<?php
/**
 * Rewrites attachment ids inside Gutenberg block markup.
 *
 * @package Transtrix
 */

namespace Transtrix\Reference;

defined( 'ABSPATH' ) || exit;

/**
 * Block ids live in post_content, not in meta.
 *
 * Two places carry them: the JSON attributes in the block comment, and the
 * wp-image-N class the editor writes onto the img tag. Rewriting one without
 * the other leaves an image that renders today and breaks at the next re-save.
 */
class Block_Reference_Walker {

	/**
	 * Blocks whose id attributes name attachments.
	 */
	const MEDIA_BLOCKS = array( 'image', 'cover', 'video', 'audio', 'file', 'media-text', 'gallery' );

	/**
	 * Ids the map could not translate.
	 *
	 * @var int[]
	 */
	private $unresolved = array();

	/**
	 * Rewrite every attachment id in a post's content.
	 *
	 * @param string $content The post content.
	 * @param Id_Map $map     The id map.
	 * @return array{value:string,unresolved:int[]}
	 */
	public function rewrite( string $content, Id_Map $map ): array {
		$this->unresolved = array();

		// Only inside the attributes of blocks whose ids are media. Any other
		// block's "id" is its own business, and a number that happens to be in
		// the map would be repointed at an unrelated item.
		$value = (string) preg_replace_callback(
			'#(<!--\s+wp:(?:core/)?(' . implode( '|', self::MEDIA_BLOCKS ) . ')\s+)(\{.*?\})(\s+/?-->)#s',
			function ( $block ) use ( $map ) {
				$attributes = (string) preg_replace_callback(
					'#"(id|mediaId)":(\d+)#',
					function ( $matches ) use ( $map ) {
						return '"' . $matches[1] . '":' . $this->remap( (int) $matches[2], $map );
					},
					$block[3]
				);

				$attributes = (string) preg_replace_callback(
					'#"ids":\[([\d,\s]*)\]#',
					function ( $matches ) use ( $map ) {
						$ids = array_filter( array_map( 'trim', explode( ',', $matches[1] ) ), static fn( $id ) => '' !== $id );

						return '"ids":[' . implode( ',', array_map( fn( $id ) => $this->remap( (int) $id, $map ), $ids ) ) . ']';
					},
					$attributes
				);

				return $block[1] . $attributes . $block[4];
			},
			$content
		);

		$value = (string) preg_replace_callback(
			'#wp-image-(\d+)#',
			function ( $matches ) use ( $map ) {
				return 'wp-image-' . $this->remap( (int) $matches[1], $map );
			},
			$value
		);

		return array(
			'value'      => $value,
			'unresolved' => array_values( array_unique( $this->unresolved ) ),
		);
	}

	/**
	 * Translate one id, recording it when the map has no entry.
	 *
	 * @param int    $id  Source-site id.
	 * @param Id_Map $map The id map.
	 * @return int
	 */
	private function remap( int $id, Id_Map $map ): int {
		$new = $map->get( Reference_Hint::TYPE_POST, $id );

		if ( null === $new ) {
			$this->unresolved[] = $id;
			return $id;
		}

		return $new;
	}
}