<?php

declare(strict_types=1);

namespace App\Core;

/**
 * Translation loader + t() helper.
 *
 * Loads flat `key => 'text'` arrays from `app/Locales/{locale}.php` once per
 * request per locale, caches in static memory. Supports {placeholder}
 * interpolation.
 *
 * Fallback chain: current locale → 'de' → key string itself (with optional
 * missing-key indicator in dev).
 *
 * Stateless on the instance — `t()` is a static method so views can call
 * it without a container.
 */
final class I18n
{
    /** @var array<string, array<string,string>> locale => [key => text] */
    private static array $cache = [];

    /** @var string|null Path to the Locales directory (overridable for tests) */
    private static ?string $localesPath = null;

    /**
     * Translate a key in the current locale, with {placeholder} interpolation.
     *
     * @param string               $key     Dotted key, e.g. 'nav.gallery'
     * @param array<string,string> $params  Placeholders: ['name' => 'Martin']
     * @param string|null          $locale  Override locale (defaults to current)
     */
    public static function t(string $key, array $params = [], ?string $locale = null): string
    {
        $locale ??= Locale::DEFAULT;

        // Unsupported locale = likely a developer bug; surface the key
        // rather than silently falling back to DE.
        if (!Locale::isSupported($locale)) {
            return self::interpolate($key, $params);
        }

        $text = self::lookup($key, $locale);
        if ($text === null && $locale !== Locale::DEFAULT) {
            $text = self::lookup($key, Locale::DEFAULT);
        }
        $text ??= $key;
        return self::interpolate($text, $params);
    }

    /**
     * Plural-aware translation. MVP: no ICU — we just append `{n}` to the
     * key so the caller provides singular and plural variants.
     *
     * @param array<string,string> $params
     */
    public static function tn(string $keySingular, string $keyPlural, int $n, array $params = [], ?string $locale = null): string
    {
        $key   = $n === 1 ? $keySingular : $keyPlural;
        $params = array_merge($params, ['n' => (string) $n]);
        return self::t($key, $params, $locale);
    }

    /**
     * Check whether a key exists in the given locale (or the default).
     * Useful for tests and conditional UI logic.
     */
    public static function has(string $key, ?string $locale = null): bool
    {
        $locale ??= Locale::DEFAULT;
        return self::lookup($key, $locale) !== null
            || ($locale !== Locale::DEFAULT && self::lookup($key, Locale::DEFAULT) !== null);
    }

    /**
     * Reset the in-memory cache. Test-only utility.
     */
    public static function flushCache(): void
    {
        self::$cache = [];
    }

    /**
     * Override the Locales directory. Test-only utility.
     */
    public static function setLocalesPath(string $path): void
    {
        self::$localesPath = $path;
    }

    /**
     * Look up a key in a specific locale's array.
     */
    private static function interpolate(string $text, array $params): string
    {
        if ($params === []) {
            return $text;
        }
        $search  = array_map(static fn (string $k): string => '{' . $k . '}', array_keys($params));
        $replace = array_values($params);
        return str_replace($search, $replace, $text);
    }

    private static function lookup(string $key, string $locale): ?string
    {
        if (!Locale::isSupported($locale)) {
            return null;
        }

        if (!isset(self::$cache[$locale])) {
            $file = self::localesPath() . '/' . $locale . '.php';
            if (!is_file($file)) {
                self::$cache[$locale] = [];
                return null;
            }
            $data = require $file;
            self::$cache[$locale] = is_array($data) ? $data : [];
        }

        return self::$cache[$locale][$key] ?? null;
    }

    private static function localesPath(): string
    {
        if (self::$localesPath !== null) {
            return self::$localesPath;
        }
        return dirname(__DIR__) . '/Locales';
    }
}