1 files changed, 110 insertions, 0 deletions
diff --git a/lib/byteback/disk_free_history.rb b/lib/byteback/disk_free_history.rb
new file mode 100755
index 0000000..ba66863
--- /dev/null
+++ b/lib/byteback/disk_free_history.rb
@@ -0,0 +1,110 @@
+#!/usr/bin/ruby
+
+require 'sys/filesystem'
+
+module Byteback
+	class DiskFreeReading < Struct.new(:fsstat, :time)
+		def initialize(fsstat,time=Time.now)
+			self.fsstat = fsstat
+			self.time = time
+		end
+
+		# helper method to return %age of disc space free
+		#
+		def percent_free
+			fsstat.blocks_available * 100 / fsstat.blocks
+		end
+	end
+
+	# A simple round-robin list  to store a short history of a given mount
+	# point's disk space history.
+	#
+	class DiskFreeHistory
+		MINIMUM_INTERVAL = 5*60 # don't take readings more than 5 mins apart
+		MAXIMUM_AGE = 7*24*60*60 # delete readings after a week
+
+		# Initialize a new list storing the disc space history for the given
+		# mount point.
+		#
+		def initialize(mountpoint, history_file=nil)
+			history_file = "#{mountpoint}/.disk_free_history" unless 
+			  history_file
+			@history_file = history_file
+			@mountpoint = mountpoint
+			load!
+		end
+
+		# Take a new reading
+		#
+		def new_reading!
+			reading = DiskFreeReading.new(Sys::Filesystem.stat(@mountpoint))
+
+			# Don't record a new reading if it's exactly the same as last time,
+			# and less than the minimum interval.
+			#
+			return nil if @list.last && 
+			  @list.last.fsstat.blocks_available == reading.fsstat.blocks_available
+			  Time.now - @list.last.time < MINIMUM_INTERVAL
+
+			@list << reading
+
+			save!
+		end
+
+		def list
+			load! unless @list
+			@list
+		end
+
+		def gradient(last_n_seconds, &value_from_reading)
+			value_from_reading ||= proc { |r| r.fsstat.blocks_available }
+			earliest = Time.now - last_n_seconds
+
+			total = 0
+			readings = 0
+			later_reading = nil
+
+			list.reverse.each do |reading|
+				if later_reading
+					difference = 
+						value_from_reading.call(reading) -
+						value_from_reading.call(later_reading)
+					total += difference
+					p difference
+				end
+				break if reading.time < earliest
+				readings += 1
+				later_reading = reading
+			end
+
+			total / readings
+		end
+
+		protected
+
+		def load!
+			begin
+				File.open(@history_file) do |fh|
+					@list = Marshal.restore(fh.read(1000000))
+				end
+			rescue Errno::ENOENT, TypeError => err
+				@list = []
+				new_reading!
+			end
+		end
+
+		def save!
+			list.shift while Time.now - list.first.time > MAXIMUM_AGE
+
+			tmp = "@history_file.#{$$}.#{rand(9999999999)}"
+			begin
+				File.open(tmp, "w") do |fh|
+					fh.write(Marshal.dump(list))
+					File.rename(tmp, @history_file)
+				end
+			ensure
+				File.unlink(tmp) if File.exists?(tmp)
+			end
+		end
+	end
+end