require "dropbox_sdk"

module Backup
  module Storage
    class Dropbox < Base
      include Storage::Cycler
      class Error < Backup::Error; end

      ##
      # Dropbox API credentials
      attr_accessor :api_key, :api_secret

      ##
      # Path to store cached authorized session.
      #
      # Relative paths will be expanded using Config.root_path,
      # which by default is ~/Backup unless --root-path was used
      # on the command line or set in config.rb.
      #
      # By default, +cache_path+ is '.cache', which would be
      # '~/Backup/.cache/' if using the default root_path.
      attr_accessor :cache_path

      ##
      # Dropbox Access Type
      # Valid values are:
      #   :app_folder (default)
      #   :dropbox (full access)
      attr_accessor :access_type

      ##
      # Chunk size, specified in MiB, for the ChunkedUploader.
      attr_accessor :chunk_size

      ##
      # Number of times to retry failed operations.
      #
      # Default: 10
      attr_accessor :max_retries

      ##
      # Time in seconds to pause before each retry.
      #
      # Default: 30
      attr_accessor :retry_waitsec

      ##
      # Creates a new instance of the storage object
      def initialize(model, storage_id = nil)
        super

        @path           ||= "backups"
        @cache_path     ||= ".cache"
        @access_type    ||= :app_folder
        @chunk_size     ||= 4 # MiB
        @max_retries    ||= 10
        @retry_waitsec  ||= 30
        path.sub!(/^\//, "")
      end

      private

      ##
      # The initial connection to Dropbox will provide the user with an
      # authorization url. The user must open this URL and confirm that the
      # authorization successfully took place. If this is the case, then the
      # user hits 'enter' and the session will be properly established.
      # Immediately after establishing the session, the session will be
      # serialized and written to a cache file in +cache_path+.
      # The cached file will be used from that point on to re-establish a
      # connection with Dropbox at a later time. This allows the user to avoid
      # having to go to a new Dropbox URL to authorize over and over again.
      def connection
        return @connection if @connection

        unless session = cached_session
          Logger.info "Creating a new session!"
          session = create_write_and_return_new_session!
        end

        # will raise an error if session not authorized
        @connection = DropboxClient.new(session, access_type)

      rescue => err
        raise Error.wrap(err, "Authorization Failed")
      end

      ##
      # Attempt to load a cached session
      def cached_session
        session = false
        if File.exist?(cached_file)
          begin
            session = DropboxSession.deserialize(File.read(cached_file))
            Logger.info "Session data loaded from cache!"

          rescue => err
            Logger.warn Error.wrap(err, <<-EOS)
              Could not read session data from cache.
              Cache data might be corrupt.
            EOS
          end
        end
        session
      end

      ##
      # Transfer each of the package files to Dropbox in chunks of +chunk_size+.
      # Each chunk will be retried +chunk_retries+ times, pausing +retry_waitsec+
      # between retries, if errors occur.
      def transfer!
        package.filenames.each do |filename|
          src = File.join(Config.tmp_path, filename)
          dest = File.join(remote_path, filename)
          Logger.info "Storing '#{dest}'..."

          uploader = nil
          File.open(src, "r") do |file|
            uploader = connection.get_chunked_uploader(file, file.stat.size)
            while uploader.offset < uploader.total_size
              with_retries do
                uploader.upload(1024**2 * chunk_size)
              end
            end
          end

          with_retries do
            uploader.finish(dest)
          end
        end

      rescue => err
        raise Error.wrap(err, "Upload Failed!")
      end

      def with_retries
        retries = 0
        begin
          yield
        rescue StandardError => err
          retries += 1
          raise if retries > max_retries

          Logger.info Error.wrap(err, "Retry ##{retries} of #{max_retries}.")
          sleep(retry_waitsec)
          retry
        end
      end

      # Called by the Cycler.
      # Any error raised will be logged as a warning.
      def remove!(package)
        Logger.info "Removing backup package dated #{package.time}..."

        connection.file_delete(remote_path_for(package))
      end

      def cached_file
        path = cache_path.start_with?("/") ?
               cache_path : File.join(Config.root_path, cache_path)
        File.join(path, api_key + api_secret)
      end

      ##
      # Serializes and writes the Dropbox session to a cache file
      def write_cache!(session)
        FileUtils.mkdir_p File.dirname(cached_file)
        File.open(cached_file, "w") do |cache_file|
          cache_file.write(session.serialize)
        end
      end

      ##
      # Create a new session, write a serialized version of it to the
      # .cache directory, and return the session object
      def create_write_and_return_new_session!
        require "timeout"

        session = DropboxSession.new(api_key, api_secret)

        # grab the request token for session
        session.get_request_token

        template = Backup::Template.new(
          session: session, cached_file: cached_file
        )
        template.render("storage/dropbox/authorization_url.erb")

        # wait for user to hit 'return' to continue
        Timeout.timeout(180) { STDIN.gets }

        # this will raise an error if the user did not
        # visit the authorization_url and grant access
        #
        # get the access token from the server
        # this will be stored with the session in the cache file
        session.get_access_token

        template.render("storage/dropbox/authorized.erb")
        write_cache!(session)
        template.render("storage/dropbox/cache_file_written.erb")

        session

      rescue => err
        raise Error.wrap(err, "Could not create or authenticate a new session")
      end
    end
  end
end