Extracted from qwan-tracker

lib/microprint_cache.ex

@@ -0,0 +1,103 @@
+defmodule Microprints.MicroprintCache do
+  @moduledoc """
+  GenServer that caches microprint visualizations in ETS.
+
+  Subscribes to a PubSub topic and invalidates cache entries when files
+  change via LiveReload (or any other file watcher).
+
+  ## Configuration
+
+  The PubSub module and topic can be configured via `Application` environment:
+
+      config :microprints,
+        pubsub: MyApp.PubSub,
+        pubsub_topic: "dev_tools_files"
+
+  Defaults to `Phoenix.PubSub` and `"dev_tools_files"`.
+  """
+
+  use GenServer
+
+  alias Microprints.Microprint
+
+  @table_name :microprint_cache
+  @live_reload_topic "dev_tools_files"
+
+  # Client API
+
+  @doc """
+  Starts the MicroprintCache GenServer.
+
+  ## Options
+
+  * `:pubsub` - The PubSub module to use (defaults to `Phoenix.PubSub`)
+  * `:pubsub_topic` - The PubSub topic to subscribe to (defaults to `"dev_tools_files"`)
+  """
+  def start_link(opts \\ []) do
+    pubsub = opts[:pubsub] || Application.get_env(:microprints, :pubsub, Phoenix.PubSub)
+    pubsub_topic = opts[:pubsub_topic] || Application.get_env(:microprints, :pubsub_topic, @live_reload_topic)
+
+    GenServer.start_link(__MODULE__, %{pubsub: pubsub, pubsub_topic: pubsub_topic}, name: __MODULE__)
+  end
+
+  @doc """
+  Returns the microprint for the given file path.
+
+  Returns cached version if available, otherwise generates and caches it.
+  """
+  @spec get_microprint(String.t()) :: {:ok, Microprint.microprint()} | {:error, term()}
+  def get_microprint(path) do
+    absolute_path = Path.expand(path)
+
+    case :ets.lookup(@table_name, absolute_path) do
+      [{^absolute_path, microprint}] ->
+        {:ok, microprint}
+
+      [] ->
+        case Microprint.generate(absolute_path) do
+          {:ok, microprint} ->
+            :ets.insert(@table_name, {absolute_path, microprint})
+            {:ok, microprint}
+
+          error ->
+            error
+        end
+    end
+  end
+
+  @doc """
+  Invalidates the cache entry for the given path.
+  """
+  @spec invalidate(String.t()) :: true
+  def invalidate(path) do
+    absolute_path = Path.expand(path)
+    :ets.delete(@table_name, absolute_path)
+  end
+
+  @doc """
+  Clears all cached microprints.
+  """
+  @spec clear_all() :: true
+  def clear_all do
+    :ets.delete_all_objects(@table_name)
+  end
+
+  # Server callbacks
+
+  @impl true
+  def init(%{pubsub: pubsub, pubsub_topic: pubsub_topic}) do
+    table = :ets.new(@table_name, [:named_table, :public, :set, read_concurrency: true])
+    Phoenix.PubSub.subscribe(pubsub, pubsub_topic)
+    {:ok, %{table: table, pubsub_topic: pubsub_topic}}
+  end
+
+  @impl true
+  def handle_info({:phoenix_live_reload, _topic, path}, state) do
+    invalidate(path)
+    {:noreply, state}
+  end
+
+  def handle_info(_msg, state) do
+    {:noreply, state}
+  end
+end