<?php
/**
 * Recursive reference rewriter.
 *
 * @package Transtrix
 */

namespace Transtrix\Reference;

defined( 'ABSPATH' ) || exit;

/**
 * Walks a meta value of any shape and rewrites the ids it contains.
 *
 * Handles scalars, arrays at any depth, serialized strings and JSON strings.
 * An id with no mapping is left exactly as it was and reported as unresolved:
 * a visible broken reference is recoverable, a silently zeroed one is not, and
 * the dry-run screen is built on that list.
 */
class Reference_Walker {

	/**
	 * Ids encountered that had no mapping, collected during a single rewrite.
	 *
	 * @var int[]
	 */
	private $unresolved = array();

	/**
	 * Rewrite every id inside a value.
	 *
	 * @param mixed          $value The meta value, any shape.
	 * @param Reference_Hint $hint  What kind of reference this key holds.
	 * @param Id_Map         $map   The id map.
	 * @return array{value:mixed,unresolved:int[]}
	 */
	public function rewrite( $value, Reference_Hint $hint, Id_Map $map ): array {
		$this->unresolved = array();

		$rewritten = $this->walk( $value, $hint, $map );

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

	/**
	 * Recursive worker.
	 *
	 * @param mixed          $value Current node.
	 * @param Reference_Hint $hint  Reference hint.
	 * @param Id_Map         $map   The id map.
	 * @return mixed
	 */
	private function walk( $value, Reference_Hint $hint, Id_Map $map ) {
		if ( is_array( $value ) ) {
			foreach ( $value as $key => $item ) {
				$value[ $key ] = $this->walk( $item, $hint, $map );
			}
			return $value;
		}

		if ( is_int( $value ) ) {
			return $this->remap( $value, $hint, $map );
		}

		if ( is_string( $value ) ) {
			return $this->walk_string( $value, $hint, $map );
		}

		// Objects, floats, booleans and null carry no ids we can safely touch.
		return $value;
	}

	/**
	 * Handle the three string shapes: serialized, JSON, plain numeric.
	 *
	 * @param string         $value Current node.
	 * @param Reference_Hint $hint  Reference hint.
	 * @param Id_Map         $map   The id map.
	 * @return string
	 */
	private function walk_string( string $value, Reference_Hint $hint, Id_Map $map ): string {
		if ( is_serialized( $value ) ) {
			$unserialized = unserialize( $value, array( 'allowed_classes' => false ) ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.serialize_unserialize -- allowed_classes is false; serialized values are rewritten in place.

			// A serialized scalar is not worth re-serializing round-trip risk for.
			if ( is_array( $unserialized ) ) {
				return maybe_serialize( $this->walk( $unserialized, $hint, $map ) );
			}

			return $value;
		}

		$first = substr( ltrim( $value ), 0, 1 );

		if ( '[' === $first || '{' === $first ) {
			$decoded = json_decode( $value, true );

			if ( is_array( $decoded ) && JSON_ERROR_NONE === json_last_error() ) {
				$encoded = wp_json_encode( $this->walk( $decoded, $hint, $map ) );

				if ( is_string( $encoded ) ) {
					return $encoded;
				}
			}

			return $value;
		}

		// A plain numeric string is an id stored as text, which is the common case.
		if ( '' !== $value && ctype_digit( $value ) ) {
			return (string) $this->remap( (int) $value, $hint, $map );
		}

		// A comma-separated list of ids, which is how more than one plugin
		// denormalises a relationship. Only ever reached under a list hint, so
		// an ordinary comma-separated string is never touched.
		if ( $hint->is_list() && 1 === preg_match( '/^\d+(,\d+)+$/', $value ) ) {
			$remapped = array();

			foreach ( explode( ',', $value ) as $id ) {
				$remapped[] = $this->remap( (int) $id, $hint, $map );
			}

			return implode( ',', $remapped );
		}

		return $value;
	}

	/**
	 * Translate one id, recording it when the map has no entry.
	 *
	 * @param int            $id   Source-site id.
	 * @param Reference_Hint $hint Reference hint.
	 * @param Id_Map         $map  The id map.
	 * @return int
	 */
	private function remap( int $id, Reference_Hint $hint, Id_Map $map ): int {
		if ( $id <= 0 ) {
			return $id;
		}

		$bucket = $hint->map_bucket();
		$new    = $map->get( $bucket, $id );

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

		return $new;
	}
}