<?php
/**
 * Map the six booking-form theme knobs onto CSS the widget actually uses (docs/22 §6).
 *
 * @package Bookline
 */

declare( strict_types=1 );

namespace Bookline\Application\BookingForm;

use Bookline\Domain\BookingForm\BookingForm;

/**
 * Pure theme → CSS mapping. No WordPress APIs.
 *
 * Tailwind utilities read `--accent-500`, `--r-*` and `--font-sans`, not the
 * `--bl-*` knobs. This class resolves the knobs into those tokens so a form
 * saved in admin restyles the public widget.
 *
 * @since 0.1.0
 */
final class BookingFormThemeCss {

	/**
	 * Resolved radius lengths matching assets/tokens.css.
	 *
	 * Stored theme values are token references (`var(--r-md)`). Remapping the
	 * radius scale to `var(--bl-radius)` while `--bl-radius` is itself
	 * `var(--r-md)` is circular, so we write concrete lengths.
	 *
	 * @var array<string, string>
	 */
	private const RADIUS_PX = [
		'var(--r-sm)'   => '6px',
		'var(--r-md)'   => '10px',
		'var(--r-lg)'   => '16px',
		'var(--r-full)' => '9999px',
	];

	/**
	 * Working lime. Brand preset must not inherit admin-shell --bl-accent.
	 */
	private const BRAND_HEX = '#c4ce00';

	/**
	 * Build CSS custom properties and data attributes for a form theme.
	 *
	 * @param array<string, string> $theme Theme knobs from BookingForm::theme().
	 * @return array{properties: array<string, string>, attributes: array<string, string>}
	 */
	public static function declarations( array $theme ): array {
		$theme      = array_merge( BookingForm::default_theme(), $theme );
		$properties = [];
		$attributes = [];

		$accent = $theme['accent'];
		if ( self::is_hex( $accent ) || self::is_css_var( $accent ) ) {
			$resolved = self::resolve_accent( $accent );
		} else {
			$resolved = self::BRAND_HEX;
		}
		$properties['--bl-accent']     = $resolved;
		$properties['--accent-500']    = 'var(--bl-accent)';
		$properties['--color-primary'] = 'var(--bl-accent)';
		$properties['--accent-50']     = 'color-mix(in srgb, var(--bl-accent) 12%, var(--paper-0))';
		$properties['--accent-300']    = 'color-mix(in srgb, var(--bl-accent) 48%, var(--paper-0))';
		$properties['--accent-700']    = 'color-mix(in srgb, var(--bl-accent) 78%, var(--ink-900))';
		$properties['--on-accent']     = self::is_hex( $resolved )
			? self::on_accent_for_hex( $resolved )
			: '#0e0d0b';

		$radius = $theme['radius'];
		$properties['--bl-radius'] = isset( self::RADIUS_PX[ $radius ] )
			? self::RADIUS_PX[ $radius ]
			: '10px';

		$font = $theme['font'];
		if ( 'var(--font-mono)' === $font ) {
			$properties['--bl-font']      = 'var(--font-mono)';
			$properties['--font-sans']    = 'var(--font-mono)';
			$properties['--font-display'] = 'var(--font-mono)';
		} else {
			$properties['--bl-font'] = 'var(--font-sans)';
		}

		$density = $theme['density'];
		if ( 'compact' === $density || 'comfortable' === $density ) {
			$attributes['data-bl-density'] = $density;
		}

		$scheme = $theme['scheme'];
		if ( in_array( $scheme, [ 'light', 'dark', 'auto' ], true ) ) {
			$attributes['data-bl-scheme'] = $scheme;
			if ( 'dark' === $scheme ) {
				$attributes['data-scheme'] = 'dark';
			} elseif ( 'light' === $scheme ) {
				$attributes['data-scheme'] = 'light';
			}
		}

		$slot = $theme['slot_style'];
		if ( 'pill' === $slot || 'bordered' === $slot ) {
			$attributes['data-bl-slot-style'] = $slot;
		}

		return [
			'properties' => $properties,
			'attributes' => $attributes,
		];
	}

	/**
	 * Inline style attribute value (no wrapping quotes).
	 *
	 * @param array<string, string> $theme Theme knobs.
	 */
	public static function style_attribute( array $theme ): string {
		$properties = self::declarations( $theme )['properties'];
		$parts      = [];
		foreach ( $properties as $name => $value ) {
			$parts[] = $name . ': ' . $value;
		}
		return implode( '; ', $parts );
	}

	/**
	 * Attribute map including `style` when properties exist.
	 *
	 * @param array<string, string> $theme Theme knobs.
	 * @return array<string, string>
	 */
	public static function html_attributes( array $theme ): array {
		$declared = self::declarations( $theme );
		$out      = $declared['attributes'];
		$style    = self::style_attribute( $theme );
		if ( '' !== $style ) {
			$out['style'] = $style;
		}
		return $out;
	}

	/**
	 * Whether the value is a 3- or 6-digit hex colour.
	 *
	 * @param string $value Raw accent.
	 */
	private static function is_hex( string $value ): bool {
		return 1 === preg_match( '/^#[0-9A-Fa-f]{3}$/', $value )
			|| 1 === preg_match( '/^#[0-9A-Fa-f]{6}$/', $value );
	}

	/**
	 * Whether the value is a single CSS custom-property reference.
	 *
	 * @param string $value Raw token.
	 */
	private static function is_css_var( string $value ): bool {
		return 1 === preg_match( '/^var\(--[a-z0-9-]+\)$/', $value );
	}

	/**
	 * Map a stored accent token to a colour that does not depend on wp-admin.
	 *
	 * @param string $accent Raw accent from the form theme.
	 */
	private static function resolve_accent( string $accent ): string {
		if ( self::is_hex( $accent ) ) {
			return strtolower( $accent );
		}
		$map = [
			'var(--bl-accent)'  => self::BRAND_HEX,
			'var(--bl-brand)'   => self::BRAND_HEX,
			'var(--ink-900)'    => '#0e0d0b',
			'var(--free)'       => '#0e7c66',
			'var(--held)'       => '#b26b00',
			'var(--accent-300)' => 'color-mix(in srgb, #c4ce00 42%, #fafaf8)',
		];
		return $map[ $accent ] ?? self::BRAND_HEX;
	}

	/**
	 * Charcoal on light fills, light stone on dark fills.
	 *
	 * @param string $hex Accent including #.
	 */
	private static function on_accent_for_hex( string $hex ): string {
		return self::relative_luminance( $hex ) >= 0.45 ? '#0e0d0b' : '#f2f1ee';
	}

	/**
	 * WCAG relative luminance.
	 *
	 * @param string $hex Accent including #.
	 */
	private static function relative_luminance( string $hex ): float {
		$raw = ltrim( $hex, '#' );
		if ( 3 === strlen( $raw ) ) {
			$raw = $raw[0] . $raw[0] . $raw[1] . $raw[1] . $raw[2] . $raw[2];
		}
		if ( 6 !== strlen( $raw ) ) {
			return 1.0;
		}
		$r = self::linear_channel( (int) hexdec( substr( $raw, 0, 2 ) ) );
		$g = self::linear_channel( (int) hexdec( substr( $raw, 2, 2 ) ) );
		$b = self::linear_channel( (int) hexdec( substr( $raw, 4, 2 ) ) );
		return 0.2126 * $r + 0.7152 * $g + 0.0722 * $b;
	}

	/**
	 * Convert an sRGB channel (0–255) to linear light.
	 *
	 * @param int $channel 0–255.
	 */
	private static function linear_channel( int $channel ): float {
		$s = $channel / 255.0;
		return $s <= 0.04045 ? $s / 12.92 : pow( ( $s + 0.055 ) / 1.055, 2.4 );
	}
}