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/time_series.rb

@@ -0,0 +1,83 @@
+
+class TimeSeries
+    attr_reader :type
+
+    def self.from_collection(collection, value_method, options = {})
+        data = collection.map do |obj|
+            { date: obj.date, value: obj.public_send(value_method), original: obj }
+        end
+        new(data, options)
+    end
+
+    def initialize(data, options = {})
+        @type = options[:type] || :normal
+        initialize_series_data(data)
+    end
+
+    def values
+        @values ||= add_trends_to_series
+    end
+
+    def first
+        values.first
+    end
+
+    def last
+        values.last
+    end
+
+    def on(date)
+        values.find { |v| v.date == date }
+    end
+
+    def trend
+        TimeSeries::Trend.new(
+            current: last&.value,
+            previous: first&.value,
+            type: @type
+        )
+    end
+
+    # Data shape that frontend expects for D3 charts
+    def to_json(*_args)
+        {
+            values: values.map do |v|
+                {
+                    date: v.date,
+                    value: JSON.parse(v.value.to_json),
+                    trend: {
+                        type: v.trend.type,
+                        direction: v.trend.direction,
+                        value: JSON.parse(v.trend.value.to_json),
+                        percent: v.trend.percent
+                    }
+                }
+            end,
+            trend: {
+                type: @type,
+                direction: trend.direction,
+                value: JSON.parse(trend.value.to_json),
+                percent: trend.percent
+            },
+            type: @type
+        }.to_json
+    end
+
+    private
+        def initialize_series_data(data)
+            @series_data = data.nil? || data.empty? ? [] : data.map { |d| TimeSeries::Value.new(d) }.sort_by(&:date)
+        end
+
+        def add_trends_to_series
+            [ nil, *@series_data ].each_cons(2).map do |previous, current|
+                unless current.trend
+                    current.trend = TimeSeries::Trend.new(
+                        current: current.value,
+                        previous: previous&.value,
+                        type: @type
+                    )
+                end
+                current
+            end
+        end
+end