defmodule Pandoc.Watcher do
  @moduledoc false

  use GenServer

  def start_link(args) do
    GenServer.start_link(__MODULE__, args)
  end

  # Callbacks

  @impl true
  def init([profile, options, pattern, extra_args]) do
    {:ok, watcher_pid} = FileSystem.start_link(options)
    FileSystem.subscribe(watcher_pid)
    {:ok, %{watcher_pid: watcher_pid, profile: profile, pattern: pattern, extra_args: extra_args}}
  end

  @impl true
  def handle_info({:file_event, watcher_pid, {path, events}}, %{watcher_pid: watcher_pid} = state) do
    case {String.match?(path, state[:pattern]), :closed in events or :deleted in events} do
      {true, true} ->
        Pandoc.install_and_run(state[:profile], [Path.basename(path) | state[:extra_args]])

      _ ->
        nil
    end

    {:noreply, state}
  end

  def handle_info({:file_event, watcher_pid, :stop}, %{watcher_pid: watcher_pid} = state) do
    {:noreply, state}
  end
end