<?php

namespace Modules\Core\Auth\Services;

use Illuminate\Contracts\Auth\Authenticatable;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Auth;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\Event;
use Illuminate\Support\Facades\Mail;
use Illuminate\Support\Facades\RateLimiter;
use Modules\Core\Auth\Events\UserAuthenticated;
use Modules\Core\Auth\Events\UserCreated;
use Modules\Core\Auth\Exceptions\OtpThrottledException;
use Modules\Core\Auth\Mail\UserOtpMail;

/**
 * The storefront's passwordless login — a shopper supplies only an email
 * (Shopify-style), gets a 6-digit code, and validate() authenticates the
 * `web` guard via Auth::login().
 *
 * That alone is enough to merge/associate any active guest cart into the
 * now-known customer — Auth::login() fires Illuminate\Auth\Events\Login,
 * which Lunar's own Lunar\Listeners\CartSessionAuthListener (registered
 * unconditionally in LunarServiceProvider::boot(), no opt-in needed)
 * already listens to, calling CartSession::associate() with
 * config('lunar.cart.auth_policy') — 'merge' by default, 'override' if a
 * consumer changes that config. Deliberately no cart-association call
 * here: doing our own on top would run a SECOND merge attempt with a
 * hardcoded policy that ignores whatever the consumer configured.
 *
 * generateAndSend()'s find-or-create already triggers the full
 * Customer/User pairing cascade for a genuinely new email — see
 * Modules\Core\Auth\Events\UserCreated's own docblock and
 * Modules\Core\Customer\Listeners\CreateCustomerForUser.
 *
 * Two independent throttles, both configured under core.auth.otp — see
 * config/core.php's own comment for why they're separate: max_attempts
 * caps wrong guesses against ONE code; generation_limit caps how often a
 * NEW code can be requested for the same email at all (closes both the
 * "regenerate to reset my guess count" loophole and mail-bombing one
 * inbox).
 *
 * validate() also records a UserSessionService entry for the new login —
 * see that class's own docblock for the "logout everywhere" registry
 * this feeds (Modules\Core\Auth\Http\Middleware\EnsureSessionNotRevoked
 * is the enforcement half; a consuming app must add it to its own
 * middleware stack). $request is optional purely so this service stays
 * callable from a context with no HTTP request at all (a console
 * command, a test) — user-agent/ip are simply not recorded when omitted.
 */
class UserOtpService
{
    private const EXPIRY_MINUTES = 10;
    private const CODE_LENGTH = 6;

    public function __construct(
        private readonly UserSessionService $sessions,
    ) {}

    /**
     * @throws OtpThrottledException if this email has requested too many
     *   codes within core.auth.otp.generation_decay_minutes
     */
    public function generateAndSend(string $email): bool
    {
        $limiterKey = $this->generationLimiterKey($email);
        $maxGenerations = (int) config('core.auth.otp.generation_limit', 3);

        if (RateLimiter::tooManyAttempts($limiterKey, $maxGenerations)) {
            throw new OtpThrottledException(RateLimiter::availableIn($limiterKey));
        }

        RateLimiter::hit($limiterKey, (int) config('core.auth.otp.generation_decay_minutes', 10) * 60);

        $model = config('auth.providers.users.model');
        $user = $model::firstOrCreate(['email' => $email]);

        // wasRecentlyCreated is Eloquent's own "did firstOrCreate() just
        // INSERT, or did it find an existing row" flag — the only reliable
        // way to tell them apart from firstOrCreate()'s return value alone.
        // Without this check, a genuinely new signup never fired
        // UserCreated at all (this class's own docblock claimed the
        // Customer/User pairing cascade "already triggers" here, which was
        // false as written — see Modules\Core\Customer\Listeners\
        // CreateCustomerForUser, which depends entirely on this event).
        if ($user->wasRecentlyCreated) {
            Event::dispatch(new UserCreated($user));
        }

        $code = str_pad((string) random_int(0, 999999), self::CODE_LENGTH, '0', STR_PAD_LEFT);

        $user->otp_code = $code;
        $user->otp_expires_at = now()->addMinutes(self::EXPIRY_MINUTES);
        $user->otp_attempts = 0;
        $user->save();

        Mail::to($user->email)->send(new UserOtpMail($user->name ?? $user->email, $code));

        return true;
    }

    /**
     * A wrong code counts against core.auth.otp.max_attempts and, once
     * reached, invalidates the code entirely — the shopper must request
     * a fresh one via generateAndSend() (itself throttled independently
     * — see this class's own docblock) rather than being able to keep
     * guessing against a still-live code for the rest of its 10-minute
     * expiry window.
     */
    public function validate(string $email, string $code, ?Request $request = null): ?Authenticatable
    {
        $model = config('auth.providers.users.model');

        // lockForUpdate() + a transaction make the read-check-increment-save
        // below atomic across concurrent requests for the same user — without
        // it, two guesses fired in parallel can each read the same
        // pre-increment otp_attempts value and both save past
        // max_attempts, letting an attacker exceed the lockout by
        // parallelizing requests instead of sending them serially.
        $result = DB::transaction(function () use ($model, $email, $code) {
            $user = $model::where('email', $email)->lockForUpdate()->first();

            if (! $user || ! $user->otp_expires_at || now()->isAfter($user->otp_expires_at)) {
                return null;
            }

            if (! hash_equals((string) $user->otp_code, $code)) {
                $user->otp_attempts++;

                if ($user->otp_attempts >= (int) config('core.auth.otp.max_attempts', 5)) {
                    $user->otp_code = null;
                    $user->otp_expires_at = null;
                    $user->otp_attempts = 0;
                }

                $user->save();

                return null;
            }

            $user->otp_code = null;
            $user->otp_expires_at = null;
            $user->otp_attempts = 0;
            $user->save();

            return $user;
        });

        if (! $result) {
            return null;
        }

        RateLimiter::clear($this->generationLimiterKey($email));

        Auth::login($result);

        $this->sessions->record($result, $request);

        Event::dispatch(new UserAuthenticated($result));

        return $result;
    }

    private function generationLimiterKey(string $email): string
    {
        return 'otp-generate:'.strtolower($email);
    }
}