Chats: Basic implementation.

lib/pleroma/chat.ex

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+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Chat do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  alias Pleroma.User
+  alias Pleroma.Repo
+
+  @moduledoc """
+  Chat keeps a reference to DirectMessage conversations between a user and an recipient. The recipient can be a user (for now) or a group (not implemented yet).
+
+  It is a helper only, to make it easy to display a list of chats with other people, ordered by last bump. The actual messages are retrieved by querying the recipients of the ChatMessages.
+  """
+
+  schema "chats" do
+    belongs_to(:user, User, type: FlakeId.Ecto.CompatType)
+    field(:recipient, :string)
+    field(:unread, :integer, default: 0)
+
+    timestamps()
+  end
+
+  def creation_cng(struct, params) do
+    struct
+    |> cast(params, [:user_id, :recipient])
+    |> validate_required([:user_id, :recipient])
+    |> unique_constraint(:user_id, name: :chats_user_id_recipient_index)
+  end
+
+  def get_or_create(user_id, recipient) do
+    %__MODULE__{}
+    |> creation_cng(%{user_id: user_id, recipient: recipient})
+    |> Repo.insert(
+      on_conflict: [set: [updated_at: NaiveDateTime.utc_now()]],
+      conflict_target: [:user_id, :recipient]
+    )
+  end
+end

priv/repo/migrations/20200309123730_create_chats.exs

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+defmodule Pleroma.Repo.Migrations.CreateChats do
+  use Ecto.Migration
+
+  def change do
+    create table(:chats) do
+      add(:user_id, references(:users, type: :uuid))
+      # Recipient is an ActivityPub id, to future-proof for group support.
+      add(:recipient, :string)
+      add(:unread, :integer, default: 0)
+      timestamps()
+    end
+
+    # There's only one chat between a user and a recipient.
+    create(index(:chats, [:user_id, :recipient], unique: true))
+  end
+end

test/chat_test.exs

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+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.ChatTest do
+  use Pleroma.DataCase, async: true
+
+  alias Pleroma.Chat
+
+  import Pleroma.Factory
+
+  describe "creation and getting" do
+    test "it creates a chat for a user and recipient" do
+      user = insert(:user)
+      other_user = insert(:user)
+
+      {:ok, chat} = Chat.get_or_create(user.id, other_user.ap_id)
+
+      assert chat.id
+    end
+
+    test "it returns a chat for a user and recipient if it already exists" do
+      user = insert(:user)
+      other_user = insert(:user)
+
+      {:ok, chat} = Chat.get_or_create(user.id, other_user.ap_id)
+      {:ok, chat_two} = Chat.get_or_create(user.id, other_user.ap_id)
+
+      assert chat.id == chat_two.id
+    end
+
+    test "a returning chat will have an updated `update_at` field" do
+      user = insert(:user)
+      other_user = insert(:user)
+
+      {:ok, chat} = Chat.get_or_create(user.id, other_user.ap_id)
+      :timer.sleep(1500)
+      {:ok, chat_two} = Chat.get_or_create(user.id, other_user.ap_id)
+
+      assert chat.id == chat_two.id
+      assert chat.updated_at != chat_two.updated_at
+    end
+  end
+end