Add endpoint for room creation

lib/matrix_server/room.ex

@@ -0,0 +1,29 @@
+defmodule MatrixServer.Room do
+  use Ecto.Schema
+
+  import Ecto.Changeset
+
+  alias __MODULE__
+  alias MatrixServerWeb.API.CreateRoom
+  alias Ecto.Multi
+
+  @primary_key {:id, :string, []}
+  schema "rooms" do
+    field :visibility, Ecto.Enum, values: [:public, :private]
+  end
+
+  def create(%CreateRoom{} = api) do
+    Multi.new()
+    |> Multi.insert(:room, Room.create_changeset(api))
+  end
+
+  def changeset(room, params \\ %{}) do
+    room
+    |> cast(params, [:visibility])
+  end
+
+  def create_changeset(%CreateRoom{} = api) do
+    %Room{visibility: api.visibility, id: MatrixServer.random_string(18)}
+    |> changeset()
+  end
+end