import 'dart:math' as math;

import 'package:flutter/material.dart';

/// OkLCH color math. Lightness and chroma are perceptual here, so a palette
/// can be moved to another hue without the per-hue lightness corrections that
/// rotating an HSL hue would need.

/// Builds a color from lightness (0..1), chroma and hue (degrees). Chroma is
/// reduced until the color fits in sRGB, so a hue that can't hold the asked
/// chroma comes back muted rather than clipped to a wrong hue.
Color oklch(double lightness, double chroma, double hue) {
  var low = 0.0;
  var high = chroma;
  if (_fitsSrgb(_linearSrgb(lightness, chroma, hue))) {
    return _color(_linearSrgb(lightness, chroma, hue));
  }
  for (var i = 0; i < 16; i++) {
    final mid = (low + high) / 2;
    if (_fitsSrgb(_linearSrgb(lightness, mid, hue))) {
      low = mid;
    } else {
      high = mid;
    }
  }
  return _color(_linearSrgb(lightness, low, hue));
}

/// The WCAG contrast ratio, from 1 (identical) to 21 (black on white).
double contrastRatio(Color a, Color b) {
  final la = _relativeLuminance(a);
  final lb = _relativeLuminance(b);
  final lighter = math.max(la, lb);
  final darker = math.min(la, lb);
  return (lighter + 0.05) / (darker + 0.05);
}

/// How far a color sits from gray, in the same units [oklch] takes: the
/// bigger it is, the more vivid the color looks.
double chromaOf(Color color) {
  double linear(double value) =>
      value <= 0.04045 ? value / 12.92 : math.pow((value + 0.055) / 1.055, 2.4) as double;
  final r = linear(color.r);
  final g = linear(color.g);
  final b = linear(color.b);
  final l = math.pow(0.4122214708 * r + 0.5363325363 * g + 0.0514459929 * b, 1 / 3) as double;
  final m = math.pow(0.2119034982 * r + 0.6806995451 * g + 0.1073969566 * b, 1 / 3) as double;
  final s = math.pow(0.0883024619 * r + 0.2817188376 * g + 0.6299787005 * b, 1 / 3) as double;
  final a = 1.9779984951 * l - 2.4285922050 * m + 0.4505937099 * s;
  final bb = 0.0259040371 * l + 0.7827717662 * m - 0.8086757660 * s;
  return math.sqrt(a * a + bb * bb);
}

List<double> _linearSrgb(double lightness, double chroma, double hue) {
  final radians = hue * math.pi / 180;
  final a = chroma * math.cos(radians);
  final b = chroma * math.sin(radians);
  final l = math.pow(lightness + 0.3963377774 * a + 0.2158037573 * b, 3) as double;
  final m = math.pow(lightness - 0.1055613458 * a - 0.0638541728 * b, 3) as double;
  final s = math.pow(lightness - 0.0894841775 * a - 1.2914855480 * b, 3) as double;
  return [
    4.0767416621 * l - 3.3077115913 * m + 0.2309699292 * s,
    -1.2684380046 * l + 2.6097574011 * m - 0.3413193965 * s,
    -0.0041960863 * l - 0.7034186147 * m + 1.7076147010 * s,
  ];
}

bool _fitsSrgb(List<double> rgb) =>
    rgb.every((channel) => channel >= -0.0001 && channel <= 1.0001);

Color _color(List<double> rgb) => Color.fromARGB(
      255,
      _encode(rgb[0]),
      _encode(rgb[1]),
      _encode(rgb[2]),
    );

int _encode(double channel) {
  final clamped = channel.clamp(0.0, 1.0);
  final encoded = clamped <= 0.0031308
      ? 12.92 * clamped
      : 1.055 * math.pow(clamped, 1 / 2.4) - 0.055;
  return (encoded * 255).round().clamp(0, 255);
}

double _relativeLuminance(Color color) {
  double channel(double value) =>
      value <= 0.04045 ? value / 12.92 : math.pow((value + 0.055) / 1.055, 2.4) as double;
  return 0.2126 * channel(color.r) + 0.7152 * channel(color.g) + 0.0722 * channel(color.b);
}