<?php

namespace KTXC\L10N;

use DI\Attribute\Inject;
use KTXC\Http\Request\Request;
use KTXC\Service\UserAccountsService;

/**
 * Resolves the effective UI locale for the current user.
 *
 * Resolution chain: user setting (core.locale) -> Accept-Language
 * negotiation -> fallback. Tenant default slots in between once tenant
 * settings expose one (Phase 3).
 */
class LocaleResolver
{
    public const FALLBACK = 'en';
    public const SETTING_KEY = 'core.locale';

    public function __construct(
        private readonly UserAccountsService $userService,
        #[Inject('rootDir')] private readonly string $rootDir,
    ) {}

    /**
     * Locales with a core catalog on disk (public/l10n/*.json), always
     * including the fallback. This backs the language picker, so a locale
     * is only offered when it has at least core-shell coverage.
     *
     * @return string[]
     */
    public function available(): array
    {
        $locales = [self::FALLBACK];
        foreach (glob($this->rootDir . '/public/l10n/*.json') ?: [] as $file) {
            $locales[] = basename($file, '.json');
        }
        $locales = array_values(array_unique($locales));
        sort($locales);
        return $locales;
    }

    public function resolve(Request $request): string
    {
        $available = $this->available();

        // 1. explicit user preference
        $settings = $this->userService->fetchSettings([self::SETTING_KEY]);
        $preference = $settings[self::SETTING_KEY] ?? null;
        if (is_string($preference) && in_array($preference, $available, true)) {
            return $preference;
        }

        // 2. Accept-Language negotiation. getPreferredLanguage() returns the
        // first candidate when nothing matches, so the fallback leads the
        // list; it also normalizes to underscore form (pt_BR) while catalogs
        // use BCP-47 hyphens.
        $candidates = array_merge([self::FALLBACK], array_diff($available, [self::FALLBACK]));
        $negotiated = $request->getPreferredLanguage($candidates);
        if ($negotiated !== null) {
            $negotiated = str_replace('_', '-', $negotiated);
            if (in_array($negotiated, $available, true)) {
                return $negotiated;
            }
        }

        // 3. fallback
        return self::FALLBACK;
    }
}