<?php
namespace StoreSuit;
defined( 'ABSPATH' ) || exit;

/**
 * What a barcode scanner meant (owner, 29 Oct 2026: "barkodu okuyucu görmüyor"). Many USB scanners are set to leave out an
 * EAN's check digit, or send a UPC with an extra 0 in front, so the number that arrives is not the one stored on the product.
 * Every lookup tries the code as it arrived first; only when no product holds it are the scanner's usual changes tried, and a
 * guess counts only when exactly one product holds what it may have meant. Two products is no answer, never a pick.
 */
final class ScanCode {
    /** The code without the spaces, line end or tab a scanner sends with it. */
    public static function clean( $code ): string {
        $code = (string) $code; $out = preg_replace( '/^[\s\x{00A0}]+|[\s\x{00A0}]+$/u', '', $code );
        return null === $out ? trim( $code ) : $out;
    }

    /** The GS1 check digit of a code's data digits (EAN-13, EAN-8, UPC-A): weights 3 and 1 from the right. */
    public static function check_digit( string $digits ): int {
        $sum = 0; $weight = 3;
        for ( $i = strlen( $digits ) - 1; $i >= 0; $i-- ) { $sum += (int) $digits[ $i ] * $weight; $weight = 4 - $weight; }
        return ( 10 - $sum % 10 ) % 10;
    }

    /**
     * The codes a scanner's usual changes stand for, without the code itself:
     * 14 digits with a 0 in front (GTIN-14): the EAN-13, and with a second 0 the UPC-A;
     * 13 digits with a 0 in front: the UPC-A it carries;
     * 12 digits: the EAN-13 without its check digit, or a UPC-A stored with a 0 in front;
     * 11 digits: a UPC-A without its check digit (as 12 digits, or as 13 with a 0 in front);
     * 7 digits: an EAN-8 without its check digit.
     * @return string[]
     */
    public static function forms( $code ): array {
        $code = self::clean( $code );
        if ( ! preg_match( '/^\d{7,14}$/D', $code ) ) { return array(); }
        $forms = array(); $len = strlen( $code );
        if ( 14 === $len && '0' === $code[0] ) { $forms[] = substr( $code, 1 ); if ( '0' === $code[1] ) { $forms[] = substr( $code, 2 ); } }
        if ( 13 === $len && '0' === $code[0] ) { $forms[] = substr( $code, 1 ); }
        if ( 12 === $len ) { $forms[] = $code . self::check_digit( $code ); $forms[] = '0' . $code; }
        if ( 11 === $len ) { $upc = $code . self::check_digit( $code ); $forms[] = $upc; $forms[] = '0' . $upc; }
        if ( 7 === $len ) { $forms[] = $code . self::check_digit( $code ); }
        return array_values( array_unique( array_diff( $forms, array( $code ) ) ) );
    }

    /**
     * The product a scanner's changed code stands for: its id and the code stored on it, or null when no product holds one of
     * the codes it may have meant, when two do, or when a product holds the code exactly as it arrived (the caller's own
     * lookup turned that one down, so no other product is offered in its place). Products and options of any status but
     * trash; every caller keeps its own rules on what may be sold, counted or bought.
     * @return array{id:int,code:string}|null
     */
    public static function match( $code ): ?array {
        $code = self::clean( $code ); $forms = self::forms( $code );
        if ( ! $forms || self::holders( array( $code ), 1 ) ) { return null; }
        $rows = self::holders( $forms, 2 );
        return 1 === count( $rows ) ? array( 'id'=>(int) key( $rows ), 'code'=>(string) current( $rows ) ) : null;
    }

    /** The id of match(), or 0. */
    public static function guess( $code ): int {
        $hit = self::match( $code );
        return $hit ? $hit['id'] : 0;
    }

    /** The code to search a list for: the code stored on the one product a scanner's changed code stands for, else the term. */
    public static function term( string $term ): string {
        $hit = self::forms( $term ) ? self::match( $term ) : null;
        return $hit ? $hit['code'] : $term;
    }

    /**
     * Up to $limit products and options holding one of these exact codes in a barcode field (WooCommerce's GTIN, _barcode,
     * _ean) or the SKU: id => the code it holds.
     * @param string[] $codes
     * @return array<int,string>
     */
    private static function holders( array $codes, int $limit ): array {
        global $wpdb;
        $codes = array_values( array_filter( array_map( 'strval', $codes ), static fn( $c ) => $c !== '' ) );
        if ( ! $codes ) { return array(); }
        $rows = $wpdb->get_results( $wpdb->prepare(
            "SELECT pm.post_id, MIN(pm.meta_value) AS code FROM %i pm JOIN %i p ON p.ID=pm.post_id WHERE pm.meta_key IN ('_global_unique_id','_barcode','_ean','_sku') AND pm.meta_value IN (" . implode( ',', array_fill( 0, count( $codes ), '%s' ) ) . ") AND p.post_type IN ('product','product_variation') AND p.post_status IN ('publish','private','draft','pending','future') GROUP BY pm.post_id LIMIT %d",
            array_merge( array( $wpdb->postmeta, $wpdb->posts ), $codes, array( $limit ) )
        ), ARRAY_A );
        $out = array();
        foreach ( (array) $rows as $row ) { $out[ (int) $row['post_id'] ] = (string) $row['code']; }
        return $out;
    }
}