persist document to database after 2 seconds of no updates, initialize with current state when joining genserver

lib/poex/pads/document.ex

@@ -9,7 +9,7 @@ defmodule Poex.Pads.Document do
   @primary_key {:id, Ecto.UUID, autogenerate: true}
   schema "pad_documents" do
     field :title, :string
-    field :state, :map, default: %{ops: []}
+    field :contents, {:array, :map}, default: []
     has_many :operations, Poex.Pads.Operation
 
     timestamps(type: :utc_datetime)
@@ -18,7 +18,7 @@ defmodule Poex.Pads.Document do
   @doc false
   def changeset(document, attrs) do
     document
-    |> cast(attrs, [:title, :state])
+    |> cast(attrs, [:title, :contents])
     |> cast_assoc(:operations)
   end
 end

lib/poex/pads/document_server.ex

@@ -1,8 +1,11 @@
 defmodule Poex.Pads.DocumentServer do
   use GenServer
+  alias Poex.Pads.Document
+  alias Poex.Pads
   alias Poex.Utils.DeltaUtils
 
   @initial_state %{
+    save_scheduled: false,
     # Number of changes made to the document so far
     version: 0,
 
@@ -36,7 +39,8 @@ defmodule Poex.Pads.DocumentServer do
   def init(args) do
     id = args.id
     Registry.register(Poex.Pads.DocumentRegistry, id, [])
-    initial_state = Map.put(@initial_state, :id, id)
+    %Document{contents: current_state} = Pads.get_pad_document(id)
+    initial_state = Map.put(@initial_state, :id, id) |> Map.put(:contents, current_state)
     {:ok, initial_state}
   end
 
@@ -50,19 +54,28 @@ defmodule Poex.Pads.DocumentServer do
     change = DeltaUtils.convert_ops(change_map)
     inverted = Delta.invert(change, state.contents)
 
-    state = %{
+    save_scheduled =
+      if state.save_scheduled do
+        true
+      else
+        Process.send_after(self(), :save, 2000)
+        true
+      end
+
+    new_state = %{
       id: state.id,
+      save_scheduled: save_scheduled,
       version: state.version + 1,
       contents: Delta.compose(state.contents, change),
       inverted_changes: [inverted | state.inverted_changes]
     }
 
-    PoexWeb.Endpoint.broadcast("pad:#{state.id}", "update", %{
+    PoexWeb.Endpoint.broadcast("pad:#{new_state.id}", "update", %{
       change: change,
       client_id: client_id
     })
 
-    {:reply, state.contents, state}
+    {:reply, new_state.contents, new_state}
   end
 
   # Fetch the current contents of the document
@@ -100,6 +113,7 @@ defmodule Poex.Pads.DocumentServer do
 
     state = %{
       id: state.id,
+      save_scheduled: state.save_scheduled,
       version: state.version - 1,
       contents: Delta.compose(state.contents, last_change),
       inverted_changes: changes
@@ -108,5 +122,13 @@ defmodule Poex.Pads.DocumentServer do
     {:reply, state.contents, state}
   end
 
+  @impl true
+  def handle_info(:save, state) do
+    state = Map.put(state, :save_scheduled, false)
+    Pads.update_pad_document(state.id, %{contents: state.contents})
+    PoexWeb.Endpoint.broadcast("pad:#{state.id}", "saved", %{})
+    {:noreply, state}
+  end
+
   defp via_tuple(id), do: {:via, Registry, {Poex.Pads.DocumentRegistry, id}}
 end