import { Controller, Get, Inject, Query, Req, Res } from '@nestjs/common';
import type { Request, Response } from 'express';
import { Logger } from 'nestjs-pino';
import { readSessionTimeouts, sessionCookieName } from '../session/session-cookie';
import { UserSessionIndexService } from '../session/user-session-index.service';
import {
  PRE_AUTH_COOKIE_NAME,
  clearPreAuthCookieOptions,
  preAuthCookieOptions,
} from './auth.cookie';
import { AuthCodeFlowException, type AuthCodeFlowError, authErrorCode } from './auth.errors';
import { AuthService, type AuthenticatedUser, type PreAuthPayload } from './auth.service';
import { ENTRA_CONFIG, type EntraConfig } from './entra-config.token';

/**
 * OIDC routes mounted under `/api/auth/` per ADR-0009.
 *
 * Routes shipped here: `GET /login`, `GET /callback`, `GET /me`,
 * `GET /logout`. The callback persists the resolved identity into
 * the express-session store (ADR-0010); `/me` reads it back; the
 * logout endpoint destroys the session, clears the cookie, and
 * redirects to Entra's RP-initiated logout endpoint so the user is
 * signed out at the IdP too.
 */
@Controller('auth')
export class AuthController {
  constructor(
    private readonly authService: AuthService,
    private readonly logger: Logger,
    @Inject(ENTRA_CONFIG) private readonly entra: EntraConfig,
    private readonly userSessionIndex: UserSessionIndexService,
  ) {}

  /**
   * Starts the auth flow. Generates a fresh state + PKCE pair via
   * `AuthService`, stashes them in a short-lived signed cookie so
   * `/callback` can verify the round-trip, and 302s the browser to
   * Entra's authorize endpoint.
   *
   * The cookie carries everything the callback needs — no
   * server-side state. That keeps `/login` stateless and friendly
   * to horizontal scaling once the BFF runs more than one instance.
   */
  @Get('login')
  async login(@Res() res: Response): Promise<void> {
    const { authUrl, preAuthPayload } = await this.authService.beginAuthCodeFlow();
    res.cookie(PRE_AUTH_COOKIE_NAME, JSON.stringify(preAuthPayload), preAuthCookieOptions());
    res.redirect(302, authUrl);
  }

  /**
   * Second leg of the OIDC flow. Entra redirects the user here with
   * `?code=…&state=…` (success) or `?error=…&error_description=…`
   * (failure). The pre-auth cookie set by `/login` carries the
   * matching state + PKCE verifier so we can verify the round-trip
   * and finish the token exchange.
   *
   * On success, the user identity is logged via Pino and the
   * browser is redirected to the SPA. No session is persisted yet —
   * that's the next PR (Redis-backed sessions per ADR-0010); until
   * then the SPA cannot tell the user is "logged in".
   *
   * On failure (any branch — state mismatch, expired cookie,
   * missing `amr` per ADR-0011, MSAL token-exchange error, or
   * Entra-side error from the query) the user lands on the SPA
   * with `?auth_error=<code>` so the front-end can surface a
   * specific message. The pre-auth cookie is cleared on every
   * exit path: it is single-use by design.
   */
  @Get('callback')
  async callback(
    @Req() req: Request,
    @Res() res: Response,
    @Query('code') code?: string,
    @Query('state') state?: string,
    @Query('error') entraError?: string,
    @Query('error_description') entraErrorDescription?: string,
  ): Promise<void> {
    // Drop the single-use cookie regardless of outcome.
    res.clearCookie(PRE_AUTH_COOKIE_NAME, clearPreAuthCookieOptions());

    // Entra signalled a failure (e.g. user cancelled the consent
    // screen, MFA challenge failed, app-registration mismatch).
    if (entraError) {
      this.logger.warn(
        {
          event: 'auth.entra_error',
          entraError,
          entraErrorDescription,
        },
        'AuthCallback',
      );
      return this.redirectWithError(res, 'token-exchange-failed');
    }

    if (typeof code !== 'string' || typeof state !== 'string') {
      return this.redirectWithError(res, 'token-exchange-failed');
    }

    const preAuth = readPreAuthCookie(req);
    if (!preAuth) {
      // No cookie → either the user opened /callback directly, or
      // their browser dropped the cookie (TTL elapsed in
      // a 3rd-party-cookie blocker, etc.). Treat as flow-expired.
      this.logger.warn({ event: 'auth.no_pre_auth_cookie' }, 'AuthCallback');
      return this.redirectWithError(res, 'flow-expired');
    }

    try {
      const user = await this.authService.completeAuthCodeFlow(code, state, preAuth);
      const now = Date.now();
      const { absoluteSeconds } = readSessionTimeouts();
      req.session.user = user;
      req.session.createdAt = now;
      // Hard ceiling per ADR-0010 §"TTL policy" — checked on every
      // request by the absolute-timeout middleware, independent of
      // idle TTL.
      req.session.absoluteExpiresAt = now + absoluteSeconds * 1000;
      // Force the save before the redirect: express-session writes
      // on response end, but the 302 we're about to emit closes the
      // response before the async store-write would otherwise
      // complete. Without this, the browser hits the SPA before
      // Redis carries the new payload.
      await saveSession(req);
      // Register the freshly-minted session id in the per-user
      // index so a future admin "logout everywhere" can enumerate
      // and revoke. Best-effort: a Redis hiccup here doesn't fail
      // sign-in (the service swallows + logs).
      await this.userSessionIndex.add(user.oid, req.sessionID);
      this.logger.log(
        {
          event: 'auth.signed_in',
          oid: user.oid,
          tid: user.tid,
          username: user.username,
          amr: user.amr,
        },
        'AuthCallback',
      );
      res.redirect(302, this.entra.postLogoutRedirectUri);
    } catch (err) {
      if (err instanceof AuthCodeFlowException) {
        this.logger.warn({ event: 'auth.flow_error', failure: err.failure }, 'AuthCallback');
        return this.redirectWithError(res, err.failure.kind);
      }
      throw err;
    }
  }

  /**
   * Read-only view of the current session for the SPA. Returns the
   * curated subset of the resolved identity — `amr` and other
   * auth-internal claims stay server-side.
   *
   * 401 (with no body beyond a `{error}` tag) on missing session
   * lets the SPA distinguish "anonymous" from any other failure;
   * the browser's session cookie was either absent, expired, or
   * pointed at a Redis key that no longer exists.
   */
  @Get('me')
  me(@Req() req: Request, @Res() res: Response): void {
    const user = req.session.user;
    if (!user) {
      res.status(401).json({ error: 'unauthenticated' });
      return;
    }
    res.json(toPublicUser(user));
  }

  /**
   * RP-initiated logout per ADR-0009. Destroys the BFF session
   * (DEL on the Redis key), clears the session cookie, then
   * redirects the browser to Entra's `/oauth2/v2.0/logout` so the
   * IdP-side session is killed too — single sign-out behaviour. The
   * post-logout redirect on the Entra end lands the user back on
   * the SPA root.
   *
   * Idempotent: if the user was already anonymous, the destroy is
   * a no-op and we redirect anyway. CSRF for v1 relies on
   * SameSite=Lax (subresource requests don't carry the cookie); a
   * dedicated CSRF middleware lands with phase-2 security.
   */
  @Get('logout')
  async logout(@Req() req: Request, @Res() res: Response): Promise<void> {
    const user = req.session.user;
    const wasAuthenticated = Boolean(user);
    const sessionId = req.sessionID;
    const logoutUrl = this.authService.buildLogoutUrl();

    // Drop the user_sessions index entry before destroy() removes
    // the session id from `req`. Skipped on already-anonymous
    // requests (nothing was ever added).
    if (user) {
      await this.userSessionIndex.remove(user.oid, sessionId);
    }

    try {
      await destroySession(req);
    } catch (err) {
      // The Redis DEL failed — log and continue. Clearing the
      // cookie still gets the user effectively logged out from the
      // BFF's point of view; the orphan Redis key will hit its idle
      // TTL on its own.
      this.logger.error(
        {
          event: 'session.destroy_failed',
          message: err instanceof Error ? err.message : String(err),
        },
        'AuthLogout',
      );
    }

    res.clearCookie(sessionCookieName(), { path: '/' });
    this.logger.log({ event: 'auth.signed_out', wasAuthenticated }, 'AuthLogout');
    res.redirect(302, logoutUrl);
  }

  private redirectWithError(res: Response, kind: AuthCodeFlowError['kind']): void {
    const url = new URL(this.entra.postLogoutRedirectUri);
    url.searchParams.set('auth_error', authErrorCode({ kind } as AuthCodeFlowError));
    res.redirect(302, url.toString());
  }
}

interface PublicUser {
  oid: string;
  tid: string;
  username: string;
  displayName: string;
}

function toPublicUser(user: AuthenticatedUser): PublicUser {
  return {
    oid: user.oid,
    tid: user.tid,
    username: user.username,
    displayName: user.displayName,
  };
}

function saveSession(req: Request): Promise<void> {
  return new Promise((resolve, reject) => {
    req.session.save((err) => (err ? reject(err) : resolve()));
  });
}

function destroySession(req: Request): Promise<void> {
  return new Promise((resolve, reject) => {
    req.session.destroy((err) => (err ? reject(err) : resolve()));
  });
}

function readPreAuthCookie(req: Request): PreAuthPayload | null {
  const raw = (req.signedCookies as Record<string, unknown>)[PRE_AUTH_COOKIE_NAME];
  if (typeof raw !== 'string') {
    return null;
  }
  try {
    const parsed = JSON.parse(raw) as Partial<PreAuthPayload>;
    if (
      typeof parsed.state === 'string' &&
      typeof parsed.codeVerifier === 'string' &&
      typeof parsed.createdAt === 'number'
    ) {
      return {
        state: parsed.state,
        codeVerifier: parsed.codeVerifier,
        createdAt: parsed.createdAt,
      };
    }
    return null;
  } catch {
    return null;
  }
}