# Copyright 2015, Google Inc.
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#
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# modification, are permitted provided that the following conditions are
# met:
#
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# notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above
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# in the documentation and/or other materials provided with the
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# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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require 'multi_json'
require 'stringio'

require 'googleauth/credentials_loader'
require 'googleauth/service_account'
require 'googleauth/user_refresh'

module Google
  # Module Auth provides classes that provide Google-specific authorization
  # used to access Google APIs.
  module Auth
    # DefaultCredentials is used to preload the credentials file, to determine
    # which type of credentials should be loaded.
    class DefaultCredentials
      extend CredentialsLoader

      # override CredentialsLoader#make_creds to use the class determined by
      # loading the json.
      def self.make_creds(options = {})
        json_key_io, scope = options.values_at(:json_key_io, :scope)
        if json_key_io
          json_key, clz = determine_creds_class(json_key_io)
          clz.make_creds(json_key_io: StringIO.new(MultiJson.dump(json_key)),
                         scope: scope)
        else
          clz = read_creds
          clz.make_creds(scope: scope)
        end
      end

      def self.read_creds
        env_var = CredentialsLoader::ACCOUNT_TYPE_VAR
        type = ENV[env_var]
        raise "#{env_var} is undefined in env" unless type
        case type
        when 'service_account'
          ServiceAccountCredentials
        when 'authorized_user'
          UserRefreshCredentials
        else
          raise "credentials type '#{type}' is not supported"
        end
      end

      # Reads the input json and determines which creds class to use.
      def self.determine_creds_class(json_key_io)
        json_key = MultiJson.load(json_key_io.read)
        key = 'type'
        raise "the json is missing the '#{key}' field" unless json_key.key?(key)
        type = json_key[key]
        case type
        when 'service_account'
          [json_key, ServiceAccountCredentials]
        when 'authorized_user'
          [json_key, UserRefreshCredentials]
        else
          raise "credentials type '#{type}' is not supported"
        end
      end
    end
  end
end