<?php

namespace Modules\Core\Customer\Services;

use Illuminate\Contracts\Auth\Authenticatable;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\Event;
use Illuminate\Support\Facades\Hash;
use Illuminate\Support\Facades\Mail;
use Illuminate\Support\Facades\RateLimiter;
use Modules\Core\Auth\Events\UserEmailChanged;
use Modules\Core\Auth\Exceptions\OtpThrottledException;
use Modules\Core\Auth\Mail\EmailChangeCodeMail;
use Modules\Core\Auth\Mail\EmailChangedNoticeMail;
use Modules\Core\Customer\Exceptions\EmailAlreadyTakenException;
use Modules\Core\Customer\Exceptions\InvalidEmailChangeCodeException;

/**
 * Changing an account's login email — core's login is passwordless, so
 * the email IS the login, and it only ever changes once the shopper has
 * proved they can receive mail at the new address (a typo can never lock
 * them out of their own account). The pending change (new address, a
 * hash of the code, expiry, wrong-guess count) lives on the user's own
 * row (see the migration adding pending_email/pending_email_code_hash/
 * pending_email_expires_at/pending_email_attempts) — the same convention
 * Auth\Services\UserOtpService's otp_code/otp_expires_at/otp_attempts
 * already use — rather than the session, since a code arrives by email
 * and is often opened on a different device/session than the one that
 * requested it; a session-scoped pending change couldn't be confirmed
 * from there at all.
 *
 * Two independent throttles, both configured under core.auth.email_change
 * (same shape/reasoning as core.auth.otp): max_attempts caps wrong
 * guesses against ONE code; generation_limit/generation_decay_minutes cap
 * how often a NEW code can be requested at all.
 */
class CustomerEmailChangeService
{
    /**
     * @throws OtpThrottledException if this account has requested too
     *   many codes within core.auth.email_change.generation_decay_minutes
     * @throws EmailAlreadyTakenException if $newEmail already belongs to
     *   a different user
     */
    public function request(Authenticatable $user, string $newEmail): void
    {
        $newEmail = strtolower(trim($newEmail));

        if ($user->newQuery()->where('email', $newEmail)->whereKeyNot($user->getKey())->exists()) {
            throw new EmailAlreadyTakenException;
        }

        $limiterKey = $this->generationLimiterKey($user);
        $maxGenerations = (int) config('core.auth.email_change.generation_limit', 3);

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

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

        $code = str_pad((string) random_int(0, 999999), 6, '0', STR_PAD_LEFT);

        $user->forceFill([
            'pending_email' => $newEmail,
            'pending_email_code_hash' => Hash::make($code),
            'pending_email_expires_at' => now()->addMinutes((int) config('core.auth.email_change.expiry_minutes', 10)),
            'pending_email_attempts' => 0,
        ])->save();

        Mail::to($newEmail)->send(new EmailChangeCodeMail($code));
    }

    /**
     * @throws InvalidEmailChangeCodeException for a wrong, expired, or
     *   already-burned (too many wrong guesses) code, or when there is no
     *   pending change at all
     * @throws EmailAlreadyTakenException if someone else has since signed
     *   up with the pending address, in the window between request() and
     *   confirm()
     */
    public function confirm(Authenticatable $user, string $code): void
    {
        $model = $user::class;

        // lockForUpdate() + a transaction make the read-check-increment-save
        // below atomic across concurrent requests — same reasoning as
        // Auth\Services\UserOtpService::validate(), which this mirrors.
        $valid = DB::transaction(function () use ($model, $user, $code) {
            /** @var Authenticatable $locked */
            $locked = $model::whereKey($user->getKey())->lockForUpdate()->first();

            if (! $locked->pending_email
                || ! $locked->pending_email_code_hash
                || ! $locked->pending_email_expires_at
                || now()->isAfter($locked->pending_email_expires_at)) {
                return false;
            }

            if (! Hash::check($code, $locked->pending_email_code_hash)) {
                $locked->pending_email_attempts++;

                if ($locked->pending_email_attempts >= (int) config('core.auth.email_change.max_attempts', 5)) {
                    $locked->pending_email_code_hash = null;
                    $locked->pending_email_expires_at = null;
                    $locked->pending_email_attempts = 0;
                }

                $locked->save();

                return false;
            }

            return true;
        });

        if (! $valid) {
            throw new InvalidEmailChangeCodeException;
        }

        $user->refresh();
        $newEmail = $user->pending_email;

        // Someone may have signed up with this address since request() ran.
        if ($user->newQuery()->where('email', $newEmail)->whereKeyNot($user->getKey())->exists()) {
            $user->forceFill([
                'pending_email' => null,
                'pending_email_code_hash' => null,
                'pending_email_expires_at' => null,
                'pending_email_attempts' => 0,
            ])->save();

            throw new EmailAlreadyTakenException;
        }

        $oldEmail = $user->email;

        $user->forceFill([
            'email' => $newEmail,
            'email_verified_at' => now(),
            'pending_email' => null,
            'pending_email_code_hash' => null,
            'pending_email_expires_at' => null,
            'pending_email_attempts' => 0,
        ])->save();

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

        // Lets the previous owner notice if someone else changed it from a
        // hijacked session.
        Mail::to($oldEmail)->send(new EmailChangedNoticeMail($newEmail));

        // The code just proved they own the new address too.
        app(GuestOrderClaimer::class)->claim($user);

        Event::dispatch(new UserEmailChanged($user, $oldEmail));
    }

    private function generationLimiterKey(Authenticatable $user): string
    {
        return 'email-change:'.$user->getKey();
    }
}