<?php

declare(strict_types=1);

namespace App\Config;

/**
 * YAML-backed query-enrichment configuration.
 *
 * This class intentionally has no PHP fallback values. Missing or invalid
 * configuration must be fixed in config/retriex/query_enrichment.yaml.
 */
final readonly class QueryEnricherConfig
{
    /**
     * @param array<string, mixed> $config
     */
    public function __construct(private array $config)
    {
    }

    /**
     * Returns a normalized, deduplicated mapping for the QueryEnricher.
     *
     * Output format:
     * [
     *     'term a' => 'term b',
     *     'term c' => 'term d',
     * ]
     *
     * Rules:
     * - ignore empty / invalid values
     * - trim and normalize whitespace
     * - ignore self-mappings
     * - preserve first valid rule if duplicates normalize to the same key
     *
     * @return array<string, string>
     */
    public function getEnrichQueryList(): array
    {
        $normalized = [];
        $rules = $this->requiredArray('rules');

        foreach ($rules as $key => $value) {
            if (is_array($value)) {
                $this->ingestGroup($normalized, $value);
                continue;
            }

            $left = $this->normalizePhrase(is_string($key) ? $key : '');
            $right = $this->normalizePhrase(is_string($value) ? $value : '');

            if (!$this->isValidPair($left, $right)) {
                continue;
            }

            if (!isset($normalized[$left])) {
                $normalized[$left] = $right;
            }
        }

        if ($normalized === []) {
            throw new \InvalidArgumentException('RetrieX query enrichment config key "rules" must contain at least one valid enrichment rule.');
        }

        return $normalized;
    }

    public function getMaxExpansions(): int
    {
        return $this->requiredNonNegativeInt('max_expansions');
    }

    /**
     * Returns true when at least one valid enrichment rule exists.
     */
    public function hasRules(): bool
    {
        return $this->getEnrichQueryList() !== [];
    }

    /**
     * @param array<string, string> $normalized
     * @param array<int|string, mixed> $group
     */
    private function ingestGroup(array &$normalized, array $group): void
    {
        $items = [];

        foreach ($group as $item) {
            if (!is_string($item)) {
                continue;
            }

            $item = $this->normalizePhrase($item);

            if ($item === '') {
                continue;
            }

            $items[$item] = $item;
        }

        $items = array_values($items);

        if (count($items) < 2) {
            return;
        }

        /**
         * Turn a synonym group into a conservative chain:
         * ['a', 'b', 'c'] => a=>b, b=>c
         *
         * QueryEnricher builds a bidirectional lookup later,
         * so the config output stays intentionally small.
         */
        for ($i = 0, $max = count($items) - 1; $i < $max; $i++) {
            $left = $items[$i];
            $right = $items[$i + 1];

            if (!$this->isValidPair($left, $right)) {
                continue;
            }

            if (!isset($normalized[$left])) {
                $normalized[$left] = $right;
            }
        }
    }

    private function isValidPair(string $left, string $right): bool
    {
        if ($left === '' || $right === '') {
            return false;
        }

        if ($left === $right) {
            return false;
        }

        return true;
    }

    /** @return array<int|string, mixed> */
    private function requiredArray(string $key): array
    {
        if (!array_key_exists($key, $this->config)) {
            throw new \InvalidArgumentException(sprintf('Missing required RetrieX query enrichment config key "%s".', $key));
        }

        $value = $this->config[$key];

        if (!is_array($value)) {
            throw new \InvalidArgumentException(sprintf('RetrieX query enrichment config key "%s" must be an array.', $key));
        }

        if ($value === []) {
            throw new \InvalidArgumentException(sprintf('RetrieX query enrichment config key "%s" must not be empty.', $key));
        }

        return $value;
    }

    private function requiredNonNegativeInt(string $key): int
    {
        if (!array_key_exists($key, $this->config)) {
            throw new \InvalidArgumentException(sprintf('Missing required RetrieX query enrichment config key "%s".', $key));
        }

        $value = $this->config[$key];

        if (is_int($value)) {
            $intValue = $value;
        } elseif (is_string($value) && preg_match('/^-?\d+$/', trim($value)) === 1) {
            $intValue = (int) trim($value);
        } else {
            throw new \InvalidArgumentException(sprintf('RetrieX query enrichment config key "%s" must be an integer.', $key));
        }

        if ($intValue < 0) {
            throw new \InvalidArgumentException(sprintf('RetrieX query enrichment config key "%s" must be greater than or equal to 0.', $key));
        }

        return $intValue;
    }

    private function normalizePhrase(string $value): string
    {
        $value = trim($value);

        if ($value === '') {
            return '';
        }

        $value = mb_strtolower($value, 'UTF-8');
        $value = preg_replace('/\s+/u', ' ', $value) ?? $value;

        return trim($value);
    }
}