<?php

declare(strict_types=1);

namespace App\Http\Middleware;

use Carbon\Carbon;
use Carbon\CarbonImmutable;
use Closure;
use Illuminate\Http\Request;
use Symfony\Component\HttpFoundation\Response;

/**
 * Resolves the locale for the request and applies it to the framework, to
 * Carbon, and to translatable model attributes.
 *
 * Precedence, most specific first:
 *
 *   1. ?lang=xx          — an explicit, single-request override (API friendly)
 *   2. session           — what the signed-in visitor picked in the switcher
 *   3. users.locale      — their stored preference
 *   4. Accept-Language   — what their client asked for
 *   5. locales.default
 */
class SetLocale
{
    public function handle(Request $request, Closure $next): Response
    {
        $locale = $this->resolve($request);

        app()->setLocale($locale);

        // Dates rendered in the panel and serialised by the API follow suit.
        CarbonImmutable::setLocale($locale);
        Carbon::setLocale($locale);

        // Translatable attributes read this locale, and fall back to
        // locales.fallback when a record has no translation for it.
        app()->setFallbackLocale((string) config('locales.fallback'));

        $response = $next($request);

        // Lets caches and clients see which language they actually received.
        $response->headers->set('Content-Language', $locale);

        return $response;
    }

    protected function resolve(Request $request): string
    {
        $supported = array_keys(config('locales.supported'));

        $candidates = [
            $request->query(config('locales.query_parameter')),
            // The API stack is stateless, so there is no session to consult.
            // hasSession() is the safe check — session() throws when unset.
            $request->hasSession()
                ? $request->session()->get(config('locales.session_key'))
                : null,
            $request->user()?->locale,
            $this->fromAcceptLanguage($request, $supported),
            config('locales.default'),
        ];

        foreach ($candidates as $candidate) {
            if (is_string($candidate) && in_array($candidate, $supported, true)) {
                return $candidate;
            }
        }

        return (string) config('locales.default');
    }

    /**
     * Pick the best supported locale from the Accept-Language header, honouring
     * its quality values. "ca-ES" matches the "ca" we support.
     *
     * @param  array<int, string>  $supported
     */
    protected function fromAcceptLanguage(Request $request, array $supported): ?string
    {
        foreach ($request->getLanguages() as $language) {
            $base = strtolower(str_replace('_', '-', $language));
            $base = explode('-', $base)[0];

            if (in_array($base, $supported, true)) {
                return $base;
            }
        }

        return null;
    }
}