Add the ability to "rollup" values in a time series (#554)

* Clean up time series models

* Add value group rollup class for summarizing hierarchical data

* Integrate new classes

* Update UI to use new patterns

* Update D3 charts to expect new data format

* Clean up account model

* More cleanup

* Money improvements

* Use new money fields

* Remove invalid fixture data to avoid orphaned accountables

* Update time series to work better with collections

* Fix tests and UI bugs

app/models/value_group.rb

@@ -0,0 +1,100 @@
+  class ValueGroup
+    attr_accessor :parent
+    attr_reader :name, :children, :value, :original
+
+    def initialize(name = "Root", value: nil, original: nil)
+        @name = name
+        @value = value
+        @children = []
+        @original = original
+    end
+
+    def sum
+        return value if is_value_node?
+        return 0 if children.empty? && value.nil?
+        children.sum(&:sum)
+    end
+
+    def avg
+        return value if is_value_node?
+        return 0 if children.empty? && value.nil?
+        leaf_values = value_nodes.map(&:value)
+        leaf_values.compact.sum.to_f / leaf_values.compact.size
+    end
+
+    def series
+        return @raw_series || TimeSeries.new([]) if is_value_node?
+        summed_by_date = children.each_with_object(Hash.new(0)) do |child, acc|
+            child.series.values.each do |series_value|
+                acc[series_value.date] += series_value.value
+            end
+        end
+
+        summed_series = summed_by_date.map { |date, value| { date: date, value: value } }
+        TimeSeries.new(summed_series)
+    end
+
+    def value_nodes
+        return [ self ] unless value.nil?
+        children.flat_map { |child| child.value_nodes }
+    end
+
+    def percent_of_total
+        return 100 if parent.nil?
+        ((sum / parent.sum) * 100).round(1)
+    end
+
+    def leaf?
+        children.empty?
+    end
+
+    def add_child_node(name)
+        raise "Cannot add subgroup to node with a value" if is_value_node?
+        child = self.class.new(name)
+        child.parent = self
+        @children << child
+        child
+    end
+
+    def add_value_node(obj)
+        raise "Cannot add value node to a non-leaf node" unless can_add_value_node?
+        child = create_value_node(obj)
+        child.parent = self
+        @children << child
+        child
+    end
+
+    def attach_series(raw_series)
+        validate_attached_series(raw_series)
+        @raw_series = raw_series
+    end
+
+    def is_value_node?
+        value.present?
+    end
+
+    private
+        def can_add_value_node?
+            return false if is_value_node?
+            children.empty? || children.all?(&:is_value_node?)
+        end
+
+        def create_value_node(obj)
+            value = if obj.respond_to?(:value)
+                obj.value
+            elsif obj.respond_to?(:balance)
+                obj.balance
+            elsif obj.respond_to?(:amount)
+                obj.amount
+            else
+                raise ArgumentError, "Object must have a value, balance, or amount"
+            end
+
+            self.class.new(obj.name, value: value, original: obj)
+        end
+
+        def validate_attached_series(series)
+            raise "Cannot add series to a node without a value" unless is_value_node?
+            raise "Attached series must be a TimeSeries" unless series.is_a?(TimeSeries)
+        end
+  end