Accumulator mods

lib/gruff/accumulator_bar.rb

@@ -4,15 +4,47 @@
 # A special bar graph that shows a single dataset as a set of
 # stacked bars. The bottom bar shows the running total and 
 # the top bar shows the new value being added to the array.
+#
+# An optional "Carry Forward" value can be set which will initialize the
+# accumulator to a non-zero value. If a label is provided for the carry_forward,
+# then a band of data (mostly zero's) will be plugged in as the middle data set
+# and there will be an actual visible representation of the carry-forward.
+# Without a label, the graph will show the accumulator starting at a non-zero point.
 
 class Gruff::AccumulatorBar < Gruff::StackedBar
+  attr_accessor :accumulator_label
+  attr_accessor :carry_forward
+  attr_accessor :carry_forward_label
+
+  def initialize(*)
+    super
+    @accumulator_label = 'Accumulator'
+  end
+
   def draw
     raise(Gruff::IncorrectNumberOfDatasetsException) unless @data.length == 1
 
-    accum_array = @data.first[DATA_VALUES_INDEX][0..-2].inject([0]) { |a, v| a << a.last + v}
-    data 'Accumulator', accum_array
+    accum_array = @data.first[DATA_VALUES_INDEX][0..-2].inject([carry_forward.nil? ? 0 : carry_forward]) { |a, v| a << a.last + v}
+
+    # Insert a data row for the carry-forward if explicitly given a label for it (and a value!)
+    if ! carry_forward.nil? && ! carry_forward_label.nil?
+      carry_array = Array.new(accum_array.length, 0)
+      # Since we'll be representing the carry-forward,
+      # remove it's value from the first bar of the accumulator.
+      accum_array[0] -= carry_forward
+      carry_array[0] += carry_forward
+    end
+
+    data accumulator_label, accum_array
+    data carry_forward_label, carry_array if ! carry_forward.nil? && ! carry_forward_label.nil?
+
     set_colors
-    @data.reverse!
+
+    # Swap in a way that's friendly to the optional carry-forward row.
+    accum_array = @data[-1]
+    @data[-1] = @data[0]
+    @data[0] = accum_array
+
     super
   end
 end