var AWS = require('./core');
require('./http');
var inherit = AWS.util.inherit;

/**
 * Represents a metadata service available on EC2 instances. Using the
 * {request} method, you can receieve metadata about any available resource
 * on the metadata service.
 *
 * You can disable the use of the IMDS by setting the AWS_EC2_METADATA_DISABLED
 * environment variable to a truthy value.
 *
 * @!attribute [r] httpOptions
 *   @return [map] a map of options to pass to the underlying HTTP request:
 *
 *     * **timeout** (Number) &mdash; a timeout value in milliseconds to wait
 *       before aborting the connection. Set to 0 for no timeout.
 *
 * @!macro nobrowser
 */
AWS.MetadataService = inherit({
  /**
   * @return [String] the hostname of the instance metadata service
   */
  host: '169.254.169.254',

  /**
   * @!ignore
   */

  /**
   * Default HTTP options. By default, the metadata service is set to not
   * timeout on long requests. This means that on non-EC2 machines, this
   * request will never return. If you are calling this operation from an
   * environment that may not always run on EC2, set a `timeout` value so
   * the SDK will abort the request after a given number of milliseconds.
   */
  httpOptions: { timeout: 0 },

  /**
   * when enabled, metadata service will not fetch token
   */
  disableFetchToken: false,

  /**
   * Creates a new MetadataService object with a given set of options.
   *
   * @option options host [String] the hostname of the instance metadata
   *   service
   * @option options httpOptions [map] a map of options to pass to the
   *   underlying HTTP request:
   *
   *   * **timeout** (Number) &mdash; a timeout value in milliseconds to wait
   *     before aborting the connection. Set to 0 for no timeout.
   * @option options maxRetries [Integer] the maximum number of retries to
   *   perform for timeout errors
   * @option options retryDelayOptions [map] A set of options to configure the
   *   retry delay on retryable errors. See AWS.Config for details.
   */
  constructor: function MetadataService(options) {
    AWS.util.update(this, options);
  },

  /**
   * Sends a request to the instance metadata service for a given resource.
   *
   * @param path [String] the path of the resource to get
   *
   * @param options [map] an optional map used to make request
   *
   *   * **method** (String) &mdash; HTTP request method
   *
   *   * **headers** (map<String,String>) &mdash; a map of response header keys and their respective values
   *
   * @callback callback function(err, data)
   *   Called when a response is available from the service.
   *   @param err [Error, null] if an error occurred, this value will be set
   *   @param data [String, null] if the request was successful, the body of
   *     the response
   */
  request: function request(path, options, callback) {
    if (arguments.length === 2) {
      callback = options;
      options = {};
    }

    if (process.env[AWS.util.imdsDisabledEnv]) {
      callback(new Error('EC2 Instance Metadata Service access disabled'));
      return;
    }

    path = path || '/';
    var httpRequest = new AWS.HttpRequest('http://' + this.host + path);
    httpRequest.method = options.method || 'GET';
    if (options.headers) {
      httpRequest.headers = options.headers;
    }
    AWS.util.handleRequestWithRetries(httpRequest, this, callback);
  },

  /**
  * @api private
  */
  loadCredentialsCallbacks: [],

  /**
   * Fetches metadata token used for getting credentials
   *
   * @api private
   * @callback callback function(err, token)
   *   Called when token is loaded from the resource
   */
  fetchMetadataToken: function fetchMetadataToken(callback) {
    var self = this;
    var tokenFetchPath = '/latest/api/token';
    self.request(
      tokenFetchPath,
      {
        'method': 'PUT',
        'headers': {
          'x-aws-ec2-metadata-token-ttl-seconds': '21600'
        }
      },
      callback
    );
  },

  /**
   * Fetches credentials
   *
   * @api private
   * @callback cb function(err, creds)
   *   Called when credentials are loaded from the resource
   */
  fetchCredentials: function fetchCredentials(options, cb) {
    var self = this;
    var basePath = '/latest/meta-data/iam/security-credentials/';

    self.request(basePath, options, function (err, roleName) {
      if (err) {
        self.disableFetchToken = !(err.statusCode === 401);
        cb(AWS.util.error(
          err,
          {
            message: 'EC2 Metadata roleName request returned error'
          }
        ));
        return;
      }
      roleName = roleName.split('\n')[0]; // grab first (and only) role
      self.request(basePath + roleName, options, function (credErr, credData) {
        if (credErr) {
          self.disableFetchToken = !(credErr.statusCode === 401);
          cb(AWS.util.error(
            credErr,
            {
              message: 'EC2 Metadata creds request returned error'
            }
          ));
          return;
        }
        try {
          var credentials = JSON.parse(credData);
          cb(null, credentials);
        } catch (parseError) {
          cb(parseError);
        }
      });
    });
  },

  /**
   * Loads a set of credentials stored in the instance metadata service
   *
   * @api private
   * @callback callback function(err, credentials)
   *   Called when credentials are loaded from the resource
   *   @param err [Error] if an error occurred, this value will be set
   *   @param credentials [Object] the raw JSON object containing all
   *     metadata from the credentials resource
   */
  loadCredentials: function loadCredentials(callback) {
    var self = this;
    self.loadCredentialsCallbacks.push(callback);
    if (self.loadCredentialsCallbacks.length > 1) { return; }

    function callbacks(err, creds) {
      var cb;
      while ((cb = self.loadCredentialsCallbacks.shift()) !== undefined) {
        cb(err, creds);
      }
    }

    if (self.disableFetchToken) {
      self.fetchCredentials({}, callbacks);
    } else {
      self.fetchMetadataToken(function(tokenError, token) {
        if (tokenError) {
          if (tokenError.code === 'TimeoutError') {
            self.disableFetchToken = true;
          } else if (tokenError.retryable === true) {
            callbacks(AWS.util.error(
              tokenError,
              {
                message: 'EC2 Metadata token request returned error'
              }
            ));
            return;
          } else if (tokenError.statusCode === 400) {
            callbacks(AWS.util.error(
              tokenError,
              {
                message: 'EC2 Metadata token request returned 400'
              }
            ));
            return;
          }
        }
        var options = {};
        if (token) {
          options.headers = {
            'x-aws-ec2-metadata-token': token
          };
        }
        self.fetchCredentials(options, callbacks);
      });

    }
  }
});

/**
 * @api private
 */
module.exports = AWS.MetadataService;
