import {
  ForbiddenException,
  Injectable,
  Logger,
  NotFoundException,
} from '@nestjs/common';
import { PrismaService } from '../prisma/prisma.service';
import { forTenant } from '../prisma/prisma-tenant.extension';
import { CryptoService } from '../crypto/crypto.service';
import { CreateCalendarSourceDto } from './dto/create-calendar-source.dto';
import { UpdateCalendarSourceDto } from './dto/update-calendar-source.dto';
import { TestCalendarSourceConfigDto } from './dto/test-calendar-source-config.dto';
import { ICSProvider } from './providers/ics.provider';
import { CalDAVProvider } from './providers/caldav.provider';
import { ExchangeProvider } from './providers/exchange.provider';

/**
 * Common interface for normalized calendar events across all provider types.
 */
export interface CalendarEvent {
  id: string;
  sourceId: string;
  title: string;
  start: Date;
  end: Date;
  allDay: boolean;
  location?: string;
  description?: string;
  color?: string;
}

/**
 * Provider interface for calendar source integrations.
 * Each provider (ICS, CalDAV, Exchange) implements this contract.
 */
export interface CalendarProvider {
  fetchEvents(
    source: { url: string; username?: string; password?: string; exchangeMode?: string | null; domain?: string; id: string; color?: string | null },
    from: Date,
    to: Date,
  ): Promise<CalendarEvent[]>;

  testConnection(
    source: { url: string; username?: string; password?: string; exchangeMode?: string | null; domain?: string; id: string },
  ): Promise<boolean>;
}

/**
 * Prisma `select` for safe source responses — NEVER includes encryptedPassword.
 * T-05-09: Return hasCredentials boolean instead.
 */
const SOURCE_SAFE_SELECT = {
  id: true,
  userId: true,
  tenantId: true,
  name: true,
  type: true,
  exchangeMode: true,
  domain: true,
  url: true,
  username: true,
  // encryptedPassword: NEVER included — T-05-09
  color: true,
  isVisible: true,
  syncIntervalMin: true,
  lastSyncAt: true,
  lastSyncError: true,
  createdAt: true,
  updatedAt: true,
} as const;

/**
 * Private IP ranges for SSRF protection (T-05-11).
 */
const PRIVATE_IP_PATTERNS = [
  /^10\.\d{1,3}\.\d{1,3}\.\d{1,3}$/,
  /^192\.168\.\d{1,3}\.\d{1,3}$/,
  /^127\.\d{1,3}\.\d{1,3}\.\d{1,3}$/,
  /^169\.254\.\d{1,3}\.\d{1,3}$/,
  /^172\.(1[6-9]|2\d|3[0-1])\.\d{1,3}\.\d{1,3}$/,
  /^0\.0\.0\.0$/,
  /^\[::1\]$/,
  /^\[fc00:/,
  /^\[fd00:/,
  /^\[fe80:/,
];

/**
 * In-memory event cache entry with TTL (Pitfall 4).
 */
interface CacheEntry {
  events: CalendarEvent[];
  expiresAt: number;
}

/** Cache TTL in milliseconds (5 minutes). */
const CACHE_TTL_MS = 5 * 60 * 1000;

/**
 * Service for calendar source CRUD and event aggregation.
 *
 * Source config is per-user AND per-tenant bound (Mandantentrennung Etappe
 * 2, 260911-cwh) — `CalendarSource` carries a mandatory `tenantId`
 * (D-09/T-05-*: per-user ownership; row-level security: per-tenant
 * isolation). Every method with database access binds its own
 * `tenantPrisma` via `forTenant()`.
 *
 * The three ownership checks (`updateSource`/`deleteSource`/
 * `testConnection`, comparing `existing.userId` against the calling user)
 * are kept UNCHANGED alongside the binding, not replaced by it: the RLS
 * policy on `CalendarSource` carried no user dimension when measured
 * 260911-cwh, Aufgabe 1 (`calendarsource-fremder-nutzer-desselben-mandanten-gebunden-sichtbar`),
 * so a colleague of the SAME tenant would otherwise see and modify a
 * fellow user's encrypted Exchange/CalDAV credentials.
 *
 * Nachtrag (260911-nke, Etappe 3b): seit Migration 20260911120000 traegt die
 * `tenant_isolation_policy` auf `CalendarSource` die Benutzerdimension
 * (`current_user_id() IS NULL OR "userId" = current_user_id()`) — jeder
 * `forTenant()`-Aufruf oben reicht `userId` als drittes Argument durch. Die
 * drei anwendungsseitigen Besitzpruefungen bleiben trotzdem UNVERAENDERT
 * bestehen: die Datenbankregel ist ein ZWEITES Netz, kein Ersatz dafuer, und
 * ein Aufrufer, der `userId` vergisst, saehe ohne sie den ganzen Mandanten
 * (siehe .planning/WINDOWS.md).
 *
 * Credentials encrypted at rest via CryptoService (T-05-10).
 */
@Injectable()
export class CalendarService {
  private readonly logger = new Logger(CalendarService.name);

  /**
   * Per-user event cache with TTL (Pitfall 4). Key: `userId:from:to`.
   *
   * Cache-key judgment (260911-cwh, Aufgabe 1, Befund F — chain checked
   * link by link at execution time): `userId` here is `User.id`
   * (`apps/api/prisma/schema.prisma`, `model User`, `@id @default(uuid())`),
   * reached via `calendar.controller.ts` `extractContext()`
   * (`req.user?.id`), which is `JwtStrategy.validate()`'s `id: payload.sub`
   * (`apps/api/src/auth/strategies/jwt.strategy.ts`), which is
   * `sub: user.id` at token-issue time (`apps/api/src/auth/auth.service.ts`,
   * lines 143/332) — the database identity, not a login name. The
   * Etappe-3-Entscheidung (1) (tenant-scoped uniqueness for
   * `User.username`/`User.email`) does NOT touch `User.id`, which remains
   * a platform-wide UUID no tenant can share. The key therefore stays
   * without a tenant component. If any link of this chain changes, the key
   * needs a tenant component — the decision follows the measurement, not
   * this comment.
   */
  private readonly eventCache = new Map<string, CacheEntry>();

  constructor(
    private readonly prisma: PrismaService,
    private readonly crypto: CryptoService,
    private readonly icsProvider: ICSProvider,
    private readonly caldavProvider: CalDAVProvider,
    private readonly exchangeProvider: ExchangeProvider,
  ) {}

  /**
   * Returns all calendar sources for a user WITHOUT encryptedPassword.
   * Adds a `hasCredentials` boolean so the UI knows if credentials are set.
   */
  async getSources(userId: string, tenantId: string) {
    const tenantPrisma = forTenant(this.prisma, tenantId, userId);
    const sources = await tenantPrisma.calendarSource.findMany({
      where: { userId },
      select: {
        ...SOURCE_SAFE_SELECT,
        encryptedPassword: true, // Need it only to derive hasCredentials
      },
      orderBy: { createdAt: 'asc' },
    });

    return sources.map(({ encryptedPassword, ...source }) => ({
      ...source,
      hasCredentials: !!encryptedPassword,
    }));
  }

  /**
   * Creates a new calendar source. Encrypts password before storage.
   * T-05-11: Validates URL against private IP ranges (SSRF).
   */
  async addSource(userId: string, tenantId: string, dto: CreateCalendarSourceDto) {
    // Exchange EWS servers are commonly on internal networks — SSRF check skipped for exchange type
    if (dto.type !== 'exchange') await this.validateUrlNotPrivate(dto.url);

    const data: Record<string, unknown> = {
      userId,
      tenantId,
      name: dto.name,
      type: dto.type,
      url: dto.url,
      username: dto.username ?? null,
      exchangeMode: dto.exchangeMode ?? null,
      domain: dto.domain ?? null,
      color: dto.color ?? '#3B82F6',
    };

    if (dto.password) {
      data.encryptedPassword = this.crypto.encrypt(dto.password);
    }

    const tenantPrisma = forTenant(this.prisma, tenantId, userId);
    const created = await tenantPrisma.calendarSource.create({
      data: data as any,
      select: SOURCE_SAFE_SELECT,
    });

    return { ...created, hasCredentials: !!dto.password };
  }

  /**
   * Updates a calendar source. Ownership check ensures user can only modify their own sources.
   * Re-encrypts password if provided; T-05-12 ownership enforcement.
   */
  async updateSource(id: string, userId: string, tenantId: string, dto: UpdateCalendarSourceDto) {
    const tenantPrisma = forTenant(this.prisma, tenantId, userId);
    const existing = await tenantPrisma.calendarSource.findUnique({
      where: { id },
      select: { userId: true, type: true },
    });

    if (!existing) {
      throw new NotFoundException('Calendar source not found');
    }
    if (existing.userId !== userId) {
      throw new ForbiddenException('Not your calendar source');
    }

    const effectiveType = dto.type ?? existing.type;
    // Exchange EWS servers are commonly on internal networks — SSRF check skipped for exchange type
    if (dto.url && effectiveType !== 'exchange') {
      await this.validateUrlNotPrivate(dto.url);
    }

    const data: Record<string, unknown> = {};
    if (dto.name !== undefined) data.name = dto.name;
    if (dto.type !== undefined) data.type = dto.type;
    if (dto.url !== undefined) data.url = dto.url;
    if (dto.username !== undefined) data.username = dto.username;
    if (dto.exchangeMode !== undefined) data.exchangeMode = dto.exchangeMode;
    if (dto.domain !== undefined) data.domain = dto.domain;
    if (dto.color !== undefined) data.color = dto.color;
    if (dto.isVisible !== undefined) data.isVisible = dto.isVisible;

    if (dto.password !== undefined) {
      data.encryptedPassword = dto.password
        ? this.crypto.encrypt(dto.password)
        : null;
    }

    const updated = await tenantPrisma.calendarSource.update({
      where: { id },
      data: data as any,
      select: {
        ...SOURCE_SAFE_SELECT,
        encryptedPassword: true,
      },
    });

    const { encryptedPassword, ...safe } = updated;
    return { ...safe, hasCredentials: !!encryptedPassword };
  }

  /**
   * Deletes a calendar source. Ownership check enforced (T-05-12).
   */
  async deleteSource(id: string, userId: string, tenantId: string) {
    const tenantPrisma = forTenant(this.prisma, tenantId, userId);
    const existing = await tenantPrisma.calendarSource.findUnique({
      where: { id },
      select: { userId: true },
    });

    if (!existing) {
      throw new NotFoundException('Calendar source not found');
    }
    if (existing.userId !== userId) {
      throw new ForbiddenException('Not your calendar source');
    }

    await tenantPrisma.calendarSource.delete({ where: { id } });
    return { deleted: true };
  }

  /**
   * Test connection to a calendar source via its provider.
   * Updates lastSyncAt/lastSyncError on the source record.
   */
  async testConnection(id: string, userId: string, tenantId: string): Promise<{ success: boolean; error?: string }> {
    const tenantPrisma = forTenant(this.prisma, tenantId, userId);
    const source = await tenantPrisma.calendarSource.findUnique({ where: { id } });
    if (!source) throw new NotFoundException('Calendar source not found');
    if (source.userId !== userId) throw new ForbiddenException('Not your calendar source');

    const provider = this.getProvider(source.type);
    const decryptedSource = {
      url: source.url,
      username: source.username ?? undefined,
      password: source.encryptedPassword
        ? this.crypto.decrypt(source.encryptedPassword)
        : undefined,
      exchangeMode: source.exchangeMode,
      domain: source.domain ?? undefined,
      id: source.id,
    };

    try {
      const success = await provider.testConnection(decryptedSource);

      await tenantPrisma.calendarSource.update({
        where: { id },
        data: {
          lastSyncAt: success ? new Date() : undefined,
          lastSyncError: success ? null : 'Connection test failed',
        },
      });

      return { success };
    } catch {
      const errorMsg = 'Connection failed'; // T-05-13: generic error, no credentials
      await tenantPrisma.calendarSource.update({
        where: { id },
        data: { lastSyncError: errorMsg },
      });
      return { success: false, error: errorMsg };
    }
  }

  /**
   * Tests a calendar source configuration without saving it to the database.
   * Used by the "Test connection" button in the form before the source is created.
   */
  async testConnectionFromConfig(
    dto: TestCalendarSourceConfigDto,
  ): Promise<{ success: boolean; error?: string }> {
    try {
      // Exchange EWS servers are commonly on internal networks — SSRF check skipped for exchange type
      if (dto.type !== 'exchange') await this.validateUrlNotPrivate(dto.url);
    } catch (e: any) {
      return { success: false, error: e?.message ?? 'URL not allowed' };
    }

    const provider = this.getProvider(dto.type);
    const tempSource = {
      url: dto.url,
      username: dto.username,
      password: dto.password,
      exchangeMode: dto.exchangeMode ?? null,
      domain: dto.domain,
      id: 'test-config',
    };

    try {
      const success = await provider.testConnection(tempSource);
      return { success };
    } catch {
      return { success: false, error: 'Connection failed' };
    }
  }

  /**
   * Aggregate events from all visible sources for a user (CAL-02/CAL-03).
   *
   * - Loads only isVisible: true sources
   * - Decrypts credentials per source
   * - Fetches in parallel with Promise.allSettled (one failing source doesn't break others)
   * - Merges + sorts by start ascending
   * - Caches per user with 5-minute TTL (Pitfall 4)
   */
  async aggregateEvents(
    userId: string,
    tenantId: string,
    from?: string,
    to?: string,
  ): Promise<CalendarEvent[]> {
    const now = new Date();
    const fromDate = from ? new Date(from) : now;
    const toDate = to ? new Date(to) : new Date(now.getTime() + 30 * 24 * 60 * 60 * 1000); // Default: +30 days

    // Check cache first
    const cacheKey = `${userId}:${fromDate.toISOString()}:${toDate.toISOString()}`;
    const cached = this.eventCache.get(cacheKey);
    if (cached && cached.expiresAt > Date.now()) {
      // Serve cached immediately, trigger background refresh if close to expiry
      if (cached.expiresAt - Date.now() < CACHE_TTL_MS / 2) {
        this.refreshCacheInBackground(userId, tenantId, fromDate, toDate, cacheKey);
      }
      return cached.events;
    }

    // Fetch fresh
    const events = await this.fetchAndCacheEvents(userId, tenantId, fromDate, toDate, cacheKey);
    return events;
  }

  /**
   * Fetches events from all visible sources, caches them, and returns.
   */
  private async fetchAndCacheEvents(
    userId: string,
    tenantId: string,
    from: Date,
    to: Date,
    cacheKey: string,
  ): Promise<CalendarEvent[]> {
    const tenantPrisma = forTenant(this.prisma, tenantId, userId);
    const sources = await tenantPrisma.calendarSource.findMany({
      where: { userId, isVisible: true },
    });

    if (sources.length === 0) return [];

    // Fetch from all sources in parallel — Promise.allSettled so one failure doesn't break others
    const results = await Promise.allSettled(
      sources.map(async (source) => {
        const provider = this.getProvider(source.type);
        const decryptedSource = {
          url: source.url,
          username: source.username ?? undefined,
          password: source.encryptedPassword
            ? this.crypto.decrypt(source.encryptedPassword)
            : undefined,
          exchangeMode: source.exchangeMode,
          domain: source.domain ?? undefined,
          id: source.id,
          color: source.color,
        };

        try {
          const events = await provider.fetchEvents(decryptedSource, from, to);

          // Update sync status on success
          await tenantPrisma.calendarSource.update({
            where: { id: source.id },
            data: { lastSyncAt: new Date(), lastSyncError: null },
          });

          return events;
        } catch (error) {
          // Update sync error — generic message (T-05-13)
          this.logger.warn(
            `Failed to fetch events from source ${source.id} (${source.type}): ${(error as Error).message}`,
          );
          await tenantPrisma.calendarSource.update({
            where: { id: source.id },
            data: { lastSyncError: 'Event fetch failed' },
          });
          return [] as CalendarEvent[];
        }
      }),
    );

    // Merge all successful results
    const allEvents: CalendarEvent[] = [];
    for (const result of results) {
      if (result.status === 'fulfilled') {
        allEvents.push(...result.value);
      }
    }

    // Sort by start ascending
    allEvents.sort((a, b) => a.start.getTime() - b.start.getTime());

    // Cache result
    this.eventCache.set(cacheKey, {
      events: allEvents,
      expiresAt: Date.now() + CACHE_TTL_MS,
    });

    return allEvents;
  }

  /**
   * Refreshes cache in the background without blocking the response.
   *
   * This is a request context that outlives the request (Befund B,
   * 260911-cwh): it is NOT the "read across tenants, then bind per tenant"
   * shape of the background-service section in
   * docs/mandantentrennung-zugriffsklassifikation.md — it carries the
   * tenant of the ORIGINAL request that triggered it (`aggregateEvents`)
   * and cannot have any other tenant, because it never reads across
   * tenants in the first place.
   */
  private refreshCacheInBackground(
    userId: string,
    tenantId: string,
    from: Date,
    to: Date,
    cacheKey: string,
  ): void {
    this.fetchAndCacheEvents(userId, tenantId, from, to, cacheKey).catch((error) => {
      this.logger.warn(`Background cache refresh failed: ${(error as Error).message}`);
    });
  }

  /**
   * Returns the provider instance for a given source type.
   */
  private getProvider(type: string): CalendarProvider {
    switch (type) {
      case 'ics':
        return this.icsProvider;
      case 'caldav':
        return this.caldavProvider;
      case 'exchange':
        return this.exchangeProvider;
      default:
        throw new Error(`Unknown calendar source type: ${type}`);
    }
  }

  /**
   * Decrypts stored credentials for a source (used internally by providers).
   * NEVER expose this in API responses.
   */
  decryptSourcePassword(encryptedPassword: string): string {
    return this.crypto.decrypt(encryptedPassword);
  }

  /**
   * SSRF protection: reject URLs that resolve to private IP ranges.
   * T-05-11: Combined with https-only DTO validation.
   */
  private async validateUrlNotPrivate(url: string): Promise<void> {
    try {
      const parsed = new URL(url);
      const hostname = parsed.hostname;

      // Check against private IP patterns
      for (const pattern of PRIVATE_IP_PATTERNS) {
        if (pattern.test(hostname)) {
          throw new ForbiddenException(
            'Calendar source URL must not point to private/internal networks',
          );
        }
      }

      // Also block localhost variants
      if (
        hostname === 'localhost' ||
        hostname === 'ip6-localhost' ||
        hostname.endsWith('.local') ||
        hostname.endsWith('.internal')
      ) {
        throw new ForbiddenException(
          'Calendar source URL must not point to localhost or local networks',
        );
      }
    } catch (error) {
      if (error instanceof ForbiddenException) throw error;
      throw new ForbiddenException('Invalid calendar source URL');
    }
  }
}