import {
  BadRequestException,
  Injectable,
  Logger,
  NotFoundException,
} from '@nestjs/common';
import * as fs from 'fs';
import * as path from 'path';
import { CalendarCryptoService } from '../calendar/crypto.service';
import { PrismaService } from '../prisma/prisma.service';
import { DkvExportService } from './dkv-export.service';
import { DkvMailService } from './dkv-mail.service';
import { DkvParserService } from './dkv-parser.service';
import { DkvConfigDto } from './dto/dkv-config.dto';
import { CreateVehicleDto, UpdateVehicleDto } from './dto/dkv-vehicle.dto';
import { ExchangeInboxProvider } from './providers/exchange-inbox.provider';
import { ImapProvider } from './providers/imap.provider';
import type { DkvVehicleBlock, InboxConfig, InboxEmail } from './dkv.types';

/**
 * Prisma select for DkvModuleConfig — never includes encryptedInboxCreds.
 * T-07-12: Encrypted credential blob is excluded from all API responses.
 */
const CONFIG_SAFE_SELECT = {
  id: true,
  tenantId: true,
  protocol: true,
  host: true,
  port: true,
  encryption: true,
  folder: true,
  senderFilter: true,
  pollIntervalMin: true,
  isActive: true,
  exportRecipient: true,
  vehicleFormatString: true,
  // encryptedInboxCreds: NEVER included — T-07-12
  createdAt: true,
  updatedAt: true,
} as const;

/**
 * DkvService — orchestrates the full DKV processing pipeline.
 *
 * Pipeline:
 *   poll inbox → download PDF attachments → parse vehicle/transaction data
 *   → map license plates to drivers → build xlsx → write to user-files/
 *   → send via SMTP → record history
 *
 * Security:
 * - T-05-13: Decrypted credentials never logged
 * - T-07-12: CONFIG_SAFE_SELECT excludes encryptedInboxCreds in all responses
 * - T-07-09: Export filename validated against safe pattern before reading (traversal guard)
 * - Single-flight guard: prevents concurrent inbox processing (Pitfall 7)
 *
 * Multi-tenant note (v1): The scheduler loads config via findFirst().
 * Each processInbox(tenantId) call is per-tenant. The Controller scopes all
 * operations to req.tenantId. Full per-tenant scheduling (one cron per active
 * tenant) is deferred to a future plan — v1 covers single-tenant deployments.
 */
@Injectable()
export class DkvService {
  private readonly logger = new Logger(DkvService.name);

  /**
   * Single-flight guard: if processing is already in progress, any concurrent
   * call to processInbox() returns early without starting a second pipeline
   * run (Pitfall 7 — prevents the prune race condition and duplicate records).
   */
  private processing = false;

  /** Resolved path to user-files/ directory (monorepo root). */
  private readonly userFilesDir: string;

  constructor(
    private readonly prisma: PrismaService,
    private readonly crypto: CalendarCryptoService,
    private readonly parser: DkvParserService,
    private readonly exporter: DkvExportService,
    private readonly mailer: DkvMailService,
    private readonly imapProvider: ImapProvider,
    private readonly exchangeProvider: ExchangeInboxProvider,
  ) {
    // __dirname at runtime = apps/api/dist/dkv/ — go up 4 levels to monorepo root
    this.userFilesDir = path.resolve(__dirname, '..', '..', '..', '..', 'user-files');
  }

  // ─── Config ──────────────────────────────────────────────────────────────────

  /**
   * Load DKV module config for a tenant (safe — no encrypted creds).
   * When tenantId is omitted, returns the first row (used by scheduler on init).
   */
  async loadConfig(tenantId?: string) {
    if (!tenantId) {
      return this.prisma.dkvModuleConfig.findFirst({ select: CONFIG_SAFE_SELECT });
    }
    return this.prisma.dkvModuleConfig.findUnique({
      where: { tenantId },
      select: CONFIG_SAFE_SELECT,
    });
  }

  /**
   * Upsert DKV module config for a tenant.
   *
   * Credential handling:
   * - If dto.password is non-empty: re-encrypt {username, password} together.
   *   username is taken from dto.username if provided, else preserved from DB.
   * - If dto.username is non-empty but dto.password is empty: preserve existing
   *   password; re-encrypt with new username.
   * - If both are empty/undefined: preserve existing encryptedInboxCreds entirely.
   *
   * T-07-12: Returns safe select (no encryptedInboxCreds).
   * T-05-13: Never logs decrypted credentials.
   */
  async saveConfig(tenantId: string, dto: DkvConfigDto) {
    let encryptedInboxCreds: string | undefined;

    const credChanged = (dto.password && dto.password.length > 0) ||
      (dto.username !== undefined && dto.username !== null);

    if (credChanged) {
      let username: string = dto.username ?? '';
      let password: string = dto.password ?? '';

      // Preserve the field that was left empty from the existing stored value
      if (!dto.password || !dto.username) {
        try {
          const existing = await this.prisma.dkvModuleConfig.findUnique({ where: { tenantId } });
          if (existing?.encryptedInboxCreds) {
            // T-05-13: decrypt only to preserve — never log the result
            const stored = JSON.parse(this.crypto.decrypt(existing.encryptedInboxCreds)) as {
              username?: string;
              password?: string;
            };
            if (!dto.username) username = stored.username ?? '';
            if (!dto.password) password = stored.password ?? '';
          }
        } catch {
          // Ignore decrypt errors — will overwrite with whatever was provided
        }
      }

      encryptedInboxCreds = this.crypto.encrypt(JSON.stringify({ username, password }));
    }

    const data: Record<string, unknown> = {
      protocol: dto.protocol,
      encryption: dto.encryption,
      ...(dto.host !== undefined && { host: dto.host }),
      ...(dto.port !== undefined && { port: dto.port }),
      ...(dto.folder !== undefined && { folder: dto.folder }),
      ...(dto.senderFilter !== undefined && { senderFilter: dto.senderFilter }),
      ...(dto.pollIntervalMin !== undefined && { pollIntervalMin: dto.pollIntervalMin }),
      ...(dto.isActive !== undefined && { isActive: dto.isActive }),
      ...(dto.exportRecipient !== undefined && { exportRecipient: dto.exportRecipient }),
      ...(dto.vehicleFormatString !== undefined && { vehicleFormatString: dto.vehicleFormatString }),
      ...(encryptedInboxCreds !== undefined && { encryptedInboxCreds }),
    };

    return this.prisma.dkvModuleConfig.upsert({
      where: { tenantId },
      create: { tenantId, ...data },
      update: data,
      select: CONFIG_SAFE_SELECT,
    });
  }

  /**
   * Test the inbox connection using credentials from the form DTO.
   * When dto.password is empty, falls back to the stored encrypted password.
   *
   * T-05-13: Decrypted password used only within this method scope — never logged.
   */
  async testConnection(tenantId: string, dto: DkvConfigDto): Promise<boolean> {
    let password: string | undefined = dto.password;

    // If no password in DTO, fall back to the stored one
    if (!password) {
      try {
        const existing = await this.prisma.dkvModuleConfig.findUnique({ where: { tenantId } });
        if (existing?.encryptedInboxCreds) {
          const stored = JSON.parse(this.crypto.decrypt(existing.encryptedInboxCreds)) as {
            password?: string;
          };
          password = stored.password;
        }
      } catch {
        // T-05-13: generic — no credential details
        this.logger.error(`DKV testConnection: failed to load stored credentials for tenant ${tenantId}`);
      }
    }

    const inboxConfig: InboxConfig = {
      protocol: dto.protocol,
      host: dto.host ?? '',
      port: dto.port ?? 993,
      username: dto.username,
      password,
      encryption: dto.encryption,
      folder: dto.folder ?? 'INBOX',
      senderFilter: dto.senderFilter,
    };

    const provider = dto.protocol === 'exchange' ? this.exchangeProvider : this.imapProvider;
    return provider.testConnection(inboxConfig);
  }

  // ─── Pipeline ─────────────────────────────────────────────────────────────────

  /**
   * Trigger an inbox check for a tenant.
   * Returns a summary object: status, message, checkedAt.
   *
   * Used by POST /dkv/check-now and indirectly by the scheduler.
   */
  async checkNow(tenantId: string): Promise<{
    status: string;
    message: string;
    checkedAt: string;
  }> {
    const checkedAt = new Date().toISOString();
    try {
      await this.processInbox(tenantId);
      return { status: 'ok', message: 'Posteingang geprüft', checkedAt };
    } catch (err) {
      return {
        status: 'error',
        message: (err as Error).message,
        checkedAt,
      };
    }
  }

  /**
   * Run the full DKV inbox processing pipeline for a tenant.
   *
   * Single-flight guard: returns early if already processing (Pitfall 7).
   * Pipeline: load config → decrypt creds → fetch PDFs → parse → map drivers
   *           → build xlsx → write to user-files/ → send SMTP → record history.
   */
  async processInbox(tenantId: string): Promise<void> {
    if (this.processing) {
      this.logger.warn(`DKV inbox already processing for tenant ${tenantId} — skipping`);
      return;
    }
    this.processing = true;

    try {
      await this._runPipeline(tenantId);
    } finally {
      this.processing = false;
    }
  }

  private async _runPipeline(tenantId: string): Promise<void> {
    // Load raw config (need encryptedInboxCreds for decryption)
    const config = await this.prisma.dkvModuleConfig.findUnique({ where: { tenantId } });
    if (!config) {
      this.logger.warn(`DKV processInbox: no config for tenant ${tenantId}`);
      return;
    }
    if (!config.isActive) {
      this.logger.log(`DKV inbox polling is inactive for tenant ${tenantId}`);
      return;
    }

    // Decrypt inbox credentials — T-05-13: never log result
    let inboxConfig: InboxConfig;
    try {
      const creds = config.encryptedInboxCreds
        ? (JSON.parse(this.crypto.decrypt(config.encryptedInboxCreds)) as {
            username?: string;
            password?: string;
          })
        : {};

      inboxConfig = {
        protocol: config.protocol,
        host: config.host ?? '',
        port: config.port ?? 993,
        username: creds.username,
        password: creds.password,
        encryption: config.encryption,
        folder: config.folder,
        senderFilter: config.senderFilter ?? undefined,
      };
    } catch {
      this.logger.error(`DKV inbox config decryption failed for tenant ${tenantId}`);
      return;
    }

    // Select provider by protocol
    const provider = config.protocol === 'exchange' ? this.exchangeProvider : this.imapProvider;

    // Fetch PDF attachments from inbox
    let emails: InboxEmail[];
    try {
      emails = await provider.fetchPdfAttachments(inboxConfig);
    } catch (err) {
      this.logger.error(
        `DKV inbox fetch failed for tenant ${tenantId}: ${(err as Error).message}`,
      );
      return;
    }

    if (emails.length === 0) {
      this.logger.log(`DKV inbox check: no matching emails for tenant ${tenantId}`);
      return;
    }

    const vehicleFormatString = config.vehicleFormatString ?? '{Marke}/{Modell}/{Kennzeichen}';

    for (const email of emails) {
      for (const attachment of email.attachments) {
        await this._processAttachment(
          tenantId,
          attachment.buffer,
          email,
          config.exportRecipient ?? undefined,
          vehicleFormatString,
        );
      }
    }
  }

  /**
   * Process a single PDF attachment through the full pipeline.
   * D-10: Up to 3 parse retries; on final failure record Fehler history row.
   * D-16: Up to 3 SMTP send retries with exponential backoff; on final failure
   *       record Versand fehlgeschlagen (file stays locally available).
   */
  private async _processAttachment(
    tenantId: string,
    pdfBuffer: Buffer,
    email: InboxEmail,
    recipient: string | undefined,
    vehicleFormatString: string,
  ): Promise<void> {
    // D-10: Up to 3 parse retries
    let vehicles: DkvVehicleBlock[] | null = null;
    let parseError: string | null = null;

    for (let attempt = 1; attempt <= 3; attempt++) {
      try {
        vehicles = await this.parser.parsePdf(pdfBuffer);
        parseError = null;
        break;
      } catch (err) {
        parseError = (err as Error).message;
        this.logger.warn(
          `DKV PDF parse attempt ${attempt}/3 for tenant ${tenantId}: ${parseError}`,
        );
      }
    }

    if (!vehicles) {
      // Record parse failure in history (D-10)
      await this.prisma.dkvInvoiceHistory.create({
        data: {
          tenantId,
          rechnungsnummer: this._extractInvoiceNumber(email.subject, email.uid),
          anzahlFahrzeuge: 0,
          anzahlTransaktionen: 0,
          status: 'Fehler',
          errorMessage: parseError ?? 'PDF parse failed',
        },
      });
      return;
    }

    // Extract invoice metadata for filename + history record
    const rechnungsnummer = this._extractInvoiceNumber(email.subject, email.uid);
    const invoiceMonth = this._extractInvoiceMonth(vehicles);
    const anzahlTransaktionen = vehicles.reduce((s, v) => s + v.transactions.length, 0);

    // Build export rows — look up drivers from vehicle master
    const exportRows = await this._buildExportRows(tenantId, vehicles, vehicleFormatString);

    // Generate xlsx buffer and write to user-files/ (DkvExportService)
    const xlsxBuffer = this.exporter.buildExcelBuffer(exportRows);
    const exportFilename = this.exporter.writeAndPrune(xlsxBuffer, rechnungsnummer, invoiceMonth);

    // D-16: SMTP send with 3-retry exponential backoff
    let smtpStatus: 'Verarbeitet' | 'Versand fehlgeschlagen' = 'Verarbeitet';
    let smtpError: string | undefined;

    if (recipient) {
      for (let attempt = 1; attempt <= 3; attempt++) {
        try {
          await this.mailer.sendExportEmail(tenantId, recipient, xlsxBuffer, exportFilename);
          smtpStatus = 'Verarbeitet';
          smtpError = undefined;
          break;
        } catch (err) {
          smtpError = (err as Error).message;
          this.logger.warn(`DKV SMTP send attempt ${attempt}/3 failed: ${smtpError}`);
          if (attempt < 3) {
            await _delay(Math.pow(2, attempt) * 1000); // 2s, 4s
          } else {
            smtpStatus = 'Versand fehlgeschlagen';
            // D-16: file stays locally available for manual download
          }
        }
      }
    } else {
      // No recipient configured — mark as processed without sending
      this.logger.warn(`DKV: no exportRecipient configured for tenant ${tenantId} — skipping SMTP send`);
    }

    // Record history row (D-20)
    await this.prisma.dkvInvoiceHistory.create({
      data: {
        tenantId,
        rechnungsnummer,
        anzahlFahrzeuge: vehicles.length,
        anzahlTransaktionen,
        status: smtpStatus,
        ...(smtpError && { errorMessage: smtpError }),
        exportFilename,
      },
    });

    this.logger.log(
      `DKV processed: ${rechnungsnummer} — ${vehicles.length} vehicles, ${anzahlTransaktionen} transactions, status: ${smtpStatus}`,
    );
  }

  // ─── Vehicle CRUD ────────────────────────────────────────────────────────────

  async listVehicles(tenantId: string) {
    return this.prisma.dkvVehicleMaster.findMany({
      where: { tenantId },
      orderBy: { kennzeichen: 'asc' },
    });
  }

  async createVehicle(tenantId: string, dto: CreateVehicleDto) {
    return this.prisma.dkvVehicleMaster.create({
      data: { tenantId, ...dto },
    });
  }

  async updateVehicle(tenantId: string, id: string, dto: UpdateVehicleDto) {
    const existing = await this.prisma.dkvVehicleMaster.findFirst({
      where: { id, tenantId },
    });
    if (!existing) throw new NotFoundException('Vehicle not found');
    return this.prisma.dkvVehicleMaster.update({ where: { id }, data: dto });
  }

  async deleteVehicle(tenantId: string, id: string): Promise<{ deleted: boolean }> {
    const existing = await this.prisma.dkvVehicleMaster.findFirst({
      where: { id, tenantId },
    });
    if (!existing) throw new NotFoundException('Vehicle not found');
    await this.prisma.dkvVehicleMaster.delete({ where: { id } });
    return { deleted: true };
  }

  /**
   * Bulk-import vehicles from semicolon-delimited CSV text.
   *
   * CSV header (case-insensitive): Kennzeichen;Marke;Modell;Fahrer
   *
   * mode='merge': upsert each vehicle (add new, update existing by Kennzeichen).
   * mode='replace': delete all existing vehicles for this tenant, then insert.
   *
   * Research pattern: CSV Vehicle Import Pattern (RESEARCH.md Code Examples).
   */
  async importVehiclesCsv(
    tenantId: string,
    csvText: string,
    mode: 'merge' | 'replace',
  ): Promise<{ imported: number; mode: string }> {
    const vehicles = _parseVehicleCsv(csvText);
    if (vehicles.length === 0) {
      throw new BadRequestException(
        'CSV enthält keine gültigen Fahrzeuge. Erwarteter Header: Kennzeichen;Marke;Modell;Fahrer',
      );
    }

    if (mode === 'replace') {
      await this.prisma.dkvVehicleMaster.deleteMany({ where: { tenantId } });
      await this.prisma.dkvVehicleMaster.createMany({
        data: vehicles.map((v) => ({ tenantId, ...v })),
      });
    } else {
      // Merge: upsert by (tenantId, kennzeichen) compound unique key
      for (const v of vehicles) {
        await this.prisma.dkvVehicleMaster.upsert({
          where: { tenantId_kennzeichen: { tenantId, kennzeichen: v.kennzeichen } },
          create: { tenantId, ...v },
          update: { marke: v.marke, modell: v.modell, fahrer: v.fahrer },
        });
      }
    }

    this.logger.log(`DKV CSV import: ${vehicles.length} vehicles, mode=${mode}, tenant=${tenantId}`);
    return { count: vehicles.length, mode };
  }

  // ─── History ─────────────────────────────────────────────────────────────────

  /**
   * Get paginated processing history for a tenant.
   * Ordered by datumZeit descending (most recent first).
   * T-07-06: pagination prevents unbounded result-set DoS.
   */
  async getHistory(
    tenantId: string,
    page = 1,
    limit = 20,
  ): Promise<{
    items: unknown[];
    total: number;
    page: number;
    limit: number;
  }> {
    const skip = (page - 1) * limit;
    const [items, total] = await Promise.all([
      this.prisma.dkvInvoiceHistory.findMany({
        where: { tenantId },
        orderBy: { datumZeit: 'desc' },
        skip,
        take: limit,
      }),
      this.prisma.dkvInvoiceHistory.count({ where: { tenantId } }),
    ]);
    return { items, total, page, limit };
  }

  // ─── Export file download ────────────────────────────────────────────────────

  /**
   * Read a DKV export file from user-files/ and return its Buffer.
   *
   * T-07-09 traversal guard: validates filename against the server-generated
   * pattern `DKV_*.xlsx` before reading. Rejects any filename containing path
   * separators, `..`, or characters outside the expected character set.
   *
   * @throws BadRequestException when filename fails validation
   * @throws NotFoundException when the file does not exist
   */
  async getExportFile(tenantId: string, filename: string): Promise<Buffer> {
    // Traversal guard: whitelist-validate the filename before reading
    if (
      filename.includes('/') ||
      filename.includes('\\') ||
      filename.includes('..') ||
      !/^DKV_[\w\-]+\.xlsx$/.test(filename)
    ) {
      throw new BadRequestException('Invalid export filename');
    }

    const filePath = path.join(this.userFilesDir, filename);

    if (!fs.existsSync(filePath)) {
      throw new NotFoundException(`Export file not found: ${filename}`);
    }

    return fs.readFileSync(filePath);
  }

  // ─── Private helpers ──────────────────────────────────────────────────────────

  /**
   * Build ExportRow[] for the xlsx generator by looking up each vehicle's driver.
   *
   * Vehicles with no matching DkvVehicleMaster entry still appear in the export
   * with an empty Fahrer field (D-13). The Fahrzeug column is resolved via the
   * format string with empty Marke/Modell/Fahrer placeholders for unknown plates.
   */
  private async _buildExportRows(
    tenantId: string,
    vehicles: DkvVehicleBlock[],
    vehicleFormatString: string,
  ): Promise<{ lieferdatum: string; fahrzeug: string; fahrer: string; ort: string; kilometerstand: number }[]> {
    // Batch load vehicle master to avoid N+1 queries
    const masters = await this.prisma.dkvVehicleMaster.findMany({ where: { tenantId } });
    const masterMap = new Map(masters.map((m) => [m.kennzeichen, m]));

    const rows: { lieferdatum: string; fahrzeug: string; fahrer: string; ort: string; kilometerstand: number }[] = [];

    for (const vehicle of vehicles) {
      const master = masterMap.get(vehicle.kennzeichen);

      // For unknown plates: use empty string values for unknown fields
      const vehicleForFormat = {
        kennzeichen: vehicle.kennzeichen,
        marke: master?.marke ?? '',
        modell: master?.modell ?? '',
        fahrer: master?.fahrer ?? '',
      };

      const fahrzeug = this.exporter.resolveFahrzeug(vehicleForFormat, vehicleFormatString);
      const fahrer = master?.fahrer ?? '';

      for (const tx of vehicle.transactions) {
        rows.push({
          lieferdatum: tx.lieferdatum,
          fahrzeug,
          fahrer,
          ort: tx.ort,
          kilometerstand: tx.kilometerstand,
        });
      }
    }

    return rows;
  }

  /**
   * Extract a DKV invoice number from the email subject line.
   * Pattern: DD-DDDDDDDDD-DDD (e.g. "26-651566449-001")
   * Falls back to "email-{uid}" when no match is found.
   */
  private _extractInvoiceNumber(subject: string, uid: number | string): string {
    const match = subject?.match(/(\d{2}-\d{9}-\d{3})/);
    if (match?.[1]) return match[1];
    // Fallback when invoice number cannot be parsed from subject
    return `email-${String(uid)}`;
  }

  /**
   * Derive the invoice month (YYYY-MM) from the first transaction date.
   * DKV dates are "DD.MM.YYYY" — this converts to "YYYY-MM" for the filename.
   * Falls back to the current month when no transaction date is available.
   */
  private _extractInvoiceMonth(vehicles: DkvVehicleBlock[]): string {
    const firstDate = vehicles[0]?.transactions[0]?.lieferdatum;
    if (firstDate) {
      const parts = firstDate.split('.');
      if (parts.length === 3) return `${parts[2]}-${parts[1]}`;
    }
    return new Date().toISOString().slice(0, 7);
  }
}

// ─── Module-level helpers ────────────────────────────────────────────────────

/**
 * Parse semicolon-delimited CSV into vehicle master records.
 * Expected header: Kennzeichen;Marke;Modell;Fahrer (case-insensitive).
 * Skips rows with empty Kennzeichen.
 *
 * Research: CSV Vehicle Import Pattern (RESEARCH.md Code Examples).
 */
function _parseVehicleCsv(
  csvText: string,
): { kennzeichen: string; marke: string; modell: string; fahrer: string }[] {
  const lines = csvText
    .trim()
    .split('\n')
    .map((l) => l.trim())
    .filter(Boolean);

  if (lines.length < 2) return [];

  const headers = lines[0].split(';').map((h) => h.trim().toLowerCase());

  return lines
    .slice(1)
    .map((line) => {
      const cols = line.split(';').map((c) => c.trim());
      return {
        kennzeichen: cols[headers.indexOf('kennzeichen')] ?? '',
        marke: cols[headers.indexOf('marke')] ?? '',
        modell: cols[headers.indexOf('modell')] ?? '',
        fahrer: cols[headers.indexOf('fahrer')] ?? '',
      };
    })
    .filter((v) => v.kennzeichen.length > 0);
}

/** Simple promise-based delay for retry backoff. */
function _delay(ms: number): Promise<void> {
  return new Promise((resolve) => setTimeout(resolve, ms));
}