# Copyright 2015, Google Inc.
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#
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# notice, this list of conditions and the following disclaimer.
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# in the documentation and/or other materials provided with the
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require 'googleauth/signet'
require 'googleauth/credentials_loader'
require 'googleauth/scope_util'
require 'multi_json'

module Google
  # Module Auth provides classes that provide Google-specific authorization
  # used to access Google APIs.
  module Auth
    # Authenticates requests using User Refresh credentials.
    #
    # This class allows authorizing requests from user refresh tokens.
    #
    # This the end of the result of a 3LO flow.  E.g, the end result of
    # 'gcloud auth login' saves a file with these contents in well known
    # location
    #
    # cf [Application Default Credentials](http://goo.gl/mkAHpZ)
    class UserRefreshCredentials < Signet::OAuth2::Client
      TOKEN_CRED_URI = 'https://oauth2.googleapis.com/token'.freeze
      AUTHORIZATION_URI = 'https://accounts.google.com/o/oauth2/auth'.freeze
      REVOKE_TOKEN_URI = 'https://oauth2.googleapis.com/revoke'.freeze
      extend CredentialsLoader

      # Create a UserRefreshCredentials.
      #
      # @param json_key_io [IO] an IO from which the JSON key can be read
      # @param scope [string|array|nil] the scope(s) to access
      def self.make_creds(options = {})
        json_key_io, scope = options.values_at(:json_key_io, :scope)
        user_creds = read_json_key(json_key_io) if json_key_io
        user_creds ||= {
          'client_id'     => ENV[CredentialsLoader::CLIENT_ID_VAR],
          'client_secret' => ENV[CredentialsLoader::CLIENT_SECRET_VAR],
          'refresh_token' => ENV[CredentialsLoader::REFRESH_TOKEN_VAR]
        }

        new(token_credential_uri: TOKEN_CRED_URI,
            client_id: user_creds['client_id'],
            client_secret: user_creds['client_secret'],
            refresh_token: user_creds['refresh_token'],
            scope: scope)
      end

      # Reads the client_id, client_secret and refresh_token fields from the
      # JSON key.
      def self.read_json_key(json_key_io)
        json_key = MultiJson.load(json_key_io.read)
        wanted = %w(client_id client_secret refresh_token)
        wanted.each do |key|
          raise "the json is missing the #{key} field" unless json_key.key?(key)
        end
        json_key
      end

      def initialize(options = {})
        options ||= {}
        options[:token_credential_uri] ||= TOKEN_CRED_URI
        options[:authorization_uri] ||= AUTHORIZATION_URI
        super(options)
      end

      # Revokes the credential
      def revoke!(options = {})
        c = options[:connection] || Faraday.default_connection

        retry_with_error do
          resp = c.post(REVOKE_TOKEN_URI, token: refresh_token || access_token)
          case resp.status
          when 200
            self.access_token = nil
            self.refresh_token = nil
            self.expires_at = 0
          else
            raise(Signet::AuthorizationError,
                  "Unexpected error code #{resp.status}")
          end
        end
      end

      # Verifies that a credential grants the requested scope
      #
      # @param [Array<String>, String] required_scope
      #  Scope to verify
      # @return [Boolean]
      #  True if scope is granted
      def includes_scope?(required_scope)
        missing_scope = Google::Auth::ScopeUtil.normalize(required_scope) -
                        Google::Auth::ScopeUtil.normalize(scope)
        missing_scope.empty?
      end
    end
  end
end