feat: unified watch server under org-garden

org-garden/lib/org_garden/watcher.ex

@@ -0,0 +1,236 @@
+defmodule OrgGarden.Watcher do
+  @moduledoc """
+  File-watching GenServer that detects `.org` file changes and triggers
+  incremental export + transform for only the affected files.
+
+  Uses the `file_system` package (inotify on Linux, fsevents on macOS)
+  to watch the notes directory. Events are debounced per-file (500ms)
+  to coalesce rapid writes (e.g., Emacs auto-save).
+
+  ## Lifecycle
+
+  Started dynamically by `OrgGarden.CLI` after the initial batch export.
+  Transforms are initialized once at startup and reused across all
+  incremental rebuilds to avoid repeated Zotero probes and BibTeX loads.
+
+  ## Usage
+
+      OrgGarden.Watcher.start_link(
+        notes_dir: "/path/to/notes",
+        output_dir: "/path/to/output",
+        content_dir: "/path/to/output/content",
+        pipeline_opts: %{zotero_url: "...", ...},
+        transforms: [OrgGarden.Transforms.Citations]
+      )
+  """
+
+  use GenServer
+
+  require Logger
+
+  @debounce_ms 500
+
+  # -------------------------------------------------------------------
+  # Client API
+  # -------------------------------------------------------------------
+
+  @doc """
+  Start the watcher as a linked process.
+
+  ## Options
+
+    * `:notes_dir`      — directory to watch for `.org` changes (required)
+    * `:output_dir`     — ox-hugo base dir (required)
+    * `:content_dir`    — directory where `.md` files are written (required)
+    * `:pipeline_opts`  — opts map passed to transforms (required)
+    * `:transforms`     — list of transform modules (default: `[OrgGarden.Transforms.Citations]`)
+  """
+  def start_link(opts) do
+    GenServer.start_link(__MODULE__, opts, name: __MODULE__)
+  end
+
+  # -------------------------------------------------------------------
+  # GenServer callbacks
+  # -------------------------------------------------------------------
+
+  @impl true
+  def init(opts) do
+    notes_dir = Keyword.fetch!(opts, :notes_dir)
+    output_dir = Keyword.fetch!(opts, :output_dir)
+    content_dir = Keyword.fetch!(opts, :content_dir)
+    pipeline_opts = Keyword.fetch!(opts, :pipeline_opts)
+    transforms = Keyword.get(opts, :transforms, [OrgGarden.Transforms.Citations])
+
+    # Initialize transforms once — reused for all incremental rebuilds
+    initialized_transforms = OrgGarden.init_transforms(transforms, pipeline_opts)
+
+    # Start the file system watcher
+    {:ok, watcher_pid} = FileSystem.start_link(dirs: [notes_dir], recursive: true)
+    FileSystem.subscribe(watcher_pid)
+
+    Logger.info("Watcher: monitoring #{notes_dir} for .org changes")
+
+    {:ok,
+     %{
+       notes_dir: notes_dir,
+       output_dir: output_dir,
+       content_dir: content_dir,
+       pipeline_opts: pipeline_opts,
+       watcher_pid: watcher_pid,
+       initialized_transforms: initialized_transforms,
+       pending: %{}
+     }}
+  end
+
+  @impl true
+  def handle_info({:file_event, _pid, {path, events}}, state) do
+    path = to_string(path)
+
+    if org_file?(path) and not temporary_file?(path) do
+      event_type = classify_events(events)
+      Logger.debug("Watcher: #{event_type} event for #{path}")
+      {:noreply, schedule_debounce(path, event_type, state)}
+    else
+      {:noreply, state}
+    end
+  end
+
+  @impl true
+  def handle_info({:file_event, _pid, :stop}, state) do
+    Logger.warning("Watcher: file system monitor stopped unexpectedly")
+    {:stop, :watcher_stopped, state}
+  end
+
+  @impl true
+  def handle_info({:debounced, path, event_type}, state) do
+    state = %{state | pending: Map.delete(state.pending, path)}
+
+    case event_type do
+      :deleted ->
+        handle_delete(path, state)
+
+      _created_or_modified ->
+        handle_change(path, state)
+    end
+
+    {:noreply, state}
+  end
+
+  @impl true
+  def terminate(_reason, state) do
+    OrgGarden.teardown_transforms(state.initialized_transforms)
+    :ok
+  end
+
+  # -------------------------------------------------------------------
+  # Event handling
+  # -------------------------------------------------------------------
+
+  defp handle_change(orgfile, state) do
+    %{
+      notes_dir: notes_dir,
+      output_dir: output_dir,
+      content_dir: content_dir,
+      pipeline_opts: pipeline_opts,
+      initialized_transforms: initialized_transforms
+    } = state
+
+    md_path = OrgGarden.Export.expected_md_path(orgfile, notes_dir, content_dir)
+    IO.puts("==> Changed: #{Path.relative_to(orgfile, notes_dir)}")
+
+    case OrgGarden.Export.export_file(orgfile, notes_dir, output_dir) do
+      {:ok, _} ->
+        IO.puts("  exported: #{Path.relative_to(md_path, content_dir)}")
+
+        {:ok, stats} = OrgGarden.run_on_files_with([md_path], initialized_transforms, pipeline_opts)
+
+        Enum.each(stats, fn {mod, count} ->
+          if count > 0, do: IO.puts("  #{inspect(mod)}: #{count} file(s) modified")
+        end)
+
+        regenerate_index(content_dir)
+        IO.puts("==> Done")
+
+      {:error, reason} ->
+        Logger.error("Watcher: export failed for #{orgfile}: #{inspect(reason)}")
+    end
+  end
+
+  defp handle_delete(orgfile, state) do
+    %{notes_dir: notes_dir, content_dir: content_dir} = state
+
+    md_path = OrgGarden.Export.expected_md_path(orgfile, notes_dir, content_dir)
+    IO.puts("==> Deleted: #{Path.relative_to(orgfile, notes_dir)}")
+
+    if File.exists?(md_path) do
+      File.rm!(md_path)
+      IO.puts("  removed: #{Path.relative_to(md_path, content_dir)}")
+
+      # Clean up empty parent directories left behind
+      cleanup_empty_dirs(Path.dirname(md_path), content_dir)
+    end
+
+    regenerate_index(content_dir)
+    IO.puts("==> Done")
+  end
+
+  # -------------------------------------------------------------------
+  # Index generation
+  # -------------------------------------------------------------------
+
+  defp regenerate_index(content_dir) do
+    OrgGarden.Index.regenerate(content_dir)
+  end
+
+  # -------------------------------------------------------------------
+  # Helpers
+  # -------------------------------------------------------------------
+
+  defp schedule_debounce(path, event_type, state) do
+    # Cancel any existing timer for this path
+    case Map.get(state.pending, path) do
+      nil -> :ok
+      old_ref -> Process.cancel_timer(old_ref)
+    end
+
+    ref = Process.send_after(self(), {:debounced, path, event_type}, @debounce_ms)
+    %{state | pending: Map.put(state.pending, path, ref)}
+  end
+
+  defp org_file?(path), do: String.ends_with?(path, ".org")
+
+  defp temporary_file?(path) do
+    basename = Path.basename(path)
+    # Emacs creates temp files like .#file.org and #file.org#
+    String.starts_with?(basename, ".#") or
+      (String.starts_with?(basename, "#") and String.ends_with?(basename, "#"))
+  end
+
+  defp classify_events(events) do
+    cond do
+      :removed in events or :deleted in events -> :deleted
+      :created in events -> :created
+      :modified in events or :changed in events -> :modified
+      # renamed can mean created or deleted depending on context;
+      # if the file exists it was renamed into the watched dir
+      :renamed in events -> :modified
+      true -> :modified
+    end
+  end
+
+  defp cleanup_empty_dirs(dir, stop_at) do
+    dir = Path.expand(dir)
+    stop_at = Path.expand(stop_at)
+
+    if dir != stop_at and File.dir?(dir) do
+      case File.ls!(dir) do
+        [] ->
+          File.rmdir!(dir)
+          cleanup_empty_dirs(Path.dirname(dir), stop_at)
+
+        _ ->
+          :ok
+      end
+    end
+  end
+end