// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License. See License.txt in the project root for license information.

import { MSITokenCredentials, MSIOptions, MSITokenResponse } from "./msiTokenCredentials";
import { RequestPrepareOptions, WebResource } from "@azure/ms-rest-js";

/**
 * Defines the optional parameters for authentication with MSI for AppService.
 */
export interface MSIAppServiceOptions extends MSIOptions {
  /**
   * The local URL from which your app can request tokens.
   * Unless this property is specified, any of the two environment variables `IDENTITY_ENDPOINT` or `MSI_ENDPOINT` will be used as the default value.
   */
  msiEndpoint?: string;
  /**
   * The secret used in communication between your code and the local MSI agent.
   * Unless this property is specified, any of the two environment variables `IDENTITY_SECRET` or `MSI_SECRET` will be used as the default value.
   */
  msiSecret?: string;
  /**
   * The api-version of the local MSI agent. Default value is "2017-09-01".
   */
  msiApiVersion?: string;
  /**
   * The clientId of the managed identity you would like the token for. Required, if
   * your app service has user-assigned managed identities.
   */
  clientId?: string;
}

/**
 * Provides information about managed service identity token credentials in an App Service environment.
 */
export class MSIAppServiceTokenCredentials extends MSITokenCredentials {
  /**
   * The local URL from which your app can request tokens.
   * Unless this property is specified, any of the two environment variables `IDENTITY_ENDPOINT` or `MSI_ENDPOINT` will be used as the default value.
   */
  msiEndpoint: string;
  /**
   * The secret used in communication between your code and the local MSI agent.
   * Unless this property is specified, any of the two environment variables `IDENTITY_SECRET` or `MSI_SECRET` will be used as the default value.
   */
  msiSecret: string;
  /**
   * The api-version of the local MSI agent. Default value is "2017-09-01".
   */
  msiApiVersion?: string;
  /**
   * The clientId of the managed identity you would like the token for. Required, if
   * your app service has user-assigned managed identities.
   */
  clientId?: string;

  /**
   * Creates an instance of MSIAppServiceTokenCredentials.
   * @param options.msiEndpoint - The local URL from which your app can request tokens.
   * Unless this property is specified, any of the two environment variables `IDENTITY_ENDPOINT` or `MSI_ENDPOINT` will be used as the default value.
   * @param options.msiSecret - The secret used in communication between your code and the local MSI agent.
   * Unless this property is specified, any of the two environment variables `IDENTITY_SECRET` or `MSI_SECRET` will be used as the default value.
   * @param options.resource - The resource uri or token audience for which the token is needed.
   * For e.g. it can be:
   * - resource management endpoint "https://management.azure.com/" (default)
   * - management endpoint "https://management.core.windows.net/"
   * @param options.msiApiVersion - The api-version of the local MSI agent. Default value is "2017-09-01".
   * @param options.clientId - The clientId of the managed identity you would like the token for. Required, if
   * your app service has user-assigned managed identities.
   */
  constructor(options?: MSIAppServiceOptions) {
    if (!options) options = {};
    super(options);
    options.msiEndpoint =
      options.msiEndpoint || process.env["IDENTITY_ENDPOINT"] || process.env["MSI_ENDPOINT"];
    options.msiSecret =
      options.msiSecret || process.env["IDENTITY_SECRET"] || process.env["MSI_SECRET"];
    if (
      !options.msiEndpoint ||
      (options.msiEndpoint && typeof options.msiEndpoint.valueOf() !== "string")
    ) {
      throw new Error(
        'Either provide "msiEndpoint" as a property of the "options" object ' +
          'or set the environment variable "IDENTITY_ENDPOINT" or "MSI_ENDPOINT" and it must be of type "string".'
      );
    }

    if (
      !options.msiSecret ||
      (options.msiSecret && typeof options.msiSecret.valueOf() !== "string")
    ) {
      throw new Error(
        'Either provide "msiSecret" as a property of the "options" object ' +
          'or set the environment variable "IDENTITY_SECRET" or "MSI_SECRET" and it must be of type "string".'
      );
    }

    if (!options.msiApiVersion) {
      options.msiApiVersion = "2017-09-01";
    } else if (typeof options.msiApiVersion.valueOf() !== "string") {
      throw new Error("msiApiVersion must be a uri.");
    }

    this.msiEndpoint = options.msiEndpoint;
    this.msiSecret = options.msiSecret;
    this.msiApiVersion = options.msiApiVersion;
    this.clientId = options.clientId;
  }

  /**
   * Prepares and sends a GET request to a service endpoint indicated by the app service, which responds with the access token.
   * @returns Promise with the tokenResponse (tokenType and accessToken are the two important properties).
   */
  async getToken(): Promise<MSITokenResponse> {
    const reqOptions = this.prepareRequestOptions();

    const opRes = await this._httpClient.sendRequest(reqOptions);
    if (opRes.bodyAsText === undefined || opRes.bodyAsText!.indexOf("ExceptionMessage") !== -1) {
      throw new Error(
        `MSI: Failed to retrieve a token from "${reqOptions.url}" with an error: ${opRes.bodyAsText}`
      );
    }

    const result = this.parseTokenResponse(opRes.bodyAsText!) as MSITokenResponse;
    if (!result.tokenType) {
      throw new Error(
        `Invalid token response, did not find tokenType. Response body is: ${opRes.bodyAsText}`
      );
    } else if (!result.accessToken) {
      throw new Error(
        `Invalid token response, did not find accessToken. Response body is: ${opRes.bodyAsText}`
      );
    }

    return result;
  }

  protected prepareRequestOptions(): WebResource {
    const endpoint = this.msiEndpoint.endsWith("/") ? this.msiEndpoint : `${this.msiEndpoint}/`;
    const reqOptions: RequestPrepareOptions = {
      url: endpoint,
      headers: {
        secret: this.msiSecret
      },
      queryParameters: {
        resource: this.resource,
        "api-version": this.msiApiVersion,
        clientid: this.clientId
      },
      method: "GET"
    };

    const webResource = new WebResource();
    return webResource.prepare(reqOptions);
  }
}