christhekeele · December 13, 2017 19:54 · Dec 13, 2017 · Dec 13, 2017 · Dec 13, 2017 · Dec 13, 2017
diff --git a/mnemonix-passthrough-proxy.ex b/mnemonix-passthrough-proxy.ex
@@ -17,19 +17,34 @@ defmodule Mnemonix.Stores.Meta.PassThrough do
       "bar"
       iex> Mnemonix.get(frontend, "foo")
       "bar"
+      
       iex> Mnemonix.put(passthrough, "foo", "baz")
       iex> Mnemonix.get(frontend, "foo")
       "baz"
       iex> Mnemonix.get(backend, "foo")
       "baz"
+      
       iex> Mnemonix.delete(passthrough, "foo")
       iex> Mnemonix.get(frontend, "foo")
       nil
       iex> Mnemonix.get(backend, "foo")
       nil
+      
       iex> {nil, ^passthrough} = Mnemonix.get_and_update(passthrough, "foo", &({&1, {&1, &1}}))
       iex> Mnemonix.get(passthrough, "foo")
       {nil, nil}
+      
+      iex> Mnemonix.Stores.Meta.PassThrough.__info__(:functions) |> IO.inspect(limit: :infinity)
+      #=> [bump: 3, bump!: 3, child_spec: 0, child_spec: 1, collectable_into: 2,
+      #=>  decrement: 2, decrement: 3, delete: 2, deserialize_key: 2,
+      #=>  deserialize_value: 2, do_bump: 4, do_bump_calculation: 3, drop: 2,
+      #=>  enumerable?: 1, enumerable_count: 1, enumerable_member?: 2,
+      #=>  enumerable_reduce: 3, fetch: 2, fetch!: 2, get: 2, get: 3, get_and_update: 3,
+      #=>  get_and_update!: 3, get_lazy: 3, has_key?: 2, increment: 2, increment: 3,
+      #=>  keys: 1, msg_for: 2, pop: 2, pop: 3, pop_lazy: 3, put: 3, put_new: 3,
+      #=>  put_new_lazy: 3, replace: 3, replace!: 3, serialize_key: 2, serialize_value: 2,
+      #=>  setup: 1, setup_initial: 1, split: 2, start_link: 0, start_link: 1, take: 2,
+      #=>  teardown: 2, to_enumerable: 1, to_list: 1, update: 4, update!: 3, values: 1]
 
   This store raises errors on the functions in `Mnemonix.Features.Enumerable`.
   """

diff --git a/mnemonix-passthrough-proxy.ex b/mnemonix-passthrough-proxy.ex
@@ -27,6 +27,9 @@ defmodule Mnemonix.Stores.Meta.PassThrough do
       nil
       iex> Mnemonix.get(backend, "foo")
       nil
+      iex> {nil, ^passthrough} = Mnemonix.get_and_update(passthrough, "foo", &({&1, {&1, &1}}))
+      iex> Mnemonix.get(passthrough, "foo")
+      {nil, nil}
 
   This store raises errors on the functions in `Mnemonix.Features.Enumerable`.
   """

diff --git a/mnemonix-passthrough-proxy.ex b/mnemonix-passthrough-proxy.ex
@@ -17,6 +17,16 @@ defmodule Mnemonix.Stores.Meta.PassThrough do
       "bar"
       iex> Mnemonix.get(frontend, "foo")
       "bar"
+      iex> Mnemonix.put(passthrough, "foo", "baz")
+      iex> Mnemonix.get(frontend, "foo")
+      "baz"
+      iex> Mnemonix.get(backend, "foo")
+      "baz"
+      iex> Mnemonix.delete(passthrough, "foo")
+      iex> Mnemonix.get(frontend, "foo")
+      nil
+      iex> Mnemonix.get(backend, "foo")
+      nil
 
   This store raises errors on the functions in `Mnemonix.Features.Enumerable`.
   """

diff --git a/mnemonix-passthrough-proxy.ex b/mnemonix-passthrough-proxy.ex
@@ -0,0 +1,89 @@
+defmodule Mnemonix.Stores.Meta.PassThrough do
+  @moduledoc """
+  A `Mnemonix.Store` that caches reads from a backend store into a frontend one.
+
+  Writes and removals are applied to both stores.
+
+  Works best with quicker or closer stores in the frontend, like in-memory ones;
+  with a store-wide ttl to keep their footprint light.
+
+      iex> {:ok, backend} = Mnemonix.Stores.Redix.start_link()
+      iex> {:ok, frontend} = Mnemonix.Stores.ETS.start_link()
+      iex> {:ok, passthrough} = Mnemonix.Stores.Meta.PassThrough.start_link(frontend: frontend, backend: backend)
+      iex> Mnemonix.put(backend, "foo", "bar")
+      iex> Mnemonix.get(frontend, "foo")
+      nil
+      iex> Mnemonix.get(passthrough, "foo")
+      "bar"
+      iex> Mnemonix.get(frontend, "foo")
+      "bar"
+
+  This store raises errors on the functions in `Mnemonix.Features.Enumerable`.
+  """
+
+  alias Mnemonix.Store
+
+  use Store.Behaviour
+  use Store.Translator.Raw
+
+  ####
+  # Mnemonix.Store.Behaviours.Core
+  ##
+
+  @doc """
+  Tracks frontend and backend stores furnished in `opts`.
+
+  ## Options
+
+  - `frontend:` A store reference to cache reads from the backend store in.
+  - `backend:` A store reference to use as the canonical uncached source of truth.
+  """
+  @impl Store.Behaviours.Core
+  @spec setup(Store.options()) :: {:ok, state :: term} | {:stop, reason :: any}
+  def setup(opts) do
+    {:ok, %{frontend: Keyword.fetch!(opts, :frontend), backend: Keyword.fetch!(opts, :backend)}}
+  end
+
+  ####
+  # Mnemonix.Store.Behaviours.Map
+  ##
+
+  @impl Store.Behaviours.Map
+  @spec delete(Store.t(), Mnemonix.key()) :: Store.Server.instruction()
+  def delete(%Store{state: state} = store, key) do
+    %{frontend: frontend, backend: backend} = state
+    with ^frontend <- Mnemonix.delete(frontend, key),
+         ^backend <- Mnemonix.delete(backend, key) do
+      {:ok, store}
+    end
+  end
+
+  @impl Store.Behaviours.Map
+  @spec fetch(Store.t(), Mnemonix.key()) ::
+          Store.Server.instruction({:ok, Mnemonix.value()} | :error)
+  def fetch(%Store{state: state} = store, key) do
+    %{frontend: frontend, backend: backend} = state
+    if value = Mnemonix.get(frontend, key) do
+      {:ok, store, {:ok, value}}
+    else
+      if value = Mnemonix.get(backend, key) do
+        with ^frontend <- Mnemonix.put(frontend, key, value) do
+          {:ok, store, {:ok, value}}
+        end
+      else
+        {:ok, store, :error}
+      end
+    end
+  end
+
+  @impl Store.Behaviours.Map
+  @spec put(Store.t(), Mnemonix.key(), Mnemonix.value()) :: Store.Server.instruction()
+  def put(%Store{state: state} = store, key, value) do
+    %{frontend: frontend, backend: backend} = state
+    with ^frontend <- Mnemonix.put(frontend, key, value),
+         ^backend <- Mnemonix.put(backend, key, value) do
+      {:ok, store}
+    end
+  end
+
+end
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