Extract tracker into supervision tree.

lib/elixir_koans.ex

@@ -6,7 +6,8 @@ defmodule ElixirKoans do
     import Supervisor.Spec
 
     children = [
-      worker(Display, [])
+      worker(Display, []),
+      worker(Tracker, [])
     ]
 
     opts = [strategy: :one_for_one, name: ElixirKoans.Supervisor]

lib/meditate.ex

@@ -17,11 +17,13 @@ defmodule Mix.Tasks.Meditate do
       Display.disable_clear()
     end
 
-    Options.initial_koan
+    modules = Options.initial_koan
     |> ok?
     |> Runner.modules_to_run
-    |> Tracker.start
-    |> Runner.run
+
+    Tracker.set_total(modules)
+
+    Runner.run(modules)
 
     if Tracker.complete? do
       Display.congratulate

lib/tracker.ex

@@ -1,22 +1,27 @@
 defmodule Tracker do
-  def start(modules) do
+  alias __MODULE__
+
+  defstruct total: 0, koans: MapSet.new(), visited_modules: MapSet.new()
+
+  def start_link do
+    Agent.start_link(fn -> %Tracker{} end, name: __MODULE__)
+  end
+
+  def set_total(modules) do
     total = modules
     |> Enum.flat_map(&(&1.all_koans))
     |> Enum.count
 
-    Agent.start_link(fn -> %{total: total,
-                             koans: MapSet.new(),
-                             visited_modules: MapSet.new()} end, name: __MODULE__)
-    modules
+    Agent.update(__MODULE__, fn _ -> %Tracker{total: total} end)
   end
 
-  defp get(),  do: Agent.get(__MODULE__, &(&1))
-
   def completed(module, koan) do
-    Agent.update(__MODULE__, fn(%{koans: completed, visited_modules: modules} = all) ->
-      %{ all | koans: MapSet.put(completed, koan),
-               visited_modules: MapSet.put(modules, module)}
-    end)
+    Agent.update(__MODULE__, &mark_koan_completed(&1, module, koan))
+  end
+
+  defp mark_koan_completed(state, module, koan) do
+    %{state | koans: MapSet.put(state.koans, koan),
+       visited_modules: MapSet.put(state.visited_modules, module)}
   end
 
   def visited do
@@ -28,14 +33,13 @@ defmodule Tracker do
     total == completed
   end
 
-  def summarize, do: get() |> summarize()
-  defp summarize(%{total: total,
-                  koans: completed,
-                  visited_modules: modules}) do
+  def summarize do
+    state = Agent.get(__MODULE__, &(&1))
+
     %{
-      total: total,
-      current: MapSet.size(completed),
-      visited_modules: MapSet.to_list(modules)
+      total: state.total,
+      current: MapSet.size(state.koans),
+      visited_modules: MapSet.to_list(state.visited_modules)
     }
   end
 end

test/tracker_test.exs

@@ -4,25 +4,25 @@ defmodule TrackerTest do
   @sample_modules [SampleKoan, PassingKoan]
 
   test "can start" do
-    Tracker.start(@sample_modules)
+    Tracker.set_total(@sample_modules)
     assert Tracker.summarize == %{total: 2, current: 0, visited_modules: []}
   end
 
   test "can be notified of completed koans" do
-    Tracker.start(@sample_modules)
+    Tracker.set_total(@sample_modules)
     Tracker.completed(SampleKoan, :"Hi there")
     assert Tracker.summarize == %{total: 2, current: 1, visited_modules: [SampleKoan]}
   end
 
   test "multiple comletions of the same koan count only once" do
-    Tracker.start(@sample_modules)
+    Tracker.set_total(@sample_modules)
     Tracker.completed(SampleKoan, :"Hi there")
     Tracker.completed(SampleKoan, :"Hi there")
     assert Tracker.summarize == %{total: 2, current: 1, visited_modules: [SampleKoan]}
   end
 
   test "knows when koans are not complete" do
-    Tracker.start(@sample_modules)
+    Tracker.set_total(@sample_modules)
     refute Tracker.complete?
   end
 end