import { Injectable, Logger } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import { Cron, CronExpression } from '@nestjs/schedule';
import { InjectRepository } from '@nestjs/typeorm';
import { Repository } from 'typeorm';
import { ImapFlow, type FetchMessageObject } from 'imapflow';
import {
  simpleParser,
  type AddressObject,
  type Attachment as MailAttachment,
} from 'mailparser';
import * as crypto from 'crypto';
import * as os from 'os';
import * as path from 'path';
import * as fs from 'fs/promises';
import { PdfService } from '../preprocessing/pdf.service';
import { EmailPageCacheService } from '../email/email-page-cache.service';
import { Email } from '../database/entities/email.entity';
import { Attachment } from '../database/entities/attachment.entity';
import { Content } from '../database/entities/content.entity';
import { isERechnung } from './zugferd.util';

@Injectable()
export class EmailDownloadService {
  private readonly logger = new Logger(EmailDownloadService.name);
  private running = false;

  constructor(
    private readonly configService: ConfigService,
    private readonly pdfService: PdfService,
    private readonly pageCache: EmailPageCacheService,
    @InjectRepository(Email) private readonly emailRepo: Repository<Email>,
    @InjectRepository(Attachment)
    private readonly attachmentRepo: Repository<Attachment>,
    @InjectRepository(Content)
    private readonly contentRepo: Repository<Content>,
  ) {}

  @Cron(CronExpression.EVERY_5_MINUTES)
  async handleCron() {
    if (this.running) {
      this.logger.warn('E-Mail-Download läuft noch – überspringe Tick.');
      return;
    }
    this.running = true;
    try {
      await this.fetchAndStore();
    } catch (err: any) {
      this.logger.error(
        `Fehler im E-Mail-Download-Job: ${err.message}`,
        err.stack,
      );
    } finally {
      this.running = false;
    }
  }

  private async fetchAndStore(): Promise<void> {
    const host = this.configService.get<string>('IMAP_HOST');
    const port = this.configService.get<number>('IMAP_PORT', 993);
    const secure =
      this.configService.get<string>('IMAP_USE_SSL', 'true') === 'true';
    const user = this.configService.get<string>('IMAP_USERNAME');
    const pass = this.configService.get<string>('IMAP_PASSWORD');

    if (!host || !user || !pass) {
      this.logger.warn(
        'IMAP-Konfiguration unvollständig – Job wird übersprungen.',
      );
      return;
    }

    this.logger.log('E-Mail Fetch Job gestartet.');

    const client = new ImapFlow({
      host,
      port,
      secure,
      auth: { user, pass },
      logger: false,
    });

    await client.connect();
    this.logger.log(`Verbunden mit IMAP-Server ${host}:${port}`);

    const lock = await client.getMailboxLock('INBOX');
    try {
      const status = await client.status('INBOX', { messages: true });
      this.logger.log(
        `Posteingang geöffnet. Anzahl der Nachrichten: ${status.messages ?? 0}`,
      );

      if (!status.messages || status.messages === 0) {
        return;
      }

      const iter = client.fetch('1:*', {
        envelope: true,
        uid: true,
        source: true,
      });

      for await (const msg of iter) {
        const messageId = msg.envelope?.messageId;
        if (!messageId) continue;

        try {
          const existing = await this.emailRepo.findOne({
            where: { MessageId: messageId },
          });
          if (existing) {
            this.logger.debug(
              `E-Mail mit MessageId ${messageId} bereits vorhanden.`,
            );
            continue;
          }

          await this.processMessage(msg);
        } catch (err: any) {
          this.logger.error(
            `Fehler beim Abrufen der Nachricht ${messageId}: ${err.message}`,
            err.stack,
          );
        }
      }

      this.logger.log(
        'Alle neuen E-Mails und deren Anhänge wurden in der Datenbank gespeichert.',
      );
    } finally {
      lock.release();
      await client.logout().catch(() => undefined);
      this.logger.log('Verbindung zum IMAP-Server geschlossen.');
    }
  }

  private async processMessage(msg: FetchMessageObject): Promise<void> {
    if (!msg.source) return;
    const parsed = await simpleParser(msg.source);
    const messageId = msg.envelope?.messageId ?? parsed.messageId ?? '';

    const email = new Email();
    email.MessageId = messageId;
    email.SenderAddress = formatAddress(parsed.from);
    email.RecipientAddress = formatAddress(parsed.to);
    email.Subject = (msg.envelope?.subject ?? parsed.subject ?? '').slice(
      0,
      500,
    );
    email.Date = msg.envelope?.date ?? parsed.date ?? new Date();
    email.Body = parsed.html || parsed.text || '';
    email.Status = 0;

    const attachmentsToPersist: Array<{
      attachment: Attachment;
      buffer: Buffer;
    }> = [];

    for (const att of parsed.attachments) {
      const entry = await this.buildAttachment(att);
      if (entry) attachmentsToPersist.push(entry);
    }

    // Double-Check: nochmal gegen DB prüfen (Race-Condition-Schutz wie in C#)
    const existing2 = await this.emailRepo.findOne({
      where: { MessageId: messageId },
    });
    if (existing2) {
      this.logger.debug(
        `E-Mail mit MessageId ${messageId} nach dem Download bereits vorhanden.`,
      );
      return;
    }

    const savedEmail = await this.emailRepo.save(email);

    for (const { attachment, buffer } of attachmentsToPersist) {
      attachment.EmailMessageId = savedEmail.Id;
      const savedAttachment = await this.attachmentRepo.save(attachment);

      const content = new Content();
      content.AttachmentEntityId = savedAttachment.Id;
      content.Content1 = buffer;
      content.ContentLength = buffer.length;
      await this.contentRepo.save(content);

      // Generate PDF thumbnails if it's a PDF
      if (savedAttachment.ContentType === 'application/pdf') {
        await this.generateThumbnailsForAttachment(savedAttachment, buffer);
      }
    }

    this.logger.debug(
      `Neue E-Mail mit MessageId ${messageId} hinzugefügt (${attachmentsToPersist.length} Anhänge).`,
    );
  }

  public async generateThumbnailsForAttachment(
    attachment: Attachment,
    buffer: Buffer,
  ): Promise<void> {
    try {
      const tempPdfPath = path.join(
        os.tmpdir(),
        `email-att-${attachment.Id}.pdf`,
      );
      await fs.writeFile(tempPdfPath, buffer);

      const images = await this.pdfService.pdfToImages(tempPdfPath, 400);
      await this.pageCache.generate(attachment.Id, images);

      attachment.PageCount = images.length;
      await this.attachmentRepo.save(attachment);

      await this.pdfService.cleanup(images);
      await fs.unlink(tempPdfPath).catch(() => {});
    } catch (err: any) {
      this.logger.warn(
        `Konnte Vorschaubilder für Anhang ${attachment.Id} nicht generieren: ${err.message}`,
      );
    }
  }

  public async backfillThumbnailsForNewEmails(): Promise<{
    processed: number;
    failed: number;
  }> {
    const emails = await this.emailRepo.find({
      where: { Status: 0 },
      relations: ['Attachments', 'Attachments.Content'],
    });

    let processed = 0;
    let failed = 0;

    for (const email of emails) {
      for (const attachment of email.Attachments) {
        if (
          attachment.ContentType === 'application/pdf' &&
          attachment.PageCount === 0 &&
          attachment.Content?.Content1
        ) {
          this.logger.log(
            `Backfill: Generiere Thumbnails für Attachment ${attachment.Id} (Email ${email.Id})`,
          );
          try {
            await this.generateThumbnailsForAttachment(
              attachment,
              attachment.Content.Content1,
            );
            processed++;
          } catch (err) {
            failed++;
          }
        }
      }
    }

    this.logger.log(
      `Backfill abgeschlossen: ${processed} erfolgreich, ${failed} fehlgeschlagen.`,
    );
    return { processed, failed };
  }

  private async buildAttachment(
    att: MailAttachment,
  ): Promise<{ attachment: Attachment; buffer: Buffer } | null> {
    const buffer = att.content;
    if (!Buffer.isBuffer(buffer) || buffer.length === 0) return null;

    const filename = att.filename ?? att.cid ?? 'unbenannt';
    let contentType = att.contentType ?? 'application/octet-stream';
    const isEmbedded = att.contentDisposition === 'inline';

    const isPdfByName = filename.toLowerCase().endsWith('.pdf');
    const isPdfByType = contentType.toLowerCase() === 'application/pdf';
    const isOctet = contentType.toLowerCase() === 'application/octet-stream';

    // Nur PDFs (inkl. als octet-stream deklarierter PDFs) und embedded rfc822 werden übernommen.
    const isRfc822 = contentType.toLowerCase() === 'message/rfc822';
    if (!isPdfByType && !isRfc822 && !(isOctet && isPdfByName)) {
      return null;
    }

    if (isPdfByName && !isPdfByType) {
      contentType = 'application/pdf';
    }

    const attachment = new Attachment();
    attachment.FileName = filename.slice(0, 255);
    attachment.ContentType = contentType.slice(0, 100);
    attachment.IsEmbedded = isEmbedded;
    attachment.ContentId = att.cid ? att.cid.slice(0, 255) : null;
    attachment.Checksum = crypto.createHash('md5').update(buffer).digest('hex');
    attachment.Erechnung =
      contentType.toLowerCase() === 'application/pdf'
        ? isERechnung(buffer)
        : false;
    attachment.ParentId = null;

    return { attachment, buffer };
  }
}

function formatAddress(
  addr: AddressObject | AddressObject[] | undefined,
): string {
  if (!addr) return '';
  const first = Array.isArray(addr) ? addr[0] : addr;
  return (first?.text ?? '').slice(0, 255);
}