<?php

namespace App\Services\MailFlow;

use App\Jobs\SendMailMessageJob;
use App\Models\MailMessage;
use Illuminate\Support\Facades\DB;

class ImapInbox
{
    public function __construct(private AutoReplyService $replies, private IncomingContent $content) {}

    public function poll(): int
    {
        if (!function_exists('imap_open')) {
            throw new \RuntimeException('php_imap_extension_required');
        }
        $host = (string) Settings::get('imap_host');
        $folder = (string) Settings::get('imap_folder', 'INBOX');
        $port = (int) Settings::get('imap_port', 993);
        if (!preg_match('/^[a-zA-Z0-9.-]+$/', $host) || !preg_match('/^[a-zA-Z0-9_ .\/-]+$/', $folder) || $port < 1 || $port > 65535) {
            throw new \RuntimeException('imap_configuration_invalid');
        }
        foreach ([IMAP_OPENTIMEOUT, IMAP_READTIMEOUT, IMAP_WRITETIMEOUT, IMAP_CLOSETIMEOUT] as $timeout) {
            imap_timeout($timeout, 8);
        }
        // TLS with certificate validation; never accept /novalidate-cert.
        $mailbox = '{' . $host . ':' . $port . '/imap/ssl}' . $folder;
        $connection = @imap_open($mailbox, (string) Settings::get('imap_username'), (string) Settings::get('imap_password'), OP_READONLY, 1);
        if (!$connection) {
            imap_errors();
            throw new \RuntimeException('imap_connection_failed');
        }
        try {
            $status = imap_status($connection, $mailbox, SA_UIDVALIDITY | SA_UIDNEXT);
            if (!$status) {
                throw new \RuntimeException('imap_status_failed');
            }
            $identity = hash('sha256', $mailbox . ':' . Settings::get('imap_username'));
            $cursorKey = 'mail_flow_imap_' . $identity;
            $cursor = admin_setting($cursorKey);
            if (!$cursor || ($cursor['validity'] ?? null) !== $status->uidvalidity) {
                // First activation / UIDVALIDITY change: skip historical mail to avoid a reply flood.
                admin_setting([$cursorKey => ['validity' => $status->uidvalidity, 'uid' => $status->uidnext - 1]]);
                return 0;
            }
            $last = (int) $cursor['uid'];
            if ($status->uidnext <= $last + 1) {
                return 0;
            }
            // PHP's IMAP search parser does not support the UID search criterion.
            // Fetch a bounded UID range instead, without downloading message bodies.
            $upper = min($status->uidnext - 1, $last + 100);
            $overview = imap_fetch_overview($connection, ($last + 1) . ':' . $upper, FT_UID);
            if ($overview === false) {
                throw new \RuntimeException('imap_overview_failed');
            }
            $uids = array_map(static fn ($item) => (int) $item->uid, $overview);
            sort($uids, SORT_NUMERIC);
            $count = 0;
            foreach (array_slice($uids, 0, 100) as $uid) {
                if ($uid <= $last) {
                    continue;
                }
                $raw = imap_fetchheader($connection, $uid, FT_UID);
                if ($raw === false) {
                    throw new \RuntimeException('imap_header_failed');
                }
                $parsed = imap_rfc822_parse_headers($raw);
                $from = $parsed->from[0] ?? null;
                $sender = $from && isset($from->mailbox, $from->host) ? $from->mailbox . '@' . $from->host : '';
                $headers = $this->headers($raw);
                $structure = imap_fetchstructure($connection, $uid, FT_UID);
                $content = $structure ? $this->content->read($connection, $uid, $structure) : ['text' => '', 'dsn' => ''];
                $this->content->recordBounce($content['dsn'], $headers);
                $subject = isset($parsed->subject) ? mb_decode_mimeheader($parsed->subject) : '';
                $message = DB::transaction(function () use ($identity, $status, $uid, $sender, $subject, $headers, $content) {
                    $message = MailMessage::firstOrCreate(['message_key' => 'imap:' . hash('sha256', $identity . ':' . $status->uidvalidity . ':' . $uid)], [
                        'direction' => 'in', 'purpose' => 'incoming', 'channel' => 'conventional',
                        'email' => mb_substr($sender, 0, 254), 'subject' => mb_substr($subject, 0, 998),
                        'provider_id' => isset($headers['message-id']) ? mb_substr($headers['message-id'], 0, 250) : null, 'status' => 'received',
                        'payload' => ['text' => $content['text']],
                    ]);
                    $reply = $content['dsn'] === '' ? $this->replies->prepare($message, $headers) : null;
                    return $reply;
                }, 3);
                // The durable outgoing row is recoverable even if queue dispatch fails.
                if ($message) {
                    SendMailMessageJob::dispatch($message->id);
                }
                admin_setting([$cursorKey => ['validity' => $status->uidvalidity, 'uid' => $uid]]);
                $count++;
            }
            // Deleted UID gaps must not stall subsequent synchronization.
            admin_setting([$cursorKey => ['validity' => $status->uidvalidity, 'uid' => $upper]]);
            return $count;
        } finally {
            imap_close($connection);
            imap_errors();
        }
    }

    private function headers(string $raw): array
    {
        $result = [];
        $raw = preg_replace('/\r?\n[ \t]+/', ' ', $raw);
        foreach (preg_split('/\r?\n/', $raw) as $line) {
            if (str_contains($line, ':')) {
                [$key, $value] = explode(':', $line, 2);
                $result[strtolower(trim($key))] = trim($value);
            }
        }
        return $result;
    }
}