google_drive.rb

require 'google/api_client'
require 'google/api_client/auth/file_storage'
require 'google/api_client/auth/installed_app'

module Google
  class Drive
    # https://github.com/google/google-api-ruby-client-samples/blob/master/drive/drive.rb
    API_VERSION           = 'v2'.freeze
    CREDENTIAL_STORE_FILE = Rails.root.join('lib/google/credential_store.json').freeze

    def self.get_file(id:)
      result = client.execute(
        api_method: api_wrapper.files.get,
        parameters: { 'fileId' => id }
      )
      file = result.data
      download_url = file.exportLinks['text/csv']

      RestClient.get(download_url)
    end

    private

    def self.client
      @client ||= Google::APIClient.new(
        application_name: 'Wholesale Opt-in',
        application_version: '1.0.0'
      ).tap do |client_to_auth|
        file_storage = Google::APIClient::FileStorage.new(CREDENTIAL_STORE_FILE)
        if file_storage.authorization.nil?
          flow = Google::APIClient::InstalledAppFlow.new(
            client_id:     Figaro.env.google_client_id,
            client_secret: Figaro.env.google_client_secret,
            scope:         ['https://www.googleapis.com/auth/drive']
          )
          client_to_auth.authorization = flow.authorize(file_storage)
        else
          client_to_auth.authorization = file_storage.authorization
        end
      end
    end

    def self.api_wrapper
      @api_wrapper ||= client.discovered_api('drive', API_VERSION)
    end
  end
end