/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

"use strict";

var EXPORTED_SYMBOLS = [
  "TokenServerClient",
  "TokenServerClientError",
  "TokenServerClientNetworkError",
  "TokenServerClientServerError",
];

const { Log } = ChromeUtils.importESModule(
  "resource://gre/modules/Log.sys.mjs"
);
const { RESTRequest } = ChromeUtils.import(
  "resource://services-common/rest.js"
);
const { Observers } = ChromeUtils.import(
  "resource://services-common/observers.js"
);

const PREF_LOG_LEVEL = "services.common.log.logger.tokenserverclient";

/**
 * Represents a TokenServerClient error that occurred on the client.
 *
 * This is the base type for all errors raised by client operations.
 *
 * @param message
 *        (string) Error message.
 */
function TokenServerClientError(message) {
  this.name = "TokenServerClientError";
  this.message = message || "Client error.";
  // Without explicitly setting .stack, all stacks from these errors will point
  // to the "new Error()" call a few lines down, which isn't helpful.
  this.stack = Error().stack;
}
TokenServerClientError.prototype = new Error();
TokenServerClientError.prototype.constructor = TokenServerClientError;
TokenServerClientError.prototype._toStringFields = function() {
  return { message: this.message };
};
TokenServerClientError.prototype.toString = function() {
  return this.name + "(" + JSON.stringify(this._toStringFields()) + ")";
};
TokenServerClientError.prototype.toJSON = function() {
  let result = this._toStringFields();
  result.name = this.name;
  return result;
};

/**
 * Represents a TokenServerClient error that occurred in the network layer.
 *
 * @param error
 *        The underlying error thrown by the network layer.
 */
function TokenServerClientNetworkError(error) {
  this.name = "TokenServerClientNetworkError";
  this.error = error;
  this.stack = Error().stack;
}
TokenServerClientNetworkError.prototype = new TokenServerClientError();
TokenServerClientNetworkError.prototype.constructor = TokenServerClientNetworkError;
TokenServerClientNetworkError.prototype._toStringFields = function() {
  return { error: this.error };
};

/**
 * Represents a TokenServerClient error that occurred on the server.
 *
 * This type will be encountered for all non-200 response codes from the
 * server. The type of error is strongly enumerated and is stored in the
 * `cause` property. This property can have the following string values:
 *
 *   invalid-credentials -- A token could not be obtained because
 *     the credentials presented by the client were invalid.
 *
 *   unknown-service -- The requested service was not found.
 *
 *   malformed-request -- The server rejected the request because it
 *     was invalid. If you see this, code in this file is likely wrong.
 *
 *   malformed-response -- The response from the server was not what was
 *     expected.
 *
 *   general -- A general server error has occurred. Clients should
 *     interpret this as an opaque failure.
 *
 * @param message
 *        (string) Error message.
 */
function TokenServerClientServerError(message, cause = "general") {
  this.now = new Date().toISOString(); // may be useful to diagnose time-skew issues.
  this.name = "TokenServerClientServerError";
  this.message = message || "Server error.";
  this.cause = cause;
  this.stack = Error().stack;
}
TokenServerClientServerError.prototype = new TokenServerClientError();
TokenServerClientServerError.prototype.constructor = TokenServerClientServerError;

TokenServerClientServerError.prototype._toStringFields = function() {
  let fields = {
    now: this.now,
    message: this.message,
    cause: this.cause,
  };
  if (this.response) {
    fields.response_body = this.response.body;
    fields.response_headers = this.response.headers;
    fields.response_status = this.response.status;
  }
  return fields;
};

/**
 * Represents a client to the Token Server.
 *
 * http://docs.services.mozilla.com/token/index.html
 *
 * The Token Server was designed to support obtaining tokens for arbitrary apps by
 * constructing URI paths of the form <app>/<app_version>. In practice this was
 * never used and it only supports an <app> value of `sync`, and the API presented
 * here reflects that.
 *
 * Areas to Improve:
 *
 *  - The server sends a JSON response on error. The client does not currently
 *    parse this. It might be convenient if it did.
 *  - Currently most non-200 status codes are rolled into one error type. It
 *    might be helpful if callers had a richer API that communicated who was
 *    at fault (e.g. differentiating a 503 from a 401).
 */
function TokenServerClient() {
  this._log = Log.repository.getLogger("Services.Common.TokenServerClient");
  this._log.manageLevelFromPref(PREF_LOG_LEVEL);
}
TokenServerClient.prototype = {
  /**
   * Logger instance.
   */
  _log: null,

  /**
   * Obtain a token from a provided OAuth token against a specific URL.
   *
   * This asynchronously obtains the token.
   * It returns a Promise that resolves or rejects:
   *
   *  Rejects with:
   *   (TokenServerClientError) If no token could be obtained, this
   *     will be a TokenServerClientError instance describing why. The
   *     type seen defines the type of error encountered. If an HTTP response
   *     was seen, a RESTResponse instance will be stored in the `response`
   *     property of this object. If there was no error and a token is
   *     available, this will be null.
   *
   *  Resolves with:
   *   (map) On success, this will be a map containing the results from
   *     the server. If there was an error, this will be null. The map has the
   *     following properties:
   *
   *       id       (string) HTTP MAC public key identifier.
   *       key      (string) HTTP MAC shared symmetric key.
   *       endpoint (string) URL where service can be connected to.
   *       uid      (string) user ID for requested service.
   *       duration (string) the validity duration of the issued token.
   *
   * Example Usage
   * -------------
   *
   *   let client = new TokenServerClient();
   *   let access_token = getOAuthAccessTokenFromSomewhere();
   *   let url = "https://token.services.mozilla.com/1.0/sync/2.0";
   *
   *   try {
   *     const result = await client.getTokenUsingOAuth(url, access_token);
   *     let {id, key, uid, endpoint, duration} = result;
   *     // Do stuff with data and carry on.
   *   } catch (error) {
   *     // Handle errors.
   *   }
   * Obtain a token from a provided OAuth token against a specific URL.
   *
   * @param  url
   *         (string) URL to fetch token from.
   * @param  oauthToken
   *         (string) FxA OAuth Token to exchange token for.
   * @param  addHeaders
   *         (object) Extra headers for the request.
   */
  async getTokenUsingOAuth(url, oauthToken, addHeaders = {}) {
    this._log.debug("Beginning OAuth token exchange: " + url);

    if (!oauthToken) {
      throw new TokenServerClientError("oauthToken argument is not valid.");
    }

    return this._tokenServerExchangeRequest(
      url,
      `Bearer ${oauthToken}`,
      addHeaders
    );
  },

  /**
   * Performs the exchange request to the token server to
   * produce a token based on the authorizationHeader input.
   *
   * @param  url
   *         (string) URL to fetch token from.
   * @param  authorizationHeader
   *         (string) The auth header string that populates the 'Authorization' header.
   * @param  addHeaders
   *         (object) Extra headers for the request.
   */
  async _tokenServerExchangeRequest(url, authorizationHeader, addHeaders = {}) {
    if (!url) {
      throw new TokenServerClientError("url argument is not valid.");
    }

    if (!authorizationHeader) {
      throw new TokenServerClientError(
        "authorizationHeader argument is not valid."
      );
    }

    let req = this.newRESTRequest(url);
    req.setHeader("Accept", "application/json");
    req.setHeader("Authorization", authorizationHeader);

    for (let header in addHeaders) {
      req.setHeader(header, addHeaders[header]);
    }
    let response;
    try {
      response = await req.get();
    } catch (err) {
      throw new TokenServerClientNetworkError(err);
    }

    try {
      return this._processTokenResponse(response);
    } catch (ex) {
      if (ex instanceof TokenServerClientServerError) {
        throw ex;
      }
      this._log.warn("Error processing token server response", ex);
      let error = new TokenServerClientError(ex);
      error.response = response;
      throw error;
    }
  },

  /**
   * Handler to process token request responses.
   *
   * @param response
   *        RESTResponse from token HTTP request.
   */
  _processTokenResponse(response) {
    this._log.debug("Got token response: " + response.status);

    // Responses should *always* be JSON, even in the case of 4xx and 5xx
    // errors. If we don't see JSON, the server is likely very unhappy.
    let ct = response.headers["content-type"] || "";
    if (ct != "application/json" && !ct.startsWith("application/json;")) {
      this._log.warn("Did not receive JSON response. Misconfigured server?");
      this._log.debug("Content-Type: " + ct);
      this._log.debug("Body: " + response.body);

      let error = new TokenServerClientServerError(
        "Non-JSON response.",
        "malformed-response"
      );
      error.response = response;
      throw error;
    }

    let result;
    try {
      result = JSON.parse(response.body);
    } catch (ex) {
      this._log.warn("Invalid JSON returned by server: " + response.body);
      let error = new TokenServerClientServerError(
        "Malformed JSON.",
        "malformed-response"
      );
      error.response = response;
      throw error;
    }

    // Any response status can have X-Backoff or X-Weave-Backoff headers.
    this._maybeNotifyBackoff(response, "x-weave-backoff");
    this._maybeNotifyBackoff(response, "x-backoff");

    // The service shouldn't have any 3xx, so we don't need to handle those.
    if (response.status != 200) {
      // We /should/ have a Cornice error report in the JSON. We log that to
      // help with debugging.
      if ("errors" in result) {
        // This could throw, but this entire function is wrapped in a try. If
        // the server is sending something not an array of objects, it has
        // failed to keep its contract with us and there is little we can do.
        for (let error of result.errors) {
          this._log.info("Server-reported error: " + JSON.stringify(error));
        }
      }

      let error = new TokenServerClientServerError();
      error.response = response;

      if (response.status == 400) {
        error.message = "Malformed request.";
        error.cause = "malformed-request";
      } else if (response.status == 401) {
        // Cause can be invalid-credentials, invalid-timestamp, or
        // invalid-generation.
        error.message = "Authentication failed.";
        error.cause = result.status;
      } else if (response.status == 404) {
        error.message = "Unknown service.";
        error.cause = "unknown-service";
      }

      // A Retry-After header should theoretically only appear on a 503, but
      // we'll look for it on any error response.
      this._maybeNotifyBackoff(response, "retry-after");

      throw error;
    }

    for (let k of ["id", "key", "api_endpoint", "uid", "duration"]) {
      if (!(k in result)) {
        let error = new TokenServerClientServerError(
          "Expected key not present in result: " + k
        );
        error.cause = "malformed-response";
        error.response = response;
        throw error;
      }
    }

    this._log.debug("Successful token response");
    return {
      id: result.id,
      key: result.key,
      endpoint: result.api_endpoint,
      uid: result.uid,
      duration: result.duration,
      hashed_fxa_uid: result.hashed_fxa_uid,
      node_type: result.node_type,
    };
  },

  /*
   * The prefix used for all notifications sent by this module.  This
   * allows the handler of notifications to be sure they are handling
   * notifications for the service they expect.
   *
   * If not set, no notifications will be sent.
   */
  observerPrefix: null,

  // Given an optional header value, notify that a backoff has been requested.
  _maybeNotifyBackoff(response, headerName) {
    if (!this.observerPrefix) {
      return;
    }
    let headerVal = response.headers[headerName];
    if (!headerVal) {
      return;
    }
    let backoffInterval;
    try {
      backoffInterval = parseInt(headerVal, 10);
    } catch (ex) {
      this._log.error(
        "TokenServer response had invalid backoff value in '" +
          headerName +
          "' header: " +
          headerVal
      );
      return;
    }
    Observers.notify(
      this.observerPrefix + ":backoff:interval",
      backoffInterval
    );
  },

  // override points for testing.
  newRESTRequest(url) {
    return new RESTRequest(url);
  },
};