Implement client joined rooms endpoint

Track which rooms a local account has joined
Add some documentation to modules

lib/matrix_server/schema/account.ex

@@ -3,7 +3,7 @@ defmodule MatrixServer.Account do
 
   import Ecto.{Changeset, Query}
 
-  alias MatrixServer.{Repo, Account, Device}
+  alias MatrixServer.{Repo, Account, Device, Room, JoinedRoom}
   alias MatrixServerWeb.Client.Request.{Register, Login}
   alias Ecto.Multi
 
@@ -17,6 +17,11 @@ defmodule MatrixServer.Account do
   schema "accounts" do
     field :password_hash, :string, redact: true
     has_many :devices, Device, foreign_key: :localpart
+
+    many_to_many :joined_rooms, Room,
+      join_through: JoinedRoom,
+      join_keys: [localpart: :localpart, room_id: :id]
+
     timestamps(updated_at: false)
   end
 

lib/matrix_server/schema/joined_room.ex

@@ -0,0 +1,16 @@
+defmodule MatrixServer.JoinedRoom do
+  use Ecto.Schema
+
+  alias MatrixServer.{Account, Room}
+
+  @primary_key false
+  schema "joined_rooms" do
+    belongs_to :account, Account,
+      foreign_key: :localpart,
+      references: :localpart,
+      type: :string,
+      primary_key: true
+
+    belongs_to :room, Room, primary_key: true, type: :string
+  end
+end