# Copyright 2011 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You
# may not use this file except in compliance with the License. A copy of
# the License is located at
#
#     http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file is
# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
# ANY KIND, either express or implied. See the License for the specific
# language governing permissions and limitations under the License.

require 'base64'
require 'openssl'

module AWS

  # Computes signatures using credentials that are stored in memory.
  class DefaultSigner

    # @return [String] The Access Key ID used to sign requests.
    attr_reader :access_key_id

    # @return [String] The Secret Access Key used to sign requests.
    attr_reader :secret_access_key

    # @return [String] The Session Token used to sign requests.
    attr_reader :session_token

    # @param [String] access_key_id The Access Key ID used to sign
    #   requests.
    #
    # @param [String] secret_access_key The Secret Access Key used to
    #   sign requests.
    #
    # @param [String] session_token The Session Token used to sign
    #   requests.  You can get credentials that include a session
    #   token using the {STS} class.
    def initialize(access_key_id,
                   secret_access_key,
                   session_token = nil)
      @access_key_id = access_key_id
      @secret_access_key = secret_access_key
      @session_token = session_token
    end

    # Signs a string using the credentials stored in memory.
    #
    # @param [String] string_to_sign The string to sign.
    #
    # @param [String] digest_method The digest method to use when
    #   computing the HMAC digest.
    def sign(string_to_sign, digest_method = 'sha256')
      Base64.encode64(
        OpenSSL::HMAC.digest(
          OpenSSL::Digest::Digest.new(digest_method),
          secret_access_key, 
          string_to_sign)).strip
    end

  end
end
