# Copyright 2015, Google Inc.
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
#     * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following disclaimer
# in the documentation and/or other materials provided with the
# distribution.
#     * Neither the name of Google Inc. nor the names of its
# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

require 'memoist'
require 'os'
require 'rbconfig'

module Google
  # Module Auth provides classes that provide Google-specific authorization
  # used to access Google APIs.
  module Auth
    # CredentialsLoader contains the behaviour used to locate and find default
    # credentials files on the file system.
    module CredentialsLoader
      extend Memoist
      ENV_VAR = 'GOOGLE_APPLICATION_CREDENTIALS'.freeze

      PRIVATE_KEY_VAR = 'GOOGLE_PRIVATE_KEY'.freeze
      CLIENT_EMAIL_VAR = 'GOOGLE_CLIENT_EMAIL'.freeze
      CLIENT_ID_VAR = 'GOOGLE_CLIENT_ID'.freeze
      CLIENT_SECRET_VAR = 'GOOGLE_CLIENT_SECRET'.freeze
      REFRESH_TOKEN_VAR = 'GOOGLE_REFRESH_TOKEN'.freeze
      ACCOUNT_TYPE_VAR = 'GOOGLE_ACCOUNT_TYPE'.freeze

      CREDENTIALS_FILE_NAME = 'application_default_credentials.json'.freeze
      NOT_FOUND_ERROR =
        "Unable to read the credential file specified by #{ENV_VAR}".freeze
      WELL_KNOWN_PATH = "gcloud/#{CREDENTIALS_FILE_NAME}".freeze
      WELL_KNOWN_ERROR = 'Unable to read the default credential file'.freeze

      SYSTEM_DEFAULT_ERROR =
        'Unable to read the system default credential file'.freeze

      CLOUD_SDK_CLIENT_ID = '764086051850-6qr4p6gpi6hn506pt8ejuq83di341hur.app'\
        's.googleusercontent.com'.freeze

      CLOUD_SDK_CREDENTIALS_WARNING = 'Your application has authenticated '\
        'using end user credentials from Google Cloud SDK. We recommend that '\
        'most server applications use service accounts instead. If your '\
        'application continues to use end user credentials from Cloud SDK, '\
        'you might receive a "quota exceeded" or "API not enabled" error. For'\
        ' more information about service accounts, see '\
        'https://cloud.google.com/docs/authentication/.'.freeze

      # make_creds proxies the construction of a credentials instance
      #
      # By default, it calls #new on the current class, but this behaviour can
      # be modified, allowing different instances to be created.
      def make_creds(*args)
        new(*args)
      end

      # Creates an instance from the path specified in an environment
      # variable.
      #
      # @param scope [string|array|nil] the scope(s) to access
      def from_env(scope = nil)
        if ENV.key?(ENV_VAR)
          path = ENV[ENV_VAR]
          raise "file #{path} does not exist" unless File.exist?(path)
          File.open(path) do |f|
            return make_creds(json_key_io: f, scope: scope)
          end
        elsif service_account_env_vars? || authorized_user_env_vars?
          return make_creds(scope: scope)
        end
      rescue StandardError => e
        raise "#{NOT_FOUND_ERROR}: #{e}"
      end

      # Creates an instance from a well known path.
      #
      # @param scope [string|array|nil] the scope(s) to access
      def from_well_known_path(scope = nil)
        home_var = OS.windows? ? 'APPDATA' : 'HOME'
        base = WELL_KNOWN_PATH
        root = ENV[home_var].nil? ? '' : ENV[home_var]
        base = File.join('.config', base) unless OS.windows?
        path = File.join(root, base)
        return nil unless File.exist?(path)
        File.open(path) do |f|
          return make_creds(json_key_io: f, scope: scope)
        end
      rescue StandardError => e
        raise "#{WELL_KNOWN_ERROR}: #{e}"
      end

      # Creates an instance from the system default path
      #
      # @param scope [string|array|nil] the scope(s) to access
      def from_system_default_path(scope = nil)
        if OS.windows?
          return nil unless ENV['ProgramData']
          prefix = File.join(ENV['ProgramData'], 'Google/Auth')
        else
          prefix = '/etc/google/auth/'
        end
        path = File.join(prefix, CREDENTIALS_FILE_NAME)
        return nil unless File.exist?(path)
        File.open(path) do |f|
          return make_creds(json_key_io: f, scope: scope)
        end
      rescue StandardError => e
        raise "#{SYSTEM_DEFAULT_ERROR}: #{e}"
      end

      # Issues warning if cloud sdk client id is used
      def warn_if_cloud_sdk_credentials(client_id)
        warn CLOUD_SDK_CREDENTIALS_WARNING if client_id == CLOUD_SDK_CLIENT_ID
      end

      private

      def service_account_env_vars?
        ([PRIVATE_KEY_VAR, CLIENT_EMAIL_VAR] - ENV.keys).empty?
      end

      def authorized_user_env_vars?
        ([CLIENT_ID_VAR, CLIENT_SECRET_VAR, REFRESH_TOKEN_VAR] -
          ENV.keys).empty?
      end
    end
  end
end