subtree(users/wpcarro): docking briefcase at '24f5a642'

git-subtree-dir: users/wpcarro
git-subtree-mainline: 464bbcb15c
git-subtree-split: 24f5a642af
Change-Id: I6105b3762b79126b3488359c95978cadb3efa789

users/wpcarro/assessments/semiprimes/server/lib/cache.ex

@@ -0,0 +1,41 @@
+defmodule Cache do
+  @moduledoc """
+  Cache is an in-memory key-value store.
+  """
+  use Agent
+
+  @doc """
+  Inititalize the key-value store.
+  """
+  def start_link(_) do
+    Agent.start_link(fn -> %{} end, name: __MODULE__)
+  end
+
+  @doc """
+  Attempt to return the value stored at `key`
+  """
+  def get(key) do
+    Agent.get(__MODULE__, &Map.get(&1, key))
+  end
+
+  @doc """
+  Write the `value` under the `key`. Last writer wins.
+  """
+  def put(key, value) do
+    Agent.update(__MODULE__, &Map.put(&1, key, value))
+  end
+
+  @doc """
+  List the contents of the cache. Useful for debugging purposes.
+  """
+  def list() do
+    Agent.get(__MODULE__, & &1)
+  end
+
+  @doc """
+  Invalidate the entire cache.
+  """
+  def clear() do
+    Agent.update(__MODULE__, fn _ -> %{} end)
+  end
+end