<?php
/**
 * Colour parsing and WCAG contrast maths.
 *
 * @package AriAccess
 */

defined( 'ABSPATH' ) || exit;

/**
 * Colour helpers.
 */
class AriAccess_Color {

	/**
	 * Palette cache: slug => hex.
	 *
	 * @var array|null
	 */
	private static $palette = null;

	/**
	 * Parse a CSS colour into [r, g, b, a] or null.
	 *
	 * @param string $value CSS colour.
	 * @return array|null
	 */
	public static function parse( $value ) {
		$value = strtolower( trim( (string) $value ) );
		$value = preg_replace( '/\s*!important$/', '', $value );
		$named = array(
			'black'  => '#000000',
			'white'  => '#ffffff',
			'red'    => '#ff0000',
			'green'  => '#008000',
			'blue'   => '#0000ff',
			'yellow' => '#ffff00',
			'gray'   => '#808080',
			'grey'   => '#808080',
			'silver' => '#c0c0c0',
			'orange' => '#ffa500',
			'navy'   => '#000080',
			'purple' => '#800080',
			'maroon' => '#800000',
			'teal'   => '#008080',
			'lime'   => '#00ff00',
			'aqua'   => '#00ffff',
			'pink'   => '#ffc0cb',
		);
		if ( isset( $named[ $value ] ) ) {
			$value = $named[ $value ];
		}
		if ( preg_match( '/^var\(--wp--preset--color--([a-z0-9-]+)\)$/', $value, $m ) ) {
			$hex = self::palette_color( $m[1] );
			return $hex ? self::parse( $hex ) : null;
		}
		if ( preg_match( '/^#([0-9a-f]{3,8})$/', $value, $m ) ) {
			$hex = $m[1];
			if ( 3 === strlen( $hex ) || 4 === strlen( $hex ) ) {
				$hex = preg_replace( '/(.)/', '$1$1', $hex );
			}
			if ( 6 !== strlen( $hex ) && 8 !== strlen( $hex ) ) {
				return null;
			}
			$a = 8 === strlen( $hex ) ? hexdec( substr( $hex, 6, 2 ) ) / 255 : 1;
			return array( hexdec( substr( $hex, 0, 2 ) ), hexdec( substr( $hex, 2, 2 ) ), hexdec( substr( $hex, 4, 2 ) ), $a );
		}
		if ( preg_match( '/^rgba?\(\s*(\d+)[\s,]+(\d+)[\s,]+(\d+)(?:[\s,\/]+([\d.]+%?))?\s*\)$/', $value, $m ) ) {
			$a = 1;
			if ( isset( $m[4] ) && '' !== $m[4] ) {
				$a = '%' === substr( $m[4], -1 ) ? (float) $m[4] / 100 : (float) $m[4];
			}
			return array( min( 255, (int) $m[1] ), min( 255, (int) $m[2] ), min( 255, (int) $m[3] ), $a );
		}
		return null;
	}

	/**
	 * Relative luminance (WCAG).
	 *
	 * @param array $rgb [r, g, b].
	 * @return float
	 */
	public static function luminance( $rgb ) {
		$c = array();
		for ( $i = 0; $i < 3; $i++ ) {
			$v     = $rgb[ $i ] / 255;
			$c[ $i ] = $v <= 0.03928 ? $v / 12.92 : pow( ( $v + 0.055 ) / 1.055, 2.4 );
		}
		return 0.2126 * $c[0] + 0.7152 * $c[1] + 0.0722 * $c[2];
	}

	/**
	 * Contrast ratio between two colours (1–21), or null if either is unknown or translucent.
	 *
	 * @param string $fg Foreground.
	 * @param string $bg Background.
	 * @return float|null
	 */
	public static function ratio( $fg, $bg ) {
		$a = is_array( $fg ) ? $fg : self::parse( $fg );
		$b = is_array( $bg ) ? $bg : self::parse( $bg );
		if ( ! $a || ! $b || $a[3] < 1 || $b[3] < 1 ) {
			return null;
		}
		$l1 = self::luminance( $a );
		$l2 = self::luminance( $b );
		return ( max( $l1, $l2 ) + 0.05 ) / ( min( $l1, $l2 ) + 0.05 );
	}

	/**
	 * Colour for a theme.json palette slug.
	 *
	 * @param string $slug Slug.
	 * @return string|null
	 */
	public static function palette_color( $slug ) {
		if ( null === self::$palette ) {
			self::$palette = array();
			if ( function_exists( 'wp_get_global_settings' ) ) {
				$palette = wp_get_global_settings( array( 'color', 'palette' ) );
				// Order matters: later origins override earlier ones.
				foreach ( array( 'default', 'theme', 'custom' ) as $origin ) {
					if ( empty( $palette[ $origin ] ) || ! is_array( $palette[ $origin ] ) ) {
						continue;
					}
					foreach ( $palette[ $origin ] as $entry ) {
						if ( isset( $entry['slug'], $entry['color'] ) ) {
							self::$palette[ $entry['slug'] ] = $entry['color'];
						}
					}
				}
			}
			/**
			 * Filter the palette used to resolve has-*-color classes.
			 *
			 * @param array $palette slug => colour.
			 */
			self::$palette = apply_filters( 'ariaccess_palette', self::$palette );
		}
		return isset( self::$palette[ $slug ] ) ? self::$palette[ $slug ] : null;
	}

	/**
	 * Reset the palette cache (tests).
	 */
	public static function reset() {
		self::$palette = null;
	}
}