document_channel.ex

defmodule Docs.DocumentChannel do
  use Docs.Web, :channel
  alias Docs.Document
  import SweetXml

  def join("documents:" <> doc_id, params, socket) do
    send(self, {:after_join, params})
    {:ok, assign(socket, :doc_id, doc_id)}
  end

  def handle_info({:after_join, params}, socket) do
    doc = Repo.get(Document, socket.assigns.doc_id)
    messages = Repo.all(
      from m in assoc(doc, :messages),
        order_by: [desc: m.inserted_at],
        select: %{id: m.id, body: m.body},
        where: m.id > ^params["last_message_id"],
        limit: 100
    )
    push socket, "messages", %{messages: messages}
    {:noreply, socket}
  end

  def handle_in("text_change", %{"ops" => ops}, socket) do
    broadcast_from! socket, "text_change", %{
      ops: ops
    }
    {:reply, :ok, socket}
  end

  def handle_in("save", params, socket) do
    Document
    |> Repo.get(socket.assigns.doc_id)
    |> Document.changeset(params)
    |> Repo.update()
    |> case do
      {:ok, _document} ->
        {:reply, :ok, socket}
      {:error, changeset} ->
        {:reply, {:error, %{reasons: changeset}}, socket}
    end
  end

  def handle_in("new_message", params, socket) do
    changeset =
      Document
      |> Repo.get(socket.assigns.doc_id)
      |> Ecto.Model.build(:messages)
      |> Message.changeset(params)

    case Repo.insert(changeset) do
      {:ok, msg} ->
        broadcast! socket, "new_message", %{body: msg.body}
        {:reply, :ok, socket}

      {:error, changeset} ->
        {:reply, {:error, %{reasons: changeset}}, socket}
    end
  end


  def handle_in("compute_img", params, socket) do
    img_url =
      case Docs.InfoSys.compute_img(params["expr"]) do
        [%{img_url: img_url} | _] -> img_url
        _ -> ""
      end

    broadcast! socket, "insert_img", %{
      start: params["start"],
      end: params["end"],
      url: img_url
    }
    {:reply, :ok, socket}
  end

  def handle_in("selection_change", params, socket) do
    broadcast_from! socket, "selection_change", %{
      user_id: params["user_id"],
      username: params["username"],
      color: params["color"],
      end: params["end"]
    }
    {:reply, :ok, socket}
  end
end