<?php
/** Per-form appearance and enforced contrast rules.
 *
 * @package AccessibleForms
 */

namespace AccessibleForms;

if ( ! defined( 'ABSPATH' ) ) {
	exit();
}

class Appearance {
	/** Every surface is opaque so contrast never depends on the page behind it. */
	public static function defaults() {
		return array(
			'background'  => '#ffffff',
			'text'        => '#1d2327',
			'button'      => '#1d2327',
			'button_text' => '#ffffff',
			'border'      => '#737980',
			'font_size'   => '16',
			'spacing'     => '24',
			'radius'      => '4',
		);
	}

	public static function colors() {
		return array(
			'background'  => __( 'Form background', 'accessible-forms-by-accessible-org' ),
			'text'        => __( 'Text and focus outline', 'accessible-forms-by-accessible-org' ),
			'button'      => __( 'Button background', 'accessible-forms-by-accessible-org' ),
			'button_text' => __( 'Button text', 'accessible-forms-by-accessible-org' ),
			'border'      => __( 'Field borders', 'accessible-forms-by-accessible-org' ),
		);
	}

	public static function presets() {
		$presets = array(
			'light'  => array(
				'label'  => __( 'Classic light', 'accessible-forms-by-accessible-org' ),
				'colors' => array_intersect_key( self::defaults(), self::colors() ),
			),
			'ocean'  => array(
				'label'  => __( 'Ocean blue', 'accessible-forms-by-accessible-org' ),
				'colors' => array(
					'background'  => '#f4f8ff',
					'text'        => '#172b4d',
					'button'      => '#1856a5',
					'button_text' => '#ffffff',
					'border'      => '#687b96',
				),
			),
			'forest' => array(
				'label'  => __( 'Forest green', 'accessible-forms-by-accessible-org' ),
				'colors' => array(
					'background'  => '#f5faf6',
					'text'        => '#193c2a',
					'button'      => '#24613e',
					'button_text' => '#ffffff',
					'border'      => '#687c6e',
				),
			),
			'dark'   => array(
				'label'  => __( 'Midnight', 'accessible-forms-by-accessible-org' ),
				'colors' => array(
					'background'  => '#111827',
					'text'        => '#f9fafb',
					'button'      => '#93c5fd',
					'button_text' => '#111827',
					'border'      => '#94a3b8',
				),
			),
		);
		// Add-ons may add themes, such as saved brand presets. Every theme must pass the contrast rules.
		if ( ! function_exists( 'apply_filters' ) || ! class_exists( Extensions::class ) ) {
			return $presets;
		}
		$themes = array();
		foreach ( (array) Extensions::filter( 'accessible_forms_appearance_presets', $presets ) as $key => $theme ) {
			[$values, $errors] = self::sanitize( $theme['colors'] ?? null );
			if ( ! $errors && is_string( $theme['label'] ?? null ) ) {
				$themes[ sanitize_key( (string) $key ) ] = array(
					'label'  => $theme['label'],
					// Only what the theme sets: a colour theme must not reset text size or spacing.
					'colors' => array_intersect_key( $values, (array) $theme['colors'] ),
				);
			}
		}
		return $themes + $presets;
	}

	/** Text always meets the normal-size text threshold, regardless of font size. */
	public static function rules() {
		return array(
			array(
				'foreground' => 'text',
				'background' => 'background',
				'minimum'    => 4.5,
				'label'      => __( 'Text on form background', 'accessible-forms-by-accessible-org' ),
			),
			array(
				'foreground' => 'button_text',
				'background' => 'button',
				'minimum'    => 4.5,
				'label'      => __( 'Text on button', 'accessible-forms-by-accessible-org' ),
			),
			array(
				'foreground' => 'button',
				'background' => 'background',
				'minimum'    => 3,
				'label'      => __( 'Button against form background', 'accessible-forms-by-accessible-org' ),
			),
			array(
				'foreground' => 'border',
				'background' => 'background',
				'minimum'    => 3,
				'label'      => __( 'Field borders against form background', 'accessible-forms-by-accessible-org' ),
			),
		);
	}

	/** Relative luminance from the WCAG sRGB definition. */
	private static function luminance( $hex ) {
		$channels = array();
		foreach ( array( 1, 3, 5 ) as $offset ) {
			$value      = hexdec( substr( $hex, $offset, 2 ) ) / 255;
			$channels[] = $value <= 0.04045 ? $value / 12.92 : pow( ( $value + 0.055 ) / 1.055, 2.4 );
		}
		return 0.2126 * $channels[0] + 0.7152 * $channels[1] + 0.0722 * $channels[2];
	}

	public static function contrast( $first, $second ) {
		$a = self::luminance( $first );
		$b = self::luminance( $second );
		return ( max( $a, $b ) + 0.05 ) / ( min( $a, $b ) + 0.05 );
	}

	/** Reject invalid palettes on the server as well as in the editor. */
	public static function sanitize( $raw ) {
		$appearance = self::defaults();
		$errors     = array();
		if ( ! is_array( $raw ) ) {
			return array( $appearance, array( __( 'Choose valid form appearance settings.', 'accessible-forms-by-accessible-org' ) ) );
		}
		foreach ( self::colors() as $key => $label ) {
			$value = $raw[ $key ] ?? $appearance[ $key ];
			if ( ! is_string( $value ) || ! preg_match( '/^#[a-fA-F0-9]{6}$/D', $value ) ) {
				$errors[] = sprintf(
					/* translators: %s: color setting label. */
					__( '%s needs a six-digit hex color, such as #ffffff.', 'accessible-forms-by-accessible-org' ),
					$label
				);
			} else {
				$appearance[ $key ] = strtolower( $value );
			}
		}
		if ( ! $errors ) {
			foreach ( self::rules() as $rule ) {
				$ratio = self::contrast( $appearance[ $rule['foreground'] ], $appearance[ $rule['background'] ] );
				// Do not round before comparing: 4.499 is below 4.5.
				if ( $ratio < $rule['minimum'] ) {
					$errors[] = sprintf(
						/* translators: 1: color pair, 2: contrast ratio, 3: minimum contrast ratio. */
						__(
							'%1$s has %2$s:1 contrast; at least %3$s:1 is required. Choose a darker or lighter color.',
							'accessible-forms-by-accessible-org'
						),
						$rule['label'],
						number_format( floor( $ratio * 100 ) / 100, 2 ),
						(string) $rule['minimum']
					);
				}
			}
		}
		foreach (
			array(
				'font_size' => array( '16', '18', '20' ),
				'spacing'   => array( '16', '24', '32' ),
				'radius'    => array( '0', '4', '8', '12' ),
			)
			as $key => $allowed
		) {
			$value = $raw[ $key ] ?? $appearance[ $key ];
			if ( ! is_scalar( $value ) || ! in_array( (string) $value, $allowed, true ) ) {
				$errors[] = __(
					'Choose one of the available text sizes, field spacings, and corner styles.',
					'accessible-forms-by-accessible-org'
				);
			} else {
				$appearance[ $key ] = (string) $value;
			}
		}
		return array( $appearance, array_unique( $errors ) );
	}

	/** Older or externally changed data must not bypass the rendering safeguards. */
	public static function safe( $raw ) {
		[$appearance, $errors] = self::sanitize( $raw );
		return $errors ? self::defaults() : $appearance;
	}

	/** Values are allowlisted before being used in an escaped HTML attribute. */
	public static function css( $raw ) {
		$appearance   = self::safe( $raw );
		$declarations = array();
		foreach ( $appearance as $key => $value ) {
			$unit = isset( self::colors()[ $key ] ) ? '' : ( 'font_size' === $key ? 'rem' : 'px' );
			// Relative text sizes respect the user's browser font settings.
			if ( 'font_size' === $key ) {
				$value = (string) ( (int) $value / 16 );
			}
			$declarations[] = '--af-' . str_replace( '_', '-', $key ) . ':' . $value . $unit;
		}
		// Native date/time indicators use the browser's UI palette, not text color.
		// Derive it from the validated surface, including custom and older palettes.
		$declarations[] = '--af-color-scheme:' . (
			self::contrast( '#ffffff', $appearance['background'] ) > self::contrast( '#000000', $appearance['background'] ) ? 'dark' : 'light'
		);
		return implode( ';', $declarations );
	}
}