import { Injectable, UnauthorizedException } from '@nestjs/common';
import { APP_CONFIG, type AppConfig } from '../config/config.tokens';
import { Inject } from '@nestjs/common';
import { AuditService } from '../audit/audit.service';
import { PasswordHasher } from '../users/password-hasher';
import { UserRepository } from '../users/user.repository';
import type { AuthUser } from '../users/user.types';
import { RateLimiterService } from './rate-limiter.service';
import { SessionService, type SessionData } from './session.service';

/** Ergebnis eines erfolgreichen Logins. */
export interface LoginResult {
  readonly user: AuthUser;
  readonly sessionToken: string;
  readonly session: SessionData;
}

/** Generische Meldung – verhindert User-Enumeration. */
const INVALID_CREDENTIALS_MESSAGE = 'Benutzername oder Passwort ist falsch';

/**
 * Authentifizierungs-Logik (Domain/Application):
 * Login mit Rate Limiting, Account Lockout, Argon2id-Verifikation,
 * Session-Erstellung und Audit-Logging.
 */
@Injectable()
export class AuthService {
  constructor(
    private readonly userRepository: UserRepository,
    private readonly passwordHasher: PasswordHasher,
    private readonly sessionService: SessionService,
    private readonly rateLimiter: RateLimiterService,
    private readonly auditService: AuditService,
    @Inject(APP_CONFIG) private readonly config: AppConfig,
  ) {}

  async login(input: {
    username: string;
    password: string;
    ipAddress: string | null;
  }): Promise<LoginResult> {
    const { security } = this.config;
    const rateLimitKey = `login:${input.ipAddress ?? 'unknown'}`;

    if (!this.rateLimiter.isAllowed(
      rateLimitKey,
      security.loginRateLimitAttempts,
      security.loginRateLimitWindowMinutes,
    )) {
      await this.auditService.record({
        userId: null,
        username: input.username,
        action: 'LOGIN_FAILED',
        details: { reason: 'RATE_LIMITED' },
        ipAddress: input.ipAddress,
      });
      throw new UnauthorizedException('Zu viele Anmeldeversuche. Bitte später erneut versuchen.');
    }

    const user = await this.userRepository.findByUsername(input.username);

    // Gleiches Verhalten für "unbekannter Benutzer" und "falsches Passwort"
    // (keine User-Enumeration).
    if (!user) {
      await this.auditService.record({
        userId: null,
        username: input.username,
        action: 'LOGIN_FAILED',
        details: { reason: 'UNKNOWN_USER' },
        ipAddress: input.ipAddress,
      });
      throw new UnauthorizedException(INVALID_CREDENTIALS_MESSAGE);
    }

    if (user.lockedUntil && user.lockedUntil > new Date()) {
      await this.auditService.record({
        userId: user.id,
        username: user.username,
        action: 'LOGIN_FAILED',
        details: { reason: 'ACCOUNT_LOCKED' },
        ipAddress: input.ipAddress,
      });
      throw new UnauthorizedException(INVALID_CREDENTIALS_MESSAGE);
    }

    const passwordValid = await this.passwordHasher.verify(user.passwordHash, input.password);
    if (!passwordValid) {
      const attempts = user.failedLoginAttempts + 1;
      const shouldLock = attempts >= security.loginMaxAttempts;
      await this.userRepository.updateLoginFailure(
        user.id,
        attempts,
        shouldLock,
        security.loginLockoutMinutes,
      );
      await this.auditService.record({
        userId: user.id,
        username: user.username,
        action: shouldLock ? 'LOGIN_FAILED_LOCKED' : 'LOGIN_FAILED',
        details: { reason: 'INVALID_PASSWORD', attempts },
        ipAddress: input.ipAddress,
      });
      throw new UnauthorizedException(INVALID_CREDENTIALS_MESSAGE);
    }

    if (!user.isActive) {
      await this.auditService.record({
        userId: user.id,
        username: user.username,
        action: 'LOGIN_FAILED',
        details: { reason: 'ACCOUNT_INACTIVE' },
        ipAddress: input.ipAddress,
      });
      throw new UnauthorizedException(INVALID_CREDENTIALS_MESSAGE);
    }

    await this.userRepository.updateLoginSuccess(user.id);
    this.rateLimiter.reset(rateLimitKey);

    const { token, data } = await this.sessionService.create(
      user.id,
      security.sessionTtlMinutes,
    );

    await this.auditService.record({
      userId: user.id,
      username: user.username,
      action: 'LOGIN_SUCCESS',
      ipAddress: input.ipAddress,
    });

    return {
      user: {
        id: user.id,
        username: user.username,
        email: user.email,
        displayName: user.displayName,
        role: user.role,
      },
      sessionToken: token,
      session: data,
    };
  }

  async logout(sessionId: string, user: AuthUser, ipAddress: string | null): Promise<void> {
    await this.sessionService.delete(sessionId);
    await this.auditService.record({
      userId: user.id,
      username: user.username,
      action: 'LOGOUT',
      ipAddress,
    });
  }
}