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require 'googleauth/signet'
require 'googleauth/credentials_loader'
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://www.googleapis.com/oauth2/v3/token'
      extend CredentialsLoader

      # 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|
          fail "the json is missing the #{key} field" unless json_key.key?(key)
        end
        json_key
      end

      # Initializes 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 initialize(options = {})
        json_key_io, scope = options.values_at(:json_key_io, :scope)
        user_creds = self.class.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]
        }

        super(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
    end
  end
end