1 {
		t--
	}
	if t < 1.0/6 {
		return p + (q-p)*6*t
	}
	if t < 1.0/2 {
		return q
	}
	if t < 2.0/3 {
		return p + (q-p)*(2.0/3-t)*6
	}
	return p
}

// bandWeight returns a triangular weight of a hue around a band center.
func bandWeight(h, center float64) float64 {
	d := math.Abs(h - center)
	if d > 180 {
		d = 360 - d
	}
	return clamp01(1 - d/60)
}

// colorAdjuster holds the precomputed factors of the color adjustments. The
// order of the operations is fixed and mirrored by the client-side preview and
// the WASM module, so the live preview and the rendered result match.
type colorAdjuster struct {
	temperature float64
	tint        float64
	vibrance    float64
	saturation  float64
	mixer       [8]mixerBand
	hasMixer    bool
	wheels      [3]ColorWheel
	luminances  [3]float64
	blending    float64
	balance     float64
	correction  [3]float64
	tints       [3][3]float64
}

func newColorAdjuster(p ColorParams) colorAdjuster {
	a := colorAdjuster{
		temperature: p.Temperature / 100,
		tint:        p.Tint / 100,
		vibrance:    p.Vibrance / 100,
		saturation:  p.Saturation / 100,
		mixer:       p.Mixer.bands(),
		wheels:      p.Grading.wheels(),
		blending:    p.Grading.Blending / 100,
		balance:     p.Grading.Balance / 100,
		correction:  [3]float64{p.Correction.Red / 100, p.Correction.Green / 100, p.Correction.Blue / 100},
	}
	for _, band := range a.mixer {
		if band.hue != 0 || band.saturation != 0 || band.luminance != 0 {
			a.hasMixer = true
			break
		}
	}
	for i, wheel := range a.wheels {
		a.luminances[i] = wheel.Luminance / 100
		r, g, b := hslToRGB(wheel.Hue, 1, 0.5)
		a.tints[i] = [3]float64{r, g, b}
	}
	return a
}

// apply color-corrects one RGB pixel (each 0..255) and returns the result.
func (a colorAdjuster) apply(r, g, b float64) (float64, float64, float64) {
	// Баланс белого: тёплый/холодный и зелёный/пурпурный сдвиг.
	r *= 1 + 0.20*a.temperature + 0.10*a.tint
	g *= 1 - 0.20*a.tint
	b *= 1 - 0.20*a.temperature + 0.10*a.tint
	r = clampFloat(r, 0, 255)
	g = clampFloat(g, 0, 255)
	b = clampFloat(b, 0, 255)

	// Быстрый путь: только колёса/яркость, без микшера и насыщенности —
	// HSL-переход не нужен, lightness считается напрямую.
	fast := !a.hasMixer && a.saturation == 0 && a.vibrance == 0
	var weights [3]float64
	var rr, gg, bb float64

	if fast {
		max := math.Max(r, math.Max(g, b))
		min := math.Min(r, math.Min(g, b))
		l := (max + min) / 510
		lb := clamp01(l + a.balance*0.5)
		shadowW := (1 - lb) * (1 - lb)
		shadowW *= shadowW
		highlightW := lb * lb
		highlightW *= highlightW
		weights = [3]float64{shadowW, 1 - shadowW - highlightW, highlightW}
		targetL := l
		for i := range a.wheels {
			targetL += a.luminances[i] * 0.2 * weights[i]
		}
		targetL = clamp01(targetL)
		delta := (targetL - l) * 255
		rr = r + delta
		gg = g + delta
		bb = b + delta
	} else {
		// RGB -> HSL.
		h, s, l := rgbToHSL(r, g, b)

		// Насыщенность и вибрация: вибрация сильнее влияет на приглушённые цвета.
		if a.saturation != 0 || a.vibrance != 0 {
			s = clamp01(s * (1 + a.saturation + a.vibrance*(1-s)))
		}

		// Цветовой микшер: сдвиг оттенка, насыщенности и яркости по зонам.
		if a.hasMixer {
			for _, band := range a.mixer {
				w := bandWeight(h, band.center)
				if w == 0 {
					continue
				}
				h += (band.hue / 100) * 30 * w
				s = clamp01(s * (1 + (band.saturation/100)*w))
				l = clamp01(l + (band.luminance/100)*0.2*w)
			}
		}
		h = math.Mod(h, 360)
		if h < 0 {
			h += 360
		}

		// Зоны яркости: веса в сумме дают 1, баланс сдвигает границы.
		lb := clamp01(l + a.balance*0.5)
		// Более узкие зоны: колесо теней почти не задевает средние тона.
		shadowW := (1 - lb) * (1 - lb)
		shadowW *= shadowW
		highlightW := lb * lb
		highlightW *= highlightW
		weights = [3]float64{shadowW, 1 - shadowW - highlightW, highlightW}
		for i := range a.wheels {
			l = clamp01(l + a.luminances[i]*0.2*weights[i])
		}

		// HSL -> RGB.
		rr, gg, bb = hslToRGB(h, s, l)
	}

	// Точечный цвет: три колеса по зонам яркости.
	blend := a.blending
	for i, wheel := range a.wheels {
		strength := (wheel.Saturation / 100) * 0.5 * blend * weights[i]
		if strength == 0 {
			continue
		}
		tint := a.tints[i]
		rr = rr*(1-strength) + tint[0]*strength
		gg = gg*(1-strength) + tint[1]*strength
		bb = bb*(1-strength) + tint[2]*strength
	}

	// Цветокоррекция: поканальный сдвиг.
	rr *= 1 + a.correction[0]*0.5
	gg *= 1 + a.correction[1]*0.5
	bb *= 1 + a.correction[2]*0.5

	return clampFloat(rr, 0, 255), clampFloat(gg, 0, 255), clampFloat(bb, 0, 255)
}