deferred class
	EL_NOTIFYING_FILE

inherit
	FILE
		redefine
			close, move, go, recede, back, start, finish, forth
		end

	EL_SHARED_DATA_TRANSFER_PROGRESS_LISTENER

feature -- Basic operations

	notify_final
		do
			notify_progress (True)
		end

	notify
		do
			notify_progress (False)
		end

	close
		do
			notify_final
			Precursor
		end

feature -- Cursor movement

	back
		do
			Precursor
			last_position := position
		end

	start
		do
			Precursor
			last_position := position
		end

	finish
		do
			Precursor
			last_position := position
		end

	forth
			-- Go to next position.
		do
			Precursor
			last_position := position
		end

	go (abs_position: INTEGER)
		do
			notify_final
			Precursor (abs_position)
			last_position := position
		end

	move (offset: INTEGER)
		do
			notify_final
			Precursor (offset)
			last_position := position
		end

	recede (abs_position: INTEGER)
		do
			notify_final
			Precursor (abs_position)
			last_position := position
		end

feature {NONE} -- Implementation

	notify_progress (final: BOOLEAN)
		-- notify progress of file operation
		local
			delta_count: INTEGER
		do
			delta_count := position - last_position
			if not final implies delta_count > 500 then
				progress_listener.on_notify (delta_count)
				last_position := position
			end
		end

	last_position: INTEGER

end