<?php
/**
 * State fingerprint.
 *
 * @package Recast\WCS
 */

namespace Recast\WCS\State;

use Recast\WCS\Support\Json;

defined( 'ABSPATH' ) || exit;

/**
 * Stable hash of a state array, used to detect changes between preview and apply.
 */
final class Fingerprint {

	const VERSION = 1;

	/**
	 * Computes the fingerprint.
	 *
	 * @param array<string, mixed> $state State from StateExtractor.
	 * @return string sha256 hex.
	 */
	public static function compute( array $state ) {
		foreach ( $state as $field => $value ) {
			$state[ $field ] = self::comparable( $field, $value );
		}
		return hash( 'sha256', self::VERSION . '|' . Json::canonical( $state ) );
	}

	/**
	 * The value as fingerprints compare it. An absent custom field (null) compares equal to an
	 * empty one (''), as it did before absent fields were recorded, so stored fingerprints stay valid.
	 *
	 * @param string|int $field Field key.
	 * @param mixed      $value Value.
	 * @return mixed
	 */
	private static function comparable( $field, $value ) {
		return null === $value && 0 === strpos( (string) $field, 'meta:' ) ? '' : $value;
	}

	/**
	 * Convenience: extract then hash.
	 *
	 * @param \WC_Subscription $subscription Subscription.
	 * @param string[]         $fields       Fields.
	 * @return string
	 */
	public static function of( \WC_Subscription $subscription, array $fields ) {
		return self::compute( StateExtractor::extract( $subscription, $fields ) );
	}

	/**
	 * Fields that differ between two states.
	 *
	 * @param array<string, mixed> $before Before.
	 * @param array<string, mixed> $after  After.
	 * @return string[]
	 */
	public static function changed_fields( array $before, array $after ) {
		$changed = array();
		foreach ( array_unique( array_merge( array_keys( $before ), array_keys( $after ) ) ) as $key ) {
			$a = self::comparable( $key, array_key_exists( $key, $before ) ? $before[ $key ] : null );
			$b = self::comparable( $key, array_key_exists( $key, $after ) ? $after[ $key ] : null );
			if ( Json::canonical( $a ) !== Json::canonical( $b ) ) {
				$changed[] = $key;
			}
		}
		sort( $changed, SORT_STRING );
		return $changed;
	}

	/**
	 * Fields to fingerprint for an operation: its touched fields plus the context set.
	 *
	 * @param string[] $touched      Operation touched fields.
	 * @param string   $operation_id Operation ID.
	 * @param array    $params       Operation params.
	 * @return string[]
	 */
	public static function fields_for( array $touched, $operation_id = '', array $params = array() ) {
		$fields = array_values( array_unique( array_merge( $touched, Fields::CONTEXT ) ) );
		sort( $fields, SORT_STRING );
		/**
		 * Filters the fields fingerprinted for a run.
		 *
		 * @param string[] $fields       Fields.
		 * @param string   $operation_id Operation ID.
		 * @param array    $params       Params.
		 */
		return (array) apply_filters( 'recast_fingerprint_fields', $fields, $operation_id, $params );
	}
}