import { Injectable, Logger, OnModuleInit, OnModuleDestroy } from '@nestjs/common';
import { Cron } from '@nestjs/schedule';
import { ConfigService } from '@nestjs/config';
import { InjectRepository } from '@nestjs/typeorm';
import { IsNull, Repository } from 'typeorm';
import { randomUUID } from 'crypto';
import * as chokidar from 'chokidar';
import * as path from 'path';
import * as fs from 'fs/promises';
import { BarcodeScannerService } from '../barcode/barcode-scanner.service';
import { PageCacheService } from '../barcode/page-cache.service';
import {
  InboxDocument,
  type InboxSource,
} from '../database/entities/inbox-document.entity';

const STABILITY_MS = 5000;

@Injectable()
export class ScannerWatcherService implements OnModuleInit, OnModuleDestroy {
  private readonly logger = new Logger(ScannerWatcherService.name);
  private watcher: chokidar.FSWatcher | null = null;
  private readonly sourceRoot: string;
  private readonly processing = new Set<string>();
  private isPeriodicScanning = false;

  constructor(
    private readonly configService: ConfigService,
    private readonly barcodeScanner: BarcodeScannerService,
    private readonly pageCache: PageCacheService,
    @InjectRepository(InboxDocument)
    private readonly documentRepo: Repository<InboxDocument>,
  ) {
    this.sourceRoot = this.configService.get<string>('SCANNER_WATCH_DIR', '/mnt/scans');
  }

  onModuleInit(): void {
    this.startWatching();
    // Sequenziell, sonst greifen sich initialScan (Watcher) und Backfill
    // dieselbe frisch angelegte Row und scannen doppelt. Fire-and-forget,
    // damit der Modulstart nicht blockiert.
    void this.bootstrap();
  }

  private async bootstrap(): Promise<void> {
    await this.initialScan();
    await this.backfillMissingScans();
  }

  onModuleDestroy(): void {
    this.stopWatching();
  }

  private startWatching(): void {
    this.logger.log(`Starte Überwachung: ${this.sourceRoot}`);

    this.watcher = chokidar.watch(this.sourceRoot, {
      ignored: /(^|[\/\\])\../,
      persistent: true,
      ignoreInitial: true,
      awaitWriteFinish: {
        stabilityThreshold: STABILITY_MS,
        pollInterval: 500,
      },
      depth: 1,
    });

    this.watcher
      .on('add', (filePath: string) => this.handleNewFile(filePath))
      .on('error', (error: Error) => this.logger.error(`Watcher Fehler: ${error.message}`));

    this.logger.log('Scanner-Watcher aktiv');
  }

  private stopWatching(): void {
    if (this.watcher) {
      this.watcher.close();
      this.logger.log('Scanner-Watcher gestoppt');
    }
  }

  private async initialScan(silent = false): Promise<void> {
    let subdirs: string[];
    try {
      const entries = await fs.readdir(this.sourceRoot, { withFileTypes: true });
      subdirs = entries.filter((e) => e.isDirectory()).map((e) => e.name);
    } catch (err: any) {
      if (!silent) {
        this.logger.warn(`Scanner-Check: Quellverzeichnis nicht lesbar (${this.sourceRoot}): ${err.message}`);
      }
      return;
    }

    let seen = 0;
    for (const subdir of subdirs) {
      const dir = path.join(this.sourceRoot, subdir);
      let files: string[];
      try {
        files = await fs.readdir(dir);
      } catch (err: any) {
        if (!silent) {
          this.logger.warn(`Scanner-Check: ${dir} nicht lesbar: ${err.message}`);
        }
        continue;
      }

      for (const name of files) {
        if (path.extname(name).toLowerCase() !== '.pdf') continue;
        const full = path.join(dir, name);

        if (!(await this.isStable(full))) {
          if (!silent) {
            this.logger.debug(`Scanner-Check: ${full} noch nicht stabil – Watcher übernimmt`);
          }
          continue;
        }

        seen += 1;
        await this.handleNewFile(full);
      }
    }

    if (seen > 0) {
      this.logger.log(`Scanner-Check: ${seen} Datei(en) verarbeitet`);
    } else if (!silent) {
      this.logger.log('Scanner-Check: keine neuen Dateien gefunden');
    }
  }

  @Cron('*/15 * * * * *')
  async periodicScan(): Promise<void> {
    if (this.isPeriodicScanning) return;
    this.isPeriodicScanning = true;
    try {
      await this.initialScan(true);
    } catch (err: any) {
      this.logger.error(`Periodic Scan Fehler: ${err.message}`);
    } finally {
      this.isPeriodicScanning = false;
    }
  }

  private async isStable(filePath: string): Promise<boolean> {
    try {
      const stat = await fs.stat(filePath);
      return Date.now() - stat.mtimeMs >= STABILITY_MS;
    } catch {
      return false;
    }
  }

  private async handleNewFile(filePath: string): Promise<void> {
    if (path.extname(filePath).toLowerCase() !== '.pdf') return;

    const relative = path.relative(this.sourceRoot, filePath);
    const parts = relative.split(path.sep);

    if (parts.length !== 2) {
      this.logger.debug(`Überspringe (falsche Tiefe): ${filePath}`);
      return;
    }

    const subdir = parts[0];
    const fileName = parts[1];

    if (this.processing.has(filePath)) return;
    this.processing.add(filePath);

    try {
      const id = randomUUID();
      const source: InboxSource = subdir === 'all' ? 'all' : 'user';
      const owner = source === 'all' ? null : subdir;

      const targetDir = this.pageCache.documentDir(id);
      const targetPdf = this.pageCache.documentPdfPath(id);
      await fs.mkdir(targetDir, { recursive: true });

      await this.move(filePath, targetPdf);

      const doc = this.documentRepo.create({
        Id: id,
        OriginalName: fileName,
        Source: source,
        OwnerUsername: owner,
        PageCount: 0,
        QrCodes: [],
      });
      await this.documentRepo.save(doc);

      this.logger.log(`Übernommen: ${relative} → ${id}/document.pdf`);

      try {
        await this.barcodeScanner.scanAndMatch(doc);
      } catch (err: any) {
        this.logger.warn(`Barcode-Scan nach Move fehlgeschlagen (${id}): ${err.message}`);
      }
    } catch (err: any) {
      this.logger.error(`Übernahme fehlgeschlagen für ${filePath}: ${err.message}`);
    } finally {
      this.processing.delete(filePath);
    }
  }

  private async backfillMissingScans(): Promise<void> {
    let pending: InboxDocument[];
    try {
      pending = await this.documentRepo.find({
        where: [{ PageCount: 0 }, { QrCodes: IsNull() }],
      });
    } catch (err: any) {
      this.logger.warn(`Backfill: DB-Query fehlgeschlagen: ${err.message}`);
      return;
    }

    let scanned = 0;
    for (const doc of pending) {
      try {
        const didScan = await this.barcodeScanner.ensureScanned(doc);
        if (didScan) scanned += 1;
      } catch (err: any) {
        this.logger.warn(`Backfill fehlgeschlagen (${doc.Id}): ${err.message}`);
      }
    }

    if (scanned > 0) {
      this.logger.log(`Backfill: ${scanned} Datei(en) nachträglich gescannt`);
    } else {
      this.logger.log('Backfill: alle Dateien bereits gescannt');
    }
  }

  private async move(src: string, dest: string): Promise<void> {
    try {
      await fs.rename(src, dest);
      return;
    } catch (err: any) {
      if (err.code !== 'EXDEV') throw err;
    }
    // Cross-device: copy + unlink. Wenn unlink scheitert, Kopie zurückrollen,
    // damit ein kaputter Mount nicht bei jedem Neustart Duplikate produziert.
    await fs.copyFile(src, dest);
    try {
      await fs.unlink(src);
    } catch (err) {
      await fs.unlink(dest).catch(() => undefined);
      throw err;
    }
  }
}