fix sparkline inserting zeroes where none should be

lib/dagon/listens/sparkline.ex

@@ -6,12 +6,8 @@ defmodule Dagon.Listens.Sparkline do
     beginning_interval = get_duration(oldest_listen.listened_at, date_first)
     end_interval = get_duration(date_last, newest_listen.listened_at)
 
-    filled_listens =
-      listens_per_month
-      |> fill_gaps()
-
     fill_list(beginning_interval) ++
-      filled_listens ++
+      fill_gaps(listens_per_month) ++
       fill_list(end_interval)
   end
 
@@ -27,7 +23,16 @@ defmodule Dagon.Listens.Sparkline do
     end
   end
 
-  defp fill_gaps(listens) do
+  def stupid_diff(from, until) do
+    from = Timex.to_date(from)
+    until = Timex.to_date(until)
+
+    (until.month - from.month) + (year_diff(from, until) * 12)
+  end
+
+  def year_diff(from, until), do: until.year - from.year
+  
+  def fill_gaps(listens) do
     new_list =
       for {[count, listen], index} <- Enum.with_index(listens) do
         case Enum.at(listens, index + 1) do
@@ -36,8 +41,8 @@ defmodule Dagon.Listens.Sparkline do
 
           [_, next_listen] ->
             duration =
-              Timex.Interval.new(from: listen, until: next_listen)
-              |> Timex.Interval.duration(:months)
+              (stupid_diff(listen, next_listen) - 1)
+              |> IO.inspect()
               |> fill_list()
 
             [count] ++ duration

test/dagon/listens/sparkline_test.exs

@@ -0,0 +1,24 @@
+defmodule Dagon.Listens.SparklineTest do
+  use Dagon.DataCase
+
+	alias Dagon.Listens.Sparkline
+
+  @august ~D[2008-08-31]
+  @september ~D[2008-09-30]
+  @october ~D[2008-10-31]
+  @december ~D[2008-12-31]
+  @january ~D[2009-01-31]
+
+  describe "sparkline" do
+    test "stupid_diff correctly diffs months" do
+      assert Sparkline.stupid_diff(@august, @september) == 1
+      assert Sparkline.stupid_diff(@august, @october) == 2
+      assert Sparkline.stupid_diff(@december, @january) == 1
+
+    end
+
+    test "year_diff correctly diffs years" do
+      assert Sparkline.year_diff(@august, @september) == 0
+    end
+  end
+end