init

lib/forum/forms/watcher.ex

@@ -0,0 +1,108 @@
+defmodule Forum.Forms.Watcher do
+  @moduledoc """
+  Watches the canonical forms.html file and reloads `Forum.Forms` when it changes.
+
+  This intentionally uses a small polling loop instead of an external file watcher
+  dependency so it works the same way in dev, test, and releases.
+  """
+  use GenServer
+  require Logger
+
+  @poll_ms 500
+  @debounce_ms 200
+
+  def start_link(opts) do
+    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+  end
+
+  @impl true
+  def init(_opts) do
+    paths = paths()
+    state = %{paths: paths, signature: signature(paths), debounce_ref: nil}
+
+    schedule_poll()
+    {:ok, state}
+  end
+
+  @impl true
+  def handle_info(:poll, state) do
+    paths = paths()
+    next_signature = signature(paths)
+    state = %{state | paths: paths}
+
+    state =
+      if next_signature != state.signature do
+        schedule_reload(%{state | signature: next_signature})
+      else
+        state
+      end
+
+    schedule_poll()
+    {:noreply, state}
+  end
+
+  def handle_info({:reload, signature}, %{signature: signature} = state) do
+    case reload_forms() do
+      :ok ->
+        Logger.info("Forum.Forms.Watcher: reloaded #{Enum.join(state.paths, ", ")}")
+        broadcast_reload()
+
+      {:error, reason} ->
+        Logger.error("Forum.Forms.Watcher: reload failed: #{inspect(reason)}")
+    end
+
+    {:noreply, %{state | debounce_ref: nil}}
+  end
+
+  def handle_info({:reload, _stale_signature}, state) do
+    {:noreply, state}
+  end
+
+  defp schedule_reload(%{debounce_ref: ref} = state) when is_reference(ref) do
+    Process.cancel_timer(ref)
+    schedule_reload(%{state | debounce_ref: nil})
+  end
+
+  defp schedule_reload(state) do
+    ref = Process.send_after(self(), {:reload, state.signature}, @debounce_ms)
+    %{state | debounce_ref: ref}
+  end
+
+  defp schedule_poll do
+    Process.send_after(self(), :poll, @poll_ms)
+  end
+
+  defp paths do
+    [Forum.Forms.path() | Enum.map(Forum.Forms.network_paths(), fn {_slug, path} -> path end)]
+  end
+
+  defp signature(paths) do
+    Enum.map(paths, fn path ->
+      case File.read(path) do
+        {:ok, raw} -> {path, :ok, :erlang.phash2(raw), byte_size(raw)}
+        {:error, reason} -> {path, :error, reason}
+      end
+    end)
+  end
+
+  defp reload_forms do
+    try do
+      Forum.Forms.reload()
+    rescue
+      error -> {:error, error}
+    catch
+      kind, reason -> {:error, {kind, reason}}
+    else
+      :ok -> :ok
+      other -> {:error, other}
+    end
+  end
+
+  defp broadcast_reload do
+    html = Forum.Forms.html()
+
+    for {pid, _value} <- Registry.lookup(Forum.FormsSubscriberRegistry, :forms) do
+      send(pid, {:forms_reloaded, html})
+    end
+  end
+end