index/src/Colour/Colour.php

<?php
namespace Index\Colour;

use Stringable;

abstract class Colour implements Stringable {
    public abstract function getRed(): int;
    public abstract function getGreen(): int;
    public abstract function getBlue(): int;
    public abstract function getAlpha(): float;

    public abstract function shouldInherit(): bool;

    public abstract function __toString(): string;

    private const READABILITY_THRESHOLD = 186;
    private const LUMINANCE_WEIGHT_RED = .299;
    private const LUMINANCE_WEIGHT_GREEN = .587;
    private const LUMINANCE_WEIGHT_BLUE = .114;

    public function getLuminance(): float {
        return self::LUMINANCE_WEIGHT_RED   * $this->getRed()
             + self::LUMINANCE_WEIGHT_GREEN * $this->getGreen()
             + self::LUMINANCE_WEIGHT_BLUE  * $this->getBlue();
    }

    public function isBright(): bool {
        return $this->getLuminance() > self::READABILITY_THRESHOLD;
    }

    public function isDark(): bool {
        return $this->getLuminance() <= self::READABILITY_THRESHOLD;
    }

    private static ColourNull $none;

    public static function none(): Colour {
        return self::$none;
    }

    private const MSZ_INHERIT = 0x40000000;

    public static function fromMisuzu(int $raw): Colour {
        if($raw & self::MSZ_INHERIT)
            return self::$none;
        return ColourRGB::fromRawRGB($raw);
    }

    public static function parse(?string $value): Colour {
        if($value === null)
            return self::$none;

        $value = strtolower(trim($value));
        if($value === '' || $value === 'inherit')
            return self::$none;

        if(ctype_alpha($value))
            return new ColourNamed($value);

        if($value[0] === '#') {
            $value = substr($value, 1);

            if(ctype_xdigit($value)) {
                $length = strlen($value);

                if($length === 3) {
                    $value = $value[0] . $value[0] . $value[1] . $value[1] . $value[2] . $value[2];
                    $length *= 2;
                } elseif($length === 4) {
                    $value = $value[0] . $value[0] . $value[1] . $value[1] . $value[2] . $value[2] . $value[3] . $value[3];
                    $length *= 2;
                }

                if($length === 6)
                    return ColourRGB::fromRawRGB(hexdec($value));
                if($length === 8)
                    return ColourRGB::fromRawRGBA(hexdec($value));
            }

            return self::$none;
        }

        if(str_starts_with($value, 'rgb(') || str_starts_with($value, 'rgba(')) {
            $open = strpos($value, '(');
            if($open === false)
                return self::$none;

            $close = strpos($value, ')', $open);
            if($close === false)
                return self::$none;

            $open += 1;
            $value = substr($value, $open, $close - $open);

            if(strpos($value, ',') === false) {
                // todo: support comma-less syntax
                return self::$none;
            } else {
                $value = explode(',', $value, 4);
                $parts = count($value);
                if($parts !== 3 && $parts !== 4)
                    return self::$none;

                $value[0] = (int)trim($value[0]);
                $value[1] = (int)trim($value[1]);
                $value[2] = (int)trim($value[2]);
                $value[3] = (float)trim($value[3] ?? '1');
            }

            return new ColourRGB(...$value);
        }

        if(str_starts_with($value, 'hsl(') || str_starts_with($value, 'hsla(')) {
            $open = strpos($value, '(');
            if($open === false)
                return self::$none;

            $close = strpos($value, ')', $open);
            if($close === false)
                return self::$none;

            $open += 1;
            $value = substr($value, $open, $close - $open);

            if(strpos($value, ',') === false) {
                // todo: support comma-less syntax
                return self::$none;
            } else {
                $value = explode(',', $value, 4);
                $parts = count($value);
                if($parts !== 3 && $parts !== 4)
                    return self::$none;

                if(!str_ends_with($value[1], '%') || !str_ends_with($value[2], '%'))
                    return self::$none;

                $value[1] = (float)substr($value[1], 0, -1);
                $value[2] = (float)substr($value[2], 0, -1);

                if($value[1] < 0 || $value[1] > 100 || $value[2] < 0 || $value[2] > 100)
                    return self::$none;

                $value[1] /= 100.0;
                $value[2] /= 100.0;

                if(ctype_digit($value[0])) {
                    $value[0] = (float)$value[0];
                } else {
                    if(str_ends_with($value[0], 'deg')) {
                        $value[0] = (float)substr($value[0], 0, -3);
                    } elseif(str_ends_with($value[0], 'grad')) {
                        $value[0] = 0.9 * (float)substr($value[0], 0, -4);
                    } elseif(str_ends_with($value[0], 'rad')) {
                        $value[0] = rad2deg((float)substr($value[0], 0, -3));
                    } elseif(str_ends_with($value[0], 'turn')) {
                        $value[0] = 360.0 * ((float)substr($value[0], 0, -4));
                    } else {
                        return self::$none;
                    }
                }

                $value[3] = (float)trim($value[3] ?? '1');
            }

            return new ColourHSL(...$value);
        }

        return self::$none;
    }

    public static function init(): void {
        self::$none = new ColourNull;
    }
}

Colour::init();