<?php
/**
 * Converts the template variables of another plugin into ElevenRank's.
 *
 * @package ElevenRank
 * @since   1.0.0
 */

namespace ElevenRank\Modules\Import;

defined( 'ABSPATH' ) || exit;

/**
 * A title or description template such as `%%title%% %%sep%% %%sitename%%` becomes
 * `%title% %sep% %sitename%`. A variable that ElevenRank has no equivalent for is removed from the
 * template and reported, so the site owner can see what was lost.
 *
 * @since 1.0.0
 */
final class Variable_Converter {

	/**
	 * Pattern that finds one variable. Group 1 is its name.
	 *
	 * @since 1.0.0
	 *
	 * @var string
	 */
	private $pattern;

	/**
	 * Names that map one to one: source name => ElevenRank name.
	 *
	 * @since 1.0.0
	 *
	 * @var array<string, string>
	 */
	private $names;

	/**
	 * Optional function for names that carry an argument, such as a custom field. It receives the
	 * name and returns an ElevenRank variable, or null.
	 *
	 * @since 1.0.0
	 *
	 * @var callable|null
	 */
	private $extra;

	/**
	 * Constructor.
	 *
	 * @since 1.0.0
	 *
	 * @param string                $pattern Regular expression with the variable's name in group 1.
	 * @param array<string, string> $names   Direct mappings.
	 * @param callable|null         $extra   Mapping for names that carry an argument.
	 */
	public function __construct( string $pattern, array $names, ?callable $extra = null ) {
		$this->pattern = $pattern;
		$this->names   = $names;
		$this->extra   = $extra;
	}

	/**
	 * Converts a template.
	 *
	 * @since 1.0.0
	 *
	 * @param string $template Template in the source plugin's syntax.
	 * @return array{text: string, unsupported: string[]}
	 */
	public function convert( string $template ): array {
		$unsupported = array();

		$text = (string) preg_replace_callback(
			$this->pattern,
			function ( $found ) use ( &$unsupported ) {
				$name = $found[1];

				if ( isset( $this->names[ $name ] ) ) {
					return '%' . $this->names[ $name ] . '%';
				}

				if ( null !== $this->extra ) {
					$mapped = call_user_func( $this->extra, $name );

					if ( is_string( $mapped ) && '' !== $mapped ) {
						return $mapped;
					}
				}

				$unsupported[ $name ] = $name;

				return '';
			},
			$template
		);

		$text = trim( (string) preg_replace( '/[ \t]{2,}/', ' ', $text ) );

		return array(
			'text'        => $text,
			'unsupported' => array_values( $unsupported ),
		);
	}
}