Add LastFm feed for a given user

lib/last_fm/feed.ex

@@ -0,0 +1,24 @@
+defmodule LastFm.Feed do
+  @moduledoc """
+  Holds a in-memory cache of scrobbled tracks.
+
+  Tracks are keyed and ASC ordered by their scrobbling unix timestamp. While this
+  is technically prone to collision, it's very unlikely for that to happen due to the
+  nature of the data.
+  """
+  def create_table! do
+    __MODULE__ = :ets.new(__MODULE__, [:ordered_set, :named_table, :public])
+    :ok
+  end
+
+  def update(tracks) do
+    data = Enum.map(tracks, fn t -> {t.scrobbled_at_uts, t} end)
+
+    :ets.insert(__MODULE__, data)
+  end
+
+  def all do
+    :ets.tab2list(__MODULE__)
+    |> Enum.reverse()
+  end
+end