<?php

declare(strict_types=1);

namespace App\Knowledge;

/**
 * KeywordSimilarity
 *
 * Deterministic and fault-tolerant comparison of two keywords.
 * Returns a similarity score between 0.0 and 1.0.
 *
 * Design goals:
 * - index.json remains unchanged
 * - comparison logic is intelligent (typos, phonetics)
 * - no alias or synonym lists
 * - no LLM dependency
 */
final class KeywordSimilarity
{
    /**
     * Compare a query token with an index keyword.
     *
     * @param string $queryToken   Token from user input
     * @param string $indexKeyword Keyword from index.json
     *
     * @return float Similarity score (0.0 – 1.0)
     */
    public static function compare(string $queryToken, string $indexKeyword): float
    {
        $a = self::normalize($queryToken);
        $b = self::normalize($indexKeyword);

        // Guard: ignore empty or very short tokens
        if ($a === '' || $b === '' || mb_strlen($a) < 3 || mb_strlen($b) < 3) {
            return 0.0;
        }

        // 1. Exact match
        if ($a === $b) {
            return 1.0;
        }

        // 2. Phonetic comparison (metaphone)
        // Useful for: showpare → shopware, shopvare → shopware
        if (metaphone($a) === metaphone($b)) {
            return 0.85;
        }

        // 3. Edit distance comparison (only for longer words)
        if (mb_strlen($a) >= 6 && mb_strlen($b) >= 6) {
            $distance = levenshtein($a, $b);

            if ($distance === 1) {
                return 0.9;
            }

            if ($distance === 2) {
                return 0.8;
            }
        }

        // No relevant match
        return 0.0;
    }

    /**
     * Normalize a keyword to ensure stable comparison.
     */
    private static function normalize(string $value): string
    {
        $value = mb_strtolower(trim($value));

        // Remove non-alphanumeric characters
        $value = preg_replace('/[^\p{L}\p{N}]/u', '', $value) ?? '';

        // Normalize German umlauts
        $map = [
            'ä' => 'ae',
            'ö' => 'oe',
            'ü' => 'ue',
            'ß' => 'ss',
        ];

        return strtr($value, $map);
    }
}