Create AnonymousUser model.

We want to start recording anonymous users so we can store
relevant data such as a fake name, fake avatar, and when
their chatroom was last viewed by an admin.

We generate the relevant migrations and add the fields we
need for an `anonymous_user`. Since the frontend generates
a UUID for every anonymous user, the UUID would be perfect as
`id` for our AnonymousUser records. We use the `uuid` type
for the `id` column of our AnonymousUser and set it to
not autogenerate an id. That way, we use the UUID passed to
us from the frontend as `id` every time we create a new
AnonymousUser record.

Now that we have an AnonymousUser, we can associate it with
Message so we can easily get all the messages sent by a user.
Note that there are a few extra steps for this because we
are using a `:uuid` type as `id` instead of the default
`:integer`.

mix.exs

@@ -21,6 +21,7 @@ defmodule PhoenixChat.Mixfile do
       applications: [
         :comeonin,
         :cowboy,
+        :faker,
         :gettext,
         :logger,
         :phoenix,
@@ -45,6 +46,7 @@ defmodule PhoenixChat.Mixfile do
       {:comeonin, "~> 2.3"},
       {:corsica, "~> 0.4"},
       {:cowboy, "~> 1.0"},
+      {:faker, "~> 0.7"},
       {:gettext, "~> 0.11"},
       {:guardian, "~> 0.10"},
       {:phoenix, "~> 1.2.0"},

mix.lock

@@ -7,6 +7,7 @@
   "db_connection": {:hex, :db_connection, "1.0.0-rc.5", "1d9ab6e01387bdf2de7a16c56866971f7c2f75aea7c69cae2a0346e4b537ae0d", [:mix], [{:connection, "~> 1.0.2", [hex: :connection, optional: false]}, {:poolboy, "~> 1.5", [hex: :poolboy, optional: true]}, {:sbroker, "~> 1.0.0-beta.3", [hex: :sbroker, optional: true]}]},
   "decimal": {:hex, :decimal, "1.1.2", "79a769d4657b2d537b51ef3c02d29ab7141d2b486b516c109642d453ee08e00c", [:mix], []},
   "ecto": {:hex, :ecto, "2.0.5", "7f4c79ac41ffba1a4c032b69d7045489f0069c256de606523c65d9f8188e502d", [:mix], [{:db_connection, "~> 1.0-rc.4", [hex: :db_connection, optional: true]}, {:decimal, "~> 1.1.2 or ~> 1.2", [hex: :decimal, optional: false]}, {:mariaex, "~> 0.7.7", [hex: :mariaex, optional: true]}, {:poison, "~> 1.5 or ~> 2.0", [hex: :poison, optional: true]}, {:poolboy, "~> 1.5", [hex: :poolboy, optional: false]}, {:postgrex, "~> 0.12.0", [hex: :postgrex, optional: true]}, {:sbroker, "~> 1.0-beta", [hex: :sbroker, optional: true]}]},
+  "faker": {:hex, :faker, "0.7.0", "2c42deeac7be717173c78c77fb3edc749fb5d5e460e33d01fe592ae99acc2f0d", [:mix], []},
   "fs": {:hex, :fs, "0.9.2", "ed17036c26c3f70ac49781ed9220a50c36775c6ca2cf8182d123b6566e49ec59", [:rebar], []},
   "gettext": {:hex, :gettext, "0.11.0", "80c1dd42d270482418fa158ec5ba073d2980e3718bacad86f3d4ad71d5667679", [:mix], []},
   "guardian": {:hex, :guardian, "0.12.0", "ab1f0a1ab0cd8f4f9c8cca6e28d61136ca682684cf0f82e55a50e8061be7575a", [:mix], [{:jose, "~> 1.6", [hex: :jose, optional: false]}, {:plug, "~> 1.0", [hex: :plug, optional: false]}, {:poison, ">= 1.3.0", [hex: :poison, optional: false]}, {:uuid, ">=1.1.1", [hex: :uuid, optional: false]}]},

priv/repo/migrations/20160915111446_create_anonymous_users.exs

@@ -0,0 +1,18 @@
+defmodule PhoenixChat.Repo.Migrations.CreateAnonymousUsers do
+  use Ecto.Migration
+
+  def change do
+    # We want to use a `uuid` as primary key so we need to set `primary_key: false`.
+    create table(:anonymous_users, primary_key: false) do
+      # We add the `:id` column manually with a type of `uuid` and set
+      # it as `primary_key`.
+      add :id, :uuid, primary_key: true
+      add :name, :string
+      add :avatar, :string
+      add :public_key, :string
+      add :last_viewed_by_admin_at, :datetime
+
+      timestamps
+    end
+  end
+end

priv/repo/migrations/20160915111609_message_belongs_to_anonymous_user.exs

@@ -0,0 +1,18 @@
+defmodule PhoenixChat.Repo.Migrations.MessageBelongsToAnonymousUser do
+  use Ecto.Migration
+
+  def up do
+    alter table(:messages) do
+      # We need to set `type` as `uuid` so it does not default to `integer`.
+      add :anonymous_user_id, references(:anonymous_users, on_delete: :nilify_all, type: :uuid)
+      remove :from
+    end
+  end
+
+  def down do
+    alter table(:messages) do
+      remove :anonymous_user_id
+      add :from, :string
+    end
+  end
+end

web/models/anonymous_user.ex

@@ -0,0 +1,65 @@
+defmodule PhoenixChat.AnonymousUser do
+  use PhoenixChat.Web, :model
+
+  alias PhoenixChat.Message
+
+  # Since we provide the `id` for our AnonymousUser record, we will need to set
+  # the primary key to not autogenerate it.
+  @primary_key {:id, :binary_id, autogenerate: false}
+  # We need to set `@foreign_key_type` below since it defaults to `:integer`.
+  # We are using a UUID as `id` so we need to set type as `:binary_id`.
+  @foreign_key_type :binary_id
+
+  schema "anonymous_users" do
+    field :name
+    field :avatar
+    field :public_key
+    field :last_viewed_by_admin_at, PhoenixChat.DateTime
+    has_many :messages, Message
+
+    timestamps
+  end
+
+  def changeset(model, params \\ :empty) do
+    model
+    |> cast(params, ~w(public_key id), ~w())
+    |> put_avatar
+    |> put_name
+  end
+
+  def last_viewed_changeset(model) do
+    params = %{last_viewed_by_admin_at: System.system_time(:milliseconds)}
+    model
+    |> cast(params, ~w(last_viewed_by_admin_at), [])
+  end
+
+  @doc """
+  This query returns all users and the respective last messages they
+  have sent.
+
+  Once the query is run, the return value is a tuple of two elements:
+  `{user, message}`
+  """
+  def by_public_key(public_key, limit \\ 20) do
+    from u in __MODULE__,
+      join: m in Message, on: m.anonymous_user_id == u.id,
+      where: u.public_key == ^public_key,
+      limit: ^limit,
+      distinct: u.id,
+      order_by: [desc: m.inserted_at],
+      select: {u, m}
+  end
+
+  # Set a fake name for our anonymous user every time we create one
+  defp put_name(changeset) do
+    name = (Faker.Color.fancy_name <> " " <> Faker.Company.buzzword()) |> String.downcase
+    changeset
+    |> put_change(:name, name)
+  end
+
+  # Set a fake avatar for our anonymous user every time we create one
+  defp put_avatar(changeset) do
+    changeset
+    |> put_change(:avatar, Faker.Avatar.image_url(25, 25))
+  end
+end

web/models/message.ex

@@ -1,18 +1,23 @@
 defmodule PhoenixChat.Message do
   use PhoenixChat.Web, :model
 
+  alias PhoenixChat.{DateTime, User, AnonymousUser}
+
   schema "messages" do
     field :body, :string
-    field :timestamp, PhoenixChat.DateTime
+    field :timestamp, DateTime
     field :room, :string
-    field :from, :string
-    belongs_to :user, PhoenixChat.User
+
+    belongs_to :user, User
+    # Note that we set `:type` below. This is so Ecto is aware the type of the
+    # foreign_key is not an `:integer` but a `:binary_id`.
+    belongs_to :user, AnonymousUser, type: :binary_id
 
     timestamps
   end
 
   @required_fields ~w(body timestamp room)
-  @optional_fields ~w(user_id from)
+  @optional_fields ~w(anonymous_user_id user_id)
 
   @doc """
   Creates a changeset based on the `model` and `params`.