<?php
/**
 * Colours of the chrome: validation, the default palette of the sections, the ink (the text-safe shade) and the text
 * colour on a fill, and the inline CSS that gives every product and section its custom properties (printed with
 * wp_add_inline_style(), so the markup carries no style attribute and passes wp_kses()).
 *
 * @package RoosterAdmin
 */

namespace Rooster\Admin;

defined( 'ABSPATH' ) || exit;

/**
 * Static.
 */
final class Colour {

	/**
	 * The default section fills, in order (Rooster LMS's six, then two more), when a product names none.
	 */
	private const PALETTE = array( '#75beff', '#ff8080', '#8fe03a', '#ffde00', '#b794f6', '#a1a1aa', '#5eead4', '#fdba74' );

	/**
	 * A 6-digit hex colour from a value, or the fallback.
	 *
	 * @param string $value    Value ('#abc' or '#aabbcc').
	 * @param string $fallback Fallback.
	 */
	public static function hex( string $value, string $fallback ): string {
		$value = strtolower( trim( $value ) );
		if ( 1 === preg_match( '/^#[0-9a-f]{6}$/', $value ) ) {
			return $value;
		}
		if ( 1 === preg_match( '/^#([0-9a-f])([0-9a-f])([0-9a-f])$/', $value, $m ) ) {
			return '#' . $m[1] . $m[1] . $m[2] . $m[2] . $m[3] . $m[3];
		}
		return $fallback;
	}

	/**
	 * The default fill of the n-th section.
	 *
	 * @param int $n Index.
	 */
	public static function palette( int $n ): string {
		return self::PALETTE[ $n % count( self::PALETTE ) ];
	}

	/**
	 * The RGB components of a hex colour.
	 *
	 * @param string $hex 6-digit hex colour.
	 * @return array{0: int, 1: int, 2: int}
	 */
	public static function rgb( string $hex ): array {
		$hex = ltrim( $hex, '#' );
		return array( (int) hexdec( substr( $hex, 0, 2 ) ), (int) hexdec( substr( $hex, 2, 2 ) ), (int) hexdec( substr( $hex, 4, 2 ) ) );
	}

	/**
	 * The relative luminance (WCAG) of a hex colour.
	 *
	 * @param string $hex 6-digit hex colour.
	 */
	public static function luminance( string $hex ): float {
		$out = array();
		foreach ( self::rgb( $hex ) as $c ) {
			$c     = $c / 255;
			$out[] = $c <= 0.03928 ? $c / 12.92 : ( ( $c + 0.055 ) / 1.055 ) ** 2.4;
		}
		return 0.2126 * $out[0] + 0.7152 * $out[1] + 0.0722 * $out[2];
	}

	/**
	 * The contrast ratio of two hex colours.
	 *
	 * @param string $a Colour.
	 * @param string $b Colour.
	 */
	public static function contrast( string $a, string $b ): float {
		$la = self::luminance( $a );
		$lb = self::luminance( $b );
		return ( max( $la, $lb ) + 0.05 ) / ( min( $la, $lb ) + 0.05 );
	}

	/**
	 * A hex colour mixed with black (amount 0..1 of black).
	 *
	 * @param string $hex    Colour.
	 * @param float  $amount Share of black.
	 */
	public static function darken( string $hex, float $amount ): string {
		$out = '#';
		foreach ( self::rgb( $hex ) as $c ) {
			$out .= str_pad( dechex( (int) round( $c * ( 1 - $amount ) ) ), 2, '0', STR_PAD_LEFT );
		}
		return $out;
	}

	/**
	 * The ink of a fill: the fill darkened until white text reads on it at 4.5:1 (the current pill, the links and the
	 * headings in the section's colour). A warm fill (orange to yellow) mixed with black turns brown or olive, so its
	 * ink turns towards red-orange and keeps its saturation as it darkens (0.46.8; the owner: never brown). A red keeps
	 * its hue and saturation the same way (0.68.4; the owner: mixed with black, the LMS's red was "a brick tile of 300
	 * years", washed out).
	 *
	 * @param string $hex Fill.
	 */
	public static function ink( string $hex ): string {
		if ( self::contrast( $hex, '#ffffff' ) >= 4.5 ) {
			return $hex;
		}
		[ $h, $s, $l ] = self::hsl( $hex );
		$red           = $h < 18.0 || $h >= 345.0;
		if ( $s >= 0.15 && ( $red || $h <= 70.0 ) ) {
			if ( ! $red ) {
				$h = 17.0 + ( $h - 17.0 ) * 0.2;
			}
			$s = max( $s, 0.85 );
			for ( $i = 0; $i < 80 && self::contrast( self::from_hsl( $h, $s, $l ), '#ffffff' ) < 4.5; $i++ ) {
				$l -= 0.01;
			}
			return self::from_hsl( $h, $s, $l );
		}
		$ink = $hex;
		for ( $i = 0; $i < 12 && self::contrast( $ink, '#ffffff' ) < 4.5; $i++ ) {
			$ink = self::darken( $ink, 0.12 );
		}
		return $ink;
	}

	/**
	 * A hex colour as hue (degrees), saturation and lightness (0..1).
	 *
	 * @param string $hex Colour.
	 * @return array{0: float, 1: float, 2: float}
	 */
	public static function hsl( string $hex ): array {
		[ $r, $g, $b ] = array_map( static fn( int $c ): float => $c / 255, self::rgb( $hex ) );
		$max           = max( $r, $g, $b );
		$min           = min( $r, $g, $b );
		$l             = ( $max + $min ) / 2;
		$d             = $max - $min;
		if ( $d <= 0.0 ) {
			return array( 0.0, 0.0, $l );
		}
		$s = $d / ( 1 - abs( 2 * $l - 1 ) );
		if ( $max === $r ) {
			$h = 60 * fmod( ( $g - $b ) / $d + 6, 6 );
		} elseif ( $max === $g ) {
			$h = 60 * ( ( $b - $r ) / $d + 2 );
		} else {
			$h = 60 * ( ( $r - $g ) / $d + 4 );
		}
		return array( $h, $s, $l );
	}

	/**
	 * Hue (degrees), saturation and lightness (0..1) as a hex colour.
	 *
	 * @param float $h Hue.
	 * @param float $s Saturation.
	 * @param float $l Lightness.
	 */
	public static function from_hsl( float $h, float $s, float $l ): string {
		$l = max( 0.0, min( 1.0, $l ) );
		$c = ( 1 - abs( 2 * $l - 1 ) ) * max( 0.0, min( 1.0, $s ) );
		$x = $c * ( 1 - abs( fmod( $h / 60, 2 ) - 1 ) );
		$m = $l - $c / 2;
		$k = (int) floor( fmod( $h, 360 ) / 60 );
		$p = array( array( $c, $x, 0 ), array( $x, $c, 0 ), array( 0, $c, $x ), array( 0, $x, $c ), array( $x, 0, $c ), array( $c, 0, $x ) )[ max( 0, min( 5, $k ) ) ];
		$out = '#';
		foreach ( $p as $v ) {
			$out .= str_pad( dechex( (int) round( ( $v + $m ) * 255 ) ), 2, '0', STR_PAD_LEFT );
		}
		return $out;
	}

	/**
	 * The ink of a fill on the dark scheme (0.24.0): the fill lifted until it reads on the dark background (#09090b)
	 * at 4.5:1; Colour::css() prints it as the dark half of each ink's light-dark() pair.
	 *
	 * @param string $hex Fill.
	 */
	public static function ink_dark( string $hex ): string {
		$ink = $hex;
		for ( $i = 0; $i < 12 && self::contrast( $ink, '#09090b' ) < 4.5; $i++ ) {
			$ink = self::tint( $ink, 0.12 );
		}
		return $ink;
	}

	/**
	 * A colour lifted until it reads on the dark admin menu (3.2:1 against #1d2327, the default scheme's panel):
	 * the product's colour as the side menu shows it (the wordmark's last letters, 0.17.5). A colour that reads
	 * already comes back as it is.
	 *
	 * @param string $hex Colour.
	 */
	public static function lift( string $hex ): string {
		$out = strtolower( $hex );
		for ( $i = 0; $i < 12 && self::contrast( $out, '#1d2327' ) < 3.2; $i++ ) {
			$parts = array();
			foreach ( self::rgb( $out ) as $c ) {
				$parts[] = str_pad( dechex( (int) round( $c + ( 255 - $c ) * 0.14 ) ), 2, '0', STR_PAD_LEFT );
			}
			$out = '#' . implode( '', $parts );
		}
		return $out;
	}

	/**
	 * A colour moved towards another (amount 0..1 of the other): the start of a word's gradient, which carries the
	 * red of the letter before it.
	 *
	 * @param string $hex    Colour.
	 * @param string $other  The other colour.
	 * @param float  $amount Share of the other.
	 */
	public static function mix( string $hex, string $other, float $amount ): string {
		$out = '#';
		$b   = self::rgb( $other );
		foreach ( self::rgb( $hex ) as $i => $c ) {
			$out .= str_pad( dechex( (int) round( $c + ( $b[ $i ] - $c ) * $amount ) ), 2, '0', STR_PAD_LEFT );
		}
		return $out;
	}

	/**
	 * A colour mixed with white (amount 0..1 of white): the lighter end of a word's gradient.
	 *
	 * @param string $hex    Colour.
	 * @param float  $amount Share of white.
	 */
	public static function tint( string $hex, float $amount ): string {
		$out = '#';
		foreach ( self::rgb( $hex ) as $c ) {
			$out .= str_pad( dechex( (int) round( $c + ( 255 - $c ) * $amount ) ), 2, '0', STR_PAD_LEFT );
		}
		return $out;
	}

	/**
	 * Black or white, whichever reads better on a fill.
	 *
	 * @param string $hex Fill.
	 */
	public static function on( string $hex ): string {
		return self::contrast( $hex, '#09090b' ) >= self::contrast( $hex, '#ffffff' ) ? '#09090b' : '#ffffff';
	}

	/**
	 * Whether a colour is warm (0.58.0, UI-Final-Review FR10): a red or an orange, hue under 45 or over 330 degrees,
	 * saturated at least 15 %. On a warm section a warning or a destructive tone would no longer stand out, so its
	 * colour stays on the 3 px accent, the icon and the focus ring and never washes a head (wash()).
	 *
	 * @param string $hex 6-digit hex colour.
	 */
	public static function is_warm( string $hex ): bool {
		[ $h, $s ] = self::hsl( $hex );
		return $s >= 0.15 && ( $h < 45.0 || $h > 330.0 );
	}

	/**
	 * The wash of a card head in a colour (0.58.0): 7 % of the colour on the background, or the background itself for
	 * a warm colour (FR10). A CSS value, right in both schemes (the background is a light-dark() token).
	 *
	 * @param string $hex 6-digit hex colour.
	 */
	public static function wash( string $hex ): string {
		return self::is_warm( $hex ) ? 'var(--ra-background)' : 'color-mix(in srgb,' . $hex . ' 7%,var(--ra-background))';
	}

	/**
	 * The ink of a fill and the text colour on it, each a light-dark() pair: the light ink reads on white, the dark
	 * ink on the dark background (0.24.0).
	 *
	 * @param string $hex Fill.
	 * @return array{0: string, 1: string} The ink pair and the on pair, as CSS values.
	 */
	public static function inks( string $hex ): array {
		$light = self::ink( $hex );
		$dark  = self::ink_dark( $hex );
		return array( 'light-dark(' . $light . ',' . $dark . ')', 'light-dark(' . self::on( $light ) . ',' . self::on( $dark ) . ')' );
	}

	/**
	 * The screen's section on the body (0.25.0): `--ra-screen-sec`, `--ra-screen-sec-ink` and `--ra-screen-sec-on`,
	 * for what sits outside a section's own element (a product's content panel, a dropdown a script appends to
	 * <body>); '' on Home or on a screen without a section. The section's own variables (`--ra-sec*`) stay on the
	 * elements that carry the section class, so a card or a pill of another section keeps its colour. Since 0.58.0
	 * `--ra-screen-wash`, the wash of a head outside a section's element: the screen's section's, else the product's.
	 *
	 * @param Registry             $registry The registry.
	 * @param array<string, mixed> $product  The current product.
	 */
	private static function screen_section( Registry $registry, array $product ): string {
		$slug    = (string) $product['slug'];
		$section = $registry->current_section( $slug, $registry->visible( $slug ) );
		if ( '' === $section || ! isset( $product['sections'][ $section ] ) ) {
			return ';--ra-screen-wash:' . self::wash( (string) $product['colour'] );
		}
		$colour = (string) $product['sections'][ $section ]['colour'];
		$pair   = self::inks( $colour );
		return ';--ra-screen-sec:' . $colour . ';--ra-screen-sec-ink:' . $pair[0] . ';--ra-screen-sec-on:' . $pair[1] . ';--ra-screen-wash:' . self::wash( $colour );
	}

	/**
	 * The inline CSS of every registered product and its sections and audiences: the custom properties the
	 * stylesheet reads (--ra-product, --ra-sec, --ra-sec-ink, --ra-sec-on, --ra-persona).
	 *
	 * @param Registry $registry The registry.
	 */
	public static function css( Registry $registry ): string {
		$css     = '';
		$current = $registry->current_product();
		foreach ( $registry->products() as $slug => $product ) {
			$class = '.rooster-admin-product-' . $slug;
			$word  = array() !== $product['word']['gradient'] ? ';--ra-word-from:' . $product['word']['gradient'][0] . ';--ra-word-to:' . $product['word']['gradient'][1] : '';
			$pair  = self::inks( $product['colour'] ); // the on-colour against the ink, which is what the fills use (0.22.0); both schemes (0.24.0)
			$css  .= $class . '{--ra-product:' . $product['colour'] . ';--ra-product-ink:' . $pair[0] . ';--ra-product-on:' . $pair[1] . $word . '}';
			if ( $slug === $current ) {
				$css .= '.rooster-admin-has-chrome{--ra-product:' . $product['colour'] . ';--ra-product-ink:' . $pair[0] . ';--ra-product-on:' . $pair[1] . $word . ( '' !== $product['hero_image'] ? ';--ra-hero:url(' . esc_url( $product['hero_image'] ) . ')' : '' ) . self::screen_section( $registry, $product ) . '}';
			}
			foreach ( $product['sections'] as $key => $section ) {
				$sec  = self::inks( $section['colour'] );
				$css .= '.rooster-admin-sec-' . $slug . '--' . $key . '{--ra-sec:' . $section['colour'] . ';--ra-sec-ink:' . $sec[0] . ';--ra-sec-on:' . $sec[1] . ';--ra-sec-wash:' . self::wash( $section['colour'] ) . ';--ra-accent:' . $sec[0] . ';--ra-accent-on:' . $sec[1] . ';--ra-shadow-focus:0 0 0 1px ' . $sec[0] . '}'; // the accent of the controls inside (0.45.0); the head's wash, none on a warm section (0.58.0)
			}
			foreach ( $product['audiences'] as $key => $persona ) {
				$css .= '.rooster-admin-persona-' . $slug . '--' . $key . '{--ra-persona:' . $persona['colour'] . '}';
			}
		}
		return $css;
	}
}