/**
 * Configuration for SAML, useful for enterprise single-sign-on logins.
 * A good informative overview of SAML is at https://www.okta.com/integrate/documentation/saml/
 * Note:
 *    SP is "Service Provider", in our case, the Grist application.
 *    IdP is the "Identity Provider", somewhere users log into, e.g. Okta or Google Apps.
 *
 * We expect IdP to provide us with name_id, a unique identifier for the user.
 * We also use optional attributes for the user's name, for which we accept any of:
 *    FirstName
 *    LastName
 *    http://schemas.xmlsoap.org/ws/2005/05/identity/claims/givenname
 *    http://schemas.xmlsoap.org/ws/2005/05/identity/claims/surname
 *
 * Note that the code is based on the example at https://github.com/Clever/saml2
 *
 * Expected environment variables:
 *    env GRIST_SAML_SP_HOST=https://<your-domain>
 *        Host at which our /saml/assert endpoint will live; identifies our application.
 *    env GRIST_SAML_SP_KEY
 *        Path to file with our private key, PEM format.
 *    env GRIST_SAML_SP_CERT
 *        Path to file with our public key, PEM format.
 *    env GRIST_SAML_IDP_LOGIN
 *        Login url to redirect user to for log-in.
 *    env GRIST_SAML_IDP_LOGOUT
 *        Logout URL to redirect user to for log-out.
 *    env GRIST_SAML_IDP_SKIP_SLO
 *        If set and non-empty, don't attempt "Single Logout" flow (which I haven't gotten to
 *        work), but simply redirect to GRIST_SAML_IDP_LOGOUT after clearing session.
 *    env GRIST_SAML_IDP_CERTS
 *        Comma-separated list of paths for certificates from identity provider, PEM format.
 *    env GRIST_SAML_IDP_UNENCRYPTED
 *        If set and non-empty, allow unencrypted assertions, relying on https for privacy.
 *
 * This version of SamlConfig has been tested with Auth0 SAML IdP following the instructions
 * at:
 *   https://auth0.com/docs/protocols/saml-protocol/configure-auth0-as-saml-identity-provider
 * When running on localhost and http, the settings tested were with:
 *   - GRIST_SAML_IDP_SKIP_SLO not set
 *   - GRIST_SAML_SP_HOST=http://localhost:8080 or 8484
 *   - GRIST_SAML_IDP_UNENCRYPTED=1
 *   - GRIST_SAML_IDP_LOGIN=https://...auth0.com/samlp/xxxx
 *   - GRIST_SAML_IDP_LOGOUT=https://...auth0.com/samlp/xxxx  # these are same for Auth0
 *   - GRIST_SAML_IDP_CERTS=.../auth0.pem   # downloaded per Auth0 instructions
 *   - GRIST_SAML_SP_KEY=.../saml.pem       # created
 *   - GRIST_SAML_SP_CERT=.../saml.crt      # created
 *
 * Created and used the key/cert pair following instructions here:
 *   https://auth0.com/docs/protocols/saml-protocol/saml-sso-integrations/sign-and-encrypt-saml-requests#use-custom-certificate-to-sign-requests
 *   https://auth0.com/docs/protocols/saml-protocol/saml-sso-integrations/sign-and-encrypt-saml-requests#auth0-as-the-saml-identity-provider
 *
 */

import * as express from 'express';
import * as fse from 'fs-extra';
import * as saml2 from 'saml2-js';

import {expressWrap} from 'app/server/lib/expressWrap';
import {GristLoginSystem, GristServer} from 'app/server/lib/GristServer';
import log from 'app/server/lib/log';
import {Permit} from 'app/server/lib/Permit';
import {getOriginUrl} from 'app/server/lib/requestUtils';
import {fromCallback} from 'app/server/lib/serverUtils';
import {Sessions} from 'app/server/lib/Sessions';

export class SamlConfig {
  private _serviceProvider: saml2.ServiceProvider;
  private _identityProvider: saml2.IdentityProvider;

  public constructor(private _gristServer: GristServer) {}

  // Read SAML certificate files and initialize the SAML state.
  public async initSaml(): Promise<void> {
    if (!process.env.GRIST_SAML_SP_HOST) { throw new Error("initSaml requires GRIST_SAML_SP_HOST to be set"); }
    if (!process.env.GRIST_SAML_SP_KEY) { throw new Error("initSaml requires GRIST_SAML_SP_KEY to be set"); }
    if (!process.env.GRIST_SAML_SP_CERT) { throw new Error("initSaml requires GRIST_SAML_SP_CERT to be set"); }
    if (!process.env.GRIST_SAML_IDP_LOGIN) { throw new Error("initSaml requires GRIST_SAML_IDP_LOGIN to be set"); }
    if (!process.env.GRIST_SAML_IDP_LOGOUT) { throw new Error("initSaml requires GRIST_SAML_IDP_LOGOUT to be set"); }
    if (!process.env.GRIST_SAML_IDP_CERTS) { throw new Error("initSaml requires GRIST_SAML_IDP_CERTS to be set"); }

    const spHost: string = process.env.GRIST_SAML_SP_HOST;
    const spOptions: saml2.ServiceProviderOptions = {
      entity_id: `${spHost}/saml/metadata.xml`,
      private_key: await fse.readFile(process.env.GRIST_SAML_SP_KEY, {encoding: 'utf8'}),
      certificate: await fse.readFile(process.env.GRIST_SAML_SP_CERT, {encoding: 'utf8'}),
      assert_endpoint: `${spHost}/saml/assert`,
      notbefore_skew: 5,      // allow 5 seconds of time skew
      sign_get_request: true  // Auth0 requires this. If it is a problem for others, could make optional.
    };
    this._serviceProvider = new saml2.ServiceProvider(spOptions);

    const idpCerts = process.env.GRIST_SAML_IDP_CERTS.split(",");
    const idpOptions: saml2.IdentityProviderOptions = {
      sso_login_url: process.env.GRIST_SAML_IDP_LOGIN,
      sso_logout_url: process.env.GRIST_SAML_IDP_LOGOUT,
      certificates: await Promise.all(idpCerts.map((p) => fse.readFile(p, {encoding: 'utf8'}))),
      // Encrypted assertions are recommended, but not necessary when over https.
      allow_unencrypted_assertion: Boolean(process.env.GRIST_SAML_IDP_UNENCRYPTED),
    };
    this._identityProvider = new saml2.IdentityProvider(idpOptions);
    log.info(`SamlConfig set with host ${spHost}, IdP ${process.env.GRIST_SAML_IDP_LOGIN}`);
  }

  // Return a login URL to which to redirect the user to log in. Once logged in, the user will be
  // redirected to redirectUrl
  public async getLoginRedirectUrl(req: express.Request, redirectUrl: URL): Promise<string> {
    const sp = this._serviceProvider;
    const idp = this._identityProvider;
    const { permit: relay_state, samlNameId } = await this._prepareAppState(req, redirectUrl, {
      action: 'login',
      waitMinutes: 20,
    });
    const force_authn = samlNameId === undefined;  // If logged out locally, ignore any
                                                   // log in state retained by IdP.
    return fromCallback((cb) => sp.create_login_request_url(idp, {relay_state, force_authn}, cb));
  }

  // Returns the URL to log the user out of SAML IdentityProvider.
  public async getLogoutRedirectUrl(req: express.Request, redirectUrl: URL): Promise<string> {
    if (process.env.GRIST_SAML_IDP_SKIP_SLO) {
      // TODO: This does NOT eventually take us to redirectUrl.
      return process.env.GRIST_SAML_IDP_LOGOUT!;
    }

    const sp = this._serviceProvider;
    const idp = this._identityProvider;

    // 2020: Not sure what I am doing wrong here, but all my attempt to use "Single Logout" fail with
    // a "400 Bad Request" error message from Okta.
    // 2021: This doesn't fail with Auth0 (now owned by Okta), but also doesn't seem to do anything.

    const { permit: relay_state, samlNameId, samlSessionIndex } = await this._prepareAppState(req, redirectUrl, {
      action: 'logout',
      waitMinutes: 1
    });

    const options: saml2.CreateLogoutRequestUrlOptions = {
      name_id: samlNameId,
      session_index: samlSessionIndex,
      relay_state,
    };
    return fromCallback<string>((cb) => sp.create_logout_request_url(idp, options, cb));
  }

  // Adds several /saml/* endpoints to the given express app, to support SAML logins.
  public addSamlEndpoints(app: express.Express, sessions: Sessions): void {
    const sp = this._serviceProvider;
    const idp = this._identityProvider;

    // A purely informational endpoint, which simply dumps the SAML metadata.
    app.get("/saml/metadata.xml", (req, res) => {
      res.type('application/xml');
      res.send(sp.create_metadata());
    });

    // Starting point for login. It redirects to the IdP, and then to /saml/assert.
    app.get("/saml/login", expressWrap(async (req, res, next) => {
      res.redirect(await this.getLoginRedirectUrl(req, new URL(getOriginUrl(req))));
    }));

    // Assert endpoint for when the login completes as POST.
    app.post("/saml/assert", express.urlencoded({extended: true}), expressWrap(async (req, res, next) => {
      const relayState: string = req.body.RelayState;
      if (!relayState) { throw new Error('Login or logout failed to complete'); }
      const permitStore = this._gristServer.getExternalPermitStore();
      const state = await permitStore.getPermit(relayState);
      if (!state) { throw new Error('Login or logout is stale'); }
      await permitStore.removePermit(relayState);

      const redirectUrl = state.url!;
      const samlResponse: any = await fromCallback((cb) => sp.post_assert(idp, {request_body: req.body}, cb));

      if (state.action === 'login') {
        const samlUser = samlResponse.user;
        if (!samlUser || !samlUser.name_id) {
          log.warn(`SamlConfig: bad SAML response: ${JSON.stringify(samlUser)}`);
          throw new Error("Invalid user info in SAML response");
        }

        // An example IdP response is at https://github.com/Clever/saml2#assert_response. Saml2-js
        // maps some standard attributes as user.given_name, user.surname, which we use if
        // available. Otherwise we use user.attributes which has the form {Name: [Value]}.
        const fname = samlUser.given_name || samlUser.attributes.FirstName || '';
        const lname = samlUser.surname || samlUser.attributes.LastName || '';
        const email = samlUser.email || samlUser.name_id;
        const profile = {
          email,
          name: `${fname} ${lname}`.trim(),
        };

        const samlSessionIndex = samlUser.session_index;
        const samlNameId = samlUser.name_id;
        log.info(`SamlConfig: got SAML response for ${profile.email} (${profile.name}) redirecting to ${redirectUrl}`);

        const scopedSession = sessions.getOrCreateSessionFromRequest(req, {sessionId: state.sessionId});
        await scopedSession.operateOnScopedSession(req, async (user) => Object.assign(user, {
          profile,
          samlSessionIndex,
          samlNameId,
        }));
      }
      res.redirect(redirectUrl);
    }));
  }

  /**
   *
   * Login and logout involves redirecting to a SAML IdP, which will then POST some information
   * back to Grist.  The POST won't have Grist's cookie, because of relatively new SameSite
   * behavior.  Grist's cookie is SameSite=Lax, which withholds cookies from POSTs initiated
   * on a different site.  That's a good setting in general, but for this case we need
   * to link what the identity provider sends us with the session.  We place some state
   * in the permit store temporarily and pass the permit key through the request chain
   * so it is available when needed.
   *
   */
  private async _prepareAppState(req: express.Request, redirectUrl: URL, options: {
    action: 'login' | 'logout',   // We'll need to remember whether we are logging in or out.
    waitMinutes: number        // State may need to linger quite some time for login,
                               // less so for logout.
  }) {
    const permitStore = this._gristServer.getExternalPermitStore();
    const sessionId = this._gristServer.getSessions().getSessionIdFromRequest(req);
    if (!sessionId) { throw new Error('no session available'); }
    const state: Permit = {
      url: redirectUrl.href,
      sessionId,
      action: options.action,
    };
    const scopedSession = this._gristServer.getSessions().getOrCreateSessionFromRequest(req);
    const userSession = await scopedSession.getScopedSession();
    const samlNameId = userSession.samlNameId;
    const samlSessionIndex = userSession.samlSessionIndex;
    const permit = await permitStore.setPermit(state, options.waitMinutes * 60 * 1000);
    return { permit, samlNameId, samlSessionIndex };
  }
}

/**
 * Return SAML login system if environment looks configured for it, else return undefined.
 */
export async function getSamlLoginSystem(): Promise<GristLoginSystem|undefined> {
  if (!process.env.GRIST_SAML_SP_HOST) {
    return undefined;
  }
  return {
    async getMiddleware(gristServer: GristServer) {
      const samlConfig = new SamlConfig(gristServer);
      await samlConfig.initSaml();
      return {
        getLoginRedirectUrl: samlConfig.getLoginRedirectUrl.bind(samlConfig),
        // For saml, always use regular login page, users are enrolled externally.
        // TODO: is there a better link to give here?
        getSignUpRedirectUrl: samlConfig.getLoginRedirectUrl.bind(samlConfig),
        getLogoutRedirectUrl: samlConfig.getLogoutRedirectUrl.bind(samlConfig),
        async addEndpoints(app: express.Express) {
          samlConfig.addSamlEndpoints(app, gristServer.getSessions());
          return 'saml';
        },
      };
    },
    deleteUser() {
      throw new Error('users cannot be deleted with SAML yet');
    },
  };
}