# Copyright 2013 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License 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 'json'
require 'signet/oauth_2/client'

module Google
  class APIClient
    ##
    # Represents cached OAuth 2 tokens stored on local disk in a
    # JSON serialized file. Meant to resemble the serialized format
    # http://google-api-python-client.googlecode.com/hg/docs/epy/oauth2client.file.Storage-class.html
    #
    class FileStorage
      # @return [String] Path to the credentials file.
      attr_reader :path

      # @return [Signet::OAuth2::Client] Path to the credentials file.
      attr_reader :authorization

      ##
      # Initializes the FileStorage object.
      #
      # @param [String] path
      #    Path to the credentials file.
      def initialize(path)
        self.path= path
        self.load_credentials
      end

      ##
      # Attempt to read in credentials from the specified file.
      def load_credentials
        cached_credentials = JSON.load(path)
        @authorization = Signet::OAuth2::Client.new(cached_credentials)
        @authorization.issued_at = Time.at(cached_credentials['issued_at'])
        self.refresh_authorization if @authorization.expired?
      end

      def path=(value)
        @path=value
        raise "Credentials on path #{path} not accessible" unless File.exists?(@path) && File.readable?(@path) && File.writable?(@path)
      end

      ##
      # refresh credentials and save them to file
      def refresh_authorization
        @authorization.refresh!
        self.write_credentials(@authorization)
      end

      ##
      # Write the credentials to the specified file.
      #
      # @param [Signet::OAuth2::Client] authorization
      #    Optional authorization instance. If not provided, the authorization
      #    already associated with this instance will be written.
      def write_credentials(authorization=nil)
        @authorization = authorization if authorization
        if @authorization.refresh_token

          credentials_hash = {
            :access_token          => @authorization.access_token,
            :authorization_uri     => @authorization.authorization_uri,
            :client_id             => @authorization.client_id,
            :client_secret         => @authorization.client_secret,
            :expires_in            => @authorization.expires_in,
            :refresh_token         => @authorization.refresh_token,
            :token_credential_uri  => @authorization.token_credential_uri
          }

          File.open(self.path, 'w', 0600) do |file|
            file.write(credentials_hash.to_json)
          end
        end
      end
    end
  end
end