Fix modified_at comparisons to use seconds granularity

lib/code_corps/validators/time_validator.ex

@@ -7,20 +7,32 @@ defmodule CodeCorps.Validators.TimeValidator do
 
   @doc """
   Validates the new time is not before the previous time.
+
+  Works at second-level accuracy by truncating both timestamps to the second.
   """
   def validate_time_not_before(%{data: data} = changeset, field) do
     previous_time = Map.get(data, field)
-    current_time = Changeset.get_change(changeset, field)
-    case current_time do
+    new_time = Changeset.get_change(changeset, field)
+    case new_time do
       nil -> changeset
-      _ -> do_validate_time_not_before(changeset, field, previous_time, current_time)
+      _ -> do_validate_time_not_before(changeset, field, previous_time, new_time)
     end
   end
 
-  defp do_validate_time_not_before(changeset, field, previous_time, current_time) do
-    case Timex.before?(current_time, previous_time) do
+  defp do_validate_time_not_before(changeset, field, previous_time, new_time) do
+    previous_time = previous_time |> truncate(:second)
+    new_time = new_time |> truncate(:second)
+    case Timex.before?(new_time, previous_time) do
       true -> Changeset.add_error(changeset, field, "cannot be before the last recorded time")
       false -> changeset
     end
   end
+
+  # TODO: Replace this with DateTime.truncate/2 when Elixir 1.6 releases
+  @spec truncate(DateTime.t, :microsecond | :millisecond | :second) :: DateTime.t
+  def truncate(%DateTime{microsecond: microsecond} = datetime, precision) do
+    %{datetime | microsecond: do_truncate(microsecond, precision)}
+  end
+
+  defp do_truncate(_, :second), do: {0, 0}
 end

test/lib/code_corps/validators/time_validator_test.exs

@@ -8,32 +8,40 @@ defmodule CodeCorps.Validators.TimeValidatorTest do
   describe "validate_time_not_before/2" do
     test "when the time happened before" do
       # set the time to 1 day before the previous (recorded) time
-      current_time = @previous_time |> Timex.shift(days: -1)
-      changeset = cast_times(@previous_time, current_time, :modified_at)
+      new_time = @previous_time |> Timex.shift(days: -1)
+      changeset = cast_times(@previous_time, new_time, :modified_at)
       changeset = changeset |> validate_time_not_before(:modified_at)
       refute changeset.valid?
     end
 
     test "when the time happened at the same time" do
-      current_time = @previous_time
-      changeset = cast_times(@previous_time, current_time, :modified_at)
+      new_time = @previous_time
+      changeset = cast_times(@previous_time, new_time, :modified_at)
+      changeset = changeset |> validate_time_not_before(:modified_at)
+      assert changeset.valid?
+    end
+
+    test "when the time happened at the same second but with microseconds of difference" do
+      previous_time = @previous_time |> Timex.shift(milliseconds: 500)
+      new_time = previous_time |> truncate(:second)
+      changeset = cast_times(previous_time, new_time, :modified_at)
       changeset = changeset |> validate_time_not_before(:modified_at)
       assert changeset.valid?
     end
 
     test "when the time happened after" do
       # set the time to 1 day after the previous (recorded) time
-      current_time = @previous_time |> Timex.shift(days: 1)
-      changeset = cast_times(@previous_time, current_time, :modified_at)
+      new_time = @previous_time |> Timex.shift(days: 1)
+      changeset = cast_times(@previous_time, new_time, :modified_at)
       changeset = changeset |> validate_time_not_before(:modified_at)
       assert changeset.valid?
     end
   end
 
-  defp cast_times(previous_time, current_time, field) do
+  defp cast_times(previous_time, new_time, field) do
     data = Map.put(%{}, field, previous_time)
     fields = Map.put(%{}, field, :utc_datetime)
-    params = Map.put(%{}, field, current_time)
+    params = Map.put(%{}, field, new_time)
     Ecto.Changeset.cast({data, fields}, params, [field])
   end
 end