Merge pull request 'Add grouped notifications API' (#7910) from issue-7905-grouped-notifications into develop

Reviewed-on: https://git.pleroma.social/pleroma/pleroma/pulls/7910
Reviewed-by: Phantasm <phnt@noreply.git.pleroma.social>

changelog.d/grouped-notifications-api.add

@@ -0,0 +1 @@
+Add Mastodon-compatible grouped notifications API endpoints under `/api/v2/notifications` for newly-created notifications

lib/pleroma/notification.ex

@@ -35,6 +35,7 @@ defmodule Pleroma.Notification do
     # remember to add a migration to add it to the `notifications_type` enum
     # as well.
     field(:type, :string)
+    field(:group_key, :string)
     belongs_to(:user, User, type: FlakeId.Ecto.CompatType)
     belongs_to(:activity, Activity, type: FlakeId.Ecto.CompatType)
 
@@ -49,7 +50,7 @@ defmodule Pleroma.Notification do
         |> type_from_activity()
 
       notification
-      |> changeset(%{type: type})
+      |> changeset(%{type: type, group_key: grouped_notification_key(type, activity)})
       |> Repo.update()
     end
   end
@@ -62,6 +63,99 @@ defmodule Pleroma.Notification do
     |> Repo.aggregate(:count, :id)
   end
 
+  @groupable_notification_types ~w{favourite follow reblog}
+  @group_bucket_seconds 12 * 60 * 60
+
+  def groupable_notification_types, do: @groupable_notification_types
+
+  def group_notifications(notifications, grouped_types \\ nil) do
+    grouped_types = normalize_grouped_types(grouped_types)
+
+    {group_keys, grouped_notifications} =
+      Enum.reduce(notifications, {[], %{}}, fn notification,
+                                               {group_keys, grouped_notifications} ->
+        group_key = group_key(notification, grouped_types)
+
+        if Map.has_key?(grouped_notifications, group_key) do
+          {group_keys, Map.update!(grouped_notifications, group_key, &[notification | &1])}
+        else
+          {[group_key | group_keys], Map.put(grouped_notifications, group_key, [notification])}
+        end
+      end)
+
+    group_keys
+    |> Enum.reverse()
+    |> Enum.map(fn group_key ->
+      grouped_notifications
+      |> Map.fetch!(group_key)
+      |> Enum.reverse()
+    end)
+  end
+
+  def group_key(notification, grouped_types \\ nil)
+
+  def group_key(%Notification{} = notification, nil) do
+    group_key(notification, @groupable_notification_types)
+  end
+
+  def group_key(%Notification{type: type, group_key: group_key} = notification, grouped_types) do
+    grouped_types = normalize_grouped_types(grouped_types)
+
+    if type in @groupable_notification_types and type in grouped_types and is_binary(group_key) do
+      group_key
+    else
+      ungrouped_group_key(notification)
+    end
+  end
+
+  def normalize_grouped_types(nil), do: @groupable_notification_types
+  def normalize_grouped_types(types) when is_list(types), do: types
+  def normalize_grouped_types(type), do: [type]
+
+  defp ungrouped_group_key(%Notification{id: id}), do: "ungrouped-#{id}"
+
+  defp grouped_notification_key(type, activity) when type in @groupable_notification_types do
+    with target_id when is_binary(target_id) <- group_target_id(type, activity) do
+      # Mastodon uses Redis to reuse a recent bucket for rolling 12h windows. Pleroma keeps keys
+      # deterministic and self-contained; clients must treat group_key as opaque either way.
+      "#{type}-#{target_id}-#{group_time_bucket(activity)}"
+    end
+  end
+
+  defp grouped_notification_key(_type, _activity), do: nil
+
+  defp group_time_bucket(%Activity{inserted_at: inserted_at}) when not is_nil(inserted_at) do
+    inserted_at
+    |> NaiveDateTime.to_erl()
+    |> :calendar.datetime_to_gregorian_seconds()
+    |> div(@group_bucket_seconds)
+  end
+
+  defp group_time_bucket(_),
+    do: group_time_bucket(%Activity{inserted_at: NaiveDateTime.utc_now()})
+
+  defp group_target_id(type, activity) when type in ["favourite", "reblog"] do
+    with object_id when is_binary(object_id) <- object_id_for(activity),
+         %Activity{id: id} <- Activity.get_create_by_object_ap_id(object_id) do
+      to_string(id)
+    else
+      _ -> nil
+    end
+  end
+
+  defp group_target_id("follow", %{data: %{"object" => ap_id}}) do
+    case User.get_cached_by_ap_id(ap_id) do
+      %User{id: id} -> to_string(id)
+      _ -> nil
+    end
+  end
+
+  defp group_target_id(_, _), do: nil
+
+  defp object_id_for(%{data: %{"object" => %{"id" => id}}}) when is_binary(id), do: id
+  defp object_id_for(%{data: %{"object" => id}}) when is_binary(id), do: id
+  defp object_id_for(_), do: nil
+
   @notification_types ~w{
     favourite
     follow
@@ -79,7 +173,7 @@ defmodule Pleroma.Notification do
 
   def changeset(%Notification{} = notification, attrs) do
     notification
-    |> cast(attrs, [:seen, :type])
+    |> cast(attrs, [:seen, :type, :group_key])
     |> validate_inclusion(:type, @notification_types)
   end
 
@@ -458,7 +552,8 @@ defmodule Pleroma.Notification do
           user_id: user.id,
           activity: activity,
           seen: mark_as_read?(activity, user),
-          type: type
+          type: type,
+          group_key: grouped_notification_key(type, activity)
         })
         |> Marker.multi_set_last_read_id(user, "notifications")
         |> Repo.transaction()

lib/pleroma/web/api_spec/operations/notification_operation.ex

@@ -3,7 +3,6 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.Web.ApiSpec.NotificationOperation do
-  alias OpenApiSpex.Operation
   alias OpenApiSpex.Operation
   alias OpenApiSpex.Schema
   alias Pleroma.Web.ApiSpec.Schemas.Account
@@ -91,6 +90,79 @@ defmodule Pleroma.Web.ApiSpec.NotificationOperation do
     }
   end
 
+  def grouped_index_operation do
+    %Operation{
+      tags: ["Notifications"],
+      summary: "Retrieve grouped notifications",
+      description: "Notifications concerning the user, grouped by supported notification types.",
+      operationId: "NotificationController.grouped_index",
+      security: [%{"oAuth" => ["read:notifications"]}],
+      parameters: grouped_notification_params() ++ pagination_params(),
+      responses: %{
+        200 => Operation.response("Grouped notifications", "application/json", grouped_result()),
+        404 => Operation.response("Error", "application/json", ApiError)
+      }
+    }
+  end
+
+  def show_group_operation do
+    %Operation{
+      tags: ["Notifications"],
+      summary: "Retrieve a notification group",
+      operationId: "NotificationController.show_group",
+      security: [%{"oAuth" => ["read:notifications"]}],
+      parameters: [group_key_param()],
+      responses: %{
+        200 => Operation.response("Grouped notifications", "application/json", grouped_result()),
+        404 => Operation.response("Error", "application/json", ApiError)
+      }
+    }
+  end
+
+  def group_accounts_operation do
+    %Operation{
+      tags: ["Notifications"],
+      summary: "Retrieve notification group accounts",
+      operationId: "NotificationController.group_accounts",
+      security: [%{"oAuth" => ["read:notifications"]}],
+      parameters: [group_key_param()],
+      responses: %{
+        200 =>
+          Operation.response("Accounts", "application/json", %Schema{
+            type: :array,
+            items: Account
+          })
+      }
+    }
+  end
+
+  def unread_count_operation do
+    %Operation{
+      tags: ["Notifications"],
+      summary: "Retrieve unread grouped notification count",
+      operationId: "NotificationController.unread_count",
+      security: [%{"oAuth" => ["read:notifications"]}],
+      parameters:
+        grouped_notification_params() ++
+          [
+            Operation.parameter(
+              :limit,
+              :query,
+              %Schema{type: :integer},
+              "Maximum number of notifications to count"
+            )
+          ],
+      responses: %{
+        200 =>
+          Operation.response("Unread notification group count", "application/json", %Schema{
+            type: :object,
+            properties: %{count: %Schema{type: :integer}}
+          }),
+        404 => Operation.response("Error", "application/json", ApiError)
+      }
+    }
+  end
+
   def clear_operation do
     %Operation{
       tags: ["Notifications"],
@@ -114,6 +186,18 @@ defmodule Pleroma.Web.ApiSpec.NotificationOperation do
     }
   end
 
+  def dismiss_group_operation do
+    %Operation{
+      tags: ["Notifications"],
+      summary: "Dismiss a notification group",
+      description: "Clear all notifications in a notification group from the server.",
+      operationId: "NotificationController.dismiss_group",
+      parameters: [group_key_param()],
+      security: [%{"oAuth" => ["write:notifications"]}],
+      responses: %{200 => empty_object_response()}
+    }
+  end
+
   def dismiss_via_body_operation do
     %Operation{
       tags: ["Notifications"],
@@ -184,7 +268,7 @@ defmodule Pleroma.Web.ApiSpec.NotificationOperation do
       },
       example: %{
         "id" => "34975861",
-        "group-key" => "ungrouped-34975861",
+        "group_key" => "ungrouped-34975861",
         "type" => "mention",
         "created_at" => "2019-11-23T07:49:02.064Z",
         "account" => Account.schema().example,
@@ -194,6 +278,73 @@ defmodule Pleroma.Web.ApiSpec.NotificationOperation do
     }
   end
 
+  defp grouped_result do
+    %Schema{
+      title: "GroupedNotificationsResults",
+      type: :object,
+      properties: %{
+        accounts: %Schema{type: :array, items: Account},
+        statuses: %Schema{type: :array, items: Status},
+        notification_groups: %Schema{type: :array, items: notification_group()}
+      },
+      required: [:accounts, :statuses, :notification_groups]
+    }
+  end
+
+  defp notification_group do
+    %Schema{
+      title: "NotificationGroup",
+      type: :object,
+      properties: %{
+        group_key: %Schema{type: :string},
+        notifications_count: %Schema{type: :integer},
+        type: notification_type(),
+        most_recent_notification_id: %Schema{type: :string},
+        page_min_id: %Schema{type: :string, nullable: true},
+        page_max_id: %Schema{type: :string, nullable: true},
+        latest_page_notification_at: %Schema{type: :string, format: :"date-time", nullable: true},
+        sample_account_ids: %Schema{type: :array, items: %Schema{type: :string}},
+        status_id: %Schema{type: :string, nullable: true}
+      },
+      required: [
+        :group_key,
+        :notifications_count,
+        :type,
+        :most_recent_notification_id,
+        :sample_account_ids
+      ]
+    }
+  end
+
+  defp grouped_notification_params do
+    [
+      Operation.parameter(
+        :exclude_types,
+        :query,
+        %Schema{type: :array, items: notification_type()},
+        "Array of types to exclude"
+      ),
+      Operation.parameter(
+        :account_id,
+        :query,
+        %Schema{type: :string},
+        "Return only notifications received from this account"
+      ),
+      Operation.parameter(
+        :types,
+        :query,
+        %Schema{type: :array, items: notification_type()},
+        "Include the notifications for activities with the given types"
+      ),
+      Operation.parameter(
+        :grouped_types,
+        :query,
+        %Schema{type: :array, items: notification_type()},
+        "Notification types that may be grouped"
+      )
+    ]
+  end
+
   defp notification_type do
     %Schema{
       type: :string,
@@ -239,4 +390,11 @@ defmodule Pleroma.Web.ApiSpec.NotificationOperation do
       required: true
     )
   end
+
+  defp group_key_param do
+    Operation.parameter(:group_key, :path, :string, "Notification group key",
+      example: "favourite-123",
+      required: true
+    )
+  end
 end

lib/pleroma/web/controller_helper.ex

@@ -55,16 +55,28 @@ defmodule Pleroma.Web.ControllerHelper do
 
   # TODO: Only fetch the params from open_api_spex when everything is converted
   @id_keys Pagination.page_keys() -- ["limit", "order"]
+  @id_key_atoms Enum.map(@id_keys, &String.to_atom/1)
+  @drop_id_params_key :drop_id_params
   defp build_pagination_fields(conn, min_id, max_id, extra_params, order) do
+    drop_id_params? = Map.get(extra_params, @drop_id_params_key, false)
+    extra_params = Map.delete(extra_params, @drop_id_params_key)
+
+    path_param_keys =
+      conn.path_params
+      |> Map.keys()
+      |> Enum.flat_map(&[&1, String.to_existing_atom(&1)])
+
     params =
       if Map.has_key?(conn.private, :open_api_spex) do
         get_in(conn, [Access.key(:private), Access.key(:open_api_spex), Access.key(:params)])
       else
         conn.params
       end
-      |> Map.drop(Map.keys(conn.path_params) |> Enum.map(&String.to_existing_atom/1))
+      |> Map.drop(path_param_keys)
       |> Map.merge(extra_params)
-      |> Map.drop(@id_keys)
+      # Some OpenApiSpex routes cast cursor params to atoms. Keep the historical default for
+      # existing endpoints, but allow grouped notifications to opt out of stale request cursors.
+      |> Map.drop(@id_keys ++ if(drop_id_params?, do: @id_key_atoms, else: []))
 
     {{next_id, nid}, {prev_id, pid}} =
       if order == :desc,

lib/pleroma/web/mastodon_api/controllers/notification_controller.ex

@@ -5,13 +5,17 @@
 defmodule Pleroma.Web.MastodonAPI.NotificationController do
   use Pleroma.Web, :controller
 
-  import Pleroma.Web.ControllerHelper, only: [add_link_headers: 2]
+  import Pleroma.Web.ControllerHelper, only: [add_link_headers: 2, add_link_headers: 3]
 
   alias Pleroma.Notification
+  alias Pleroma.User
+  alias Pleroma.Web.MastodonAPI.AccountView
   alias Pleroma.Web.MastodonAPI.MastodonAPI
   alias Pleroma.Web.Plugs.OAuthScopesPlug
 
-  @oauth_read_actions [:show, :index]
+  # Mastodon's docs currently list write:notifications for group accounts, but the endpoint is
+  # read-only and Mastodon's implementation accepts read:notifications. Prefer least privilege.
+  @oauth_read_actions [:show, :index, :grouped_index, :show_group, :group_accounts, :unread_count]
 
   plug(Pleroma.Web.ApiSpec.CastAndValidate, replace_params: false)
 
@@ -39,7 +43,7 @@ defmodule Pleroma.Web.MastodonAPI.NotificationController do
 
   # GET /api/v1/notifications
   def index(%{private: %{open_api_spex: %{params: %{account_id: account_id} = params}}} = conn, _) do
-    case Pleroma.User.get_cached_by_id(account_id) do
+    case User.get_cached_by_id(account_id) do
       %{ap_id: account_ap_id} ->
         params =
           params
@@ -59,10 +63,108 @@ defmodule Pleroma.Web.MastodonAPI.NotificationController do
     do_get_notifications(conn, params)
   end
 
+  # GET /api/v2/notifications
+  def grouped_index(
+        %{private: %{open_api_spex: %{params: %{account_id: account_id} = params}}} = conn,
+        _
+      ) do
+    case User.get_cached_by_id(account_id) do
+      %{ap_id: account_ap_id} ->
+        params =
+          params
+          |> Map.delete(:account_id)
+          |> Map.put(:account_ap_id, account_ap_id)
+
+        do_get_grouped_notifications(conn, params)
+
+      _ ->
+        conn
+        |> put_status(:not_found)
+        |> json(%{"error" => "Account is not found"})
+    end
+  end
+
+  def grouped_index(%{private: %{open_api_spex: %{params: params}}} = conn, _) do
+    do_get_grouped_notifications(conn, params)
+  end
+
+  # GET /api/v2/notifications/:group_key
+  def show_group(
+        %{assigns: %{user: user}, private: %{open_api_spex: %{params: %{group_key: group_key}}}} =
+          conn,
+        _
+      ) do
+    {notifications, notification_group_counts, notification_group_bounds} =
+      MastodonAPI.get_notification_group_result(user, group_key, %{})
+
+    if Enum.empty?(notifications) do
+      conn
+      |> put_status(:not_found)
+      |> json(%{"error" => "Notification group is not found"})
+    else
+      grouped_types = if String.starts_with?(group_key, "ungrouped-"), do: [], else: nil
+
+      render(conn, "grouped_index.json",
+        notification_groups: [notifications],
+        notification_group_counts: notification_group_counts,
+        notification_group_bounds: notification_group_bounds,
+        for: user,
+        grouped_types: grouped_types,
+        include_page_metadata: false
+      )
+    end
+  end
+
+  # GET /api/v2/notifications/:group_key/accounts
+  def group_accounts(
+        %{assigns: %{user: user}, private: %{open_api_spex: %{params: %{group_key: group_key}}}} =
+          conn,
+        _
+      ) do
+    # Mastodon paginates this endpoint in code, but the public docs say it returns accounts of all
+    # notifications in the group and do not document cursor params here. Follow the documented API.
+    users = MastodonAPI.get_notification_group_accounts(user, group_key)
+
+    json(conn, AccountView.render("index.json", %{users: users, for: user}))
+  end
+
+  # GET /api/v2/notifications/unread_count
+  def unread_count(
+        %{private: %{open_api_spex: %{params: %{account_id: account_id} = params}}} = conn,
+        _
+      ) do
+    case User.get_cached_by_id(account_id) do
+      %{ap_id: account_ap_id} ->
+        params =
+          params
+          |> Map.delete(:account_id)
+          |> Map.put(:account_ap_id, account_ap_id)
+
+        do_get_unread_group_count(conn, params)
+
+      _ ->
+        conn
+        |> put_status(:not_found)
+        |> json(%{"error" => "Account is not found"})
+    end
+  end
+
+  def unread_count(%{private: %{open_api_spex: %{params: params}}} = conn, _) do
+    do_get_unread_group_count(conn, params)
+  end
+
+  # POST /api/v2/notifications/:group_key/dismiss
+  def dismiss_group(
+        %{assigns: %{user: user}, private: %{open_api_spex: %{params: %{group_key: group_key}}}} =
+          conn,
+        _
+      ) do
+    MastodonAPI.dismiss_notification_group(user, group_key)
+    json(conn, %{})
+  end
+
   defp do_get_notifications(%{assigns: %{user: user}} = conn, params) do
-    params =
+    params = normalize_notification_params(params)
-      Map.new(params, fn {k, v} -> {to_string(k), v} end)
-      |> Map.put_new("types", Map.get(params, :include_types, @default_notification_types))
 
     notifications = MastodonAPI.get_notifications(user, params)
 
@@ -74,6 +176,35 @@ defmodule Pleroma.Web.MastodonAPI.NotificationController do
     )
   end
 
+  defp do_get_grouped_notifications(%{assigns: %{user: user}} = conn, params) do
+    params = normalize_notification_params(params)
+
+    {notification_groups, page_notifications, notification_group_counts,
+     notification_group_bounds} =
+      MastodonAPI.get_grouped_notification_page(user, params)
+
+    conn
+    |> add_link_headers(page_notifications, %{drop_id_params: true})
+    |> render("grouped_index.json",
+      notification_groups: notification_groups,
+      notification_group_counts: notification_group_counts,
+      notification_group_bounds: notification_group_bounds,
+      for: user,
+      grouped_types: params["grouped_types"]
+    )
+  end
+
+  defp do_get_unread_group_count(%{assigns: %{user: user}} = conn, params) do
+    params = normalize_notification_params(params)
+    json(conn, %{count: MastodonAPI.unread_notification_group_count(user, params)})
+  end
+
+  defp normalize_notification_params(params) do
+    params
+    |> Map.new(fn {k, v} -> {to_string(k), v} end)
+    |> Map.put_new("types", Map.get(params, :include_types, @default_notification_types))
+  end
+
   # GET /api/v1/notifications/:id
   def show(%{assigns: %{user: user}, private: %{open_api_spex: %{params: %{id: id}}}} = conn, _) do
     with {:ok, notification} <- Notification.get(user, id) do

lib/pleroma/web/mastodon_api/mastodon_api.ex

@@ -6,12 +6,16 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPI do
   import Ecto.Query
   import Ecto.Changeset
 
+  alias Pleroma.Marker
   alias Pleroma.Notification
   alias Pleroma.Pagination
+  alias Pleroma.Repo
   alias Pleroma.ScheduledActivity
   alias Pleroma.User
   alias Pleroma.Web.CommonAPI
 
+  @notification_group_sample_limit 8
+
   @spec follow(User.t(), User.t(), map) :: {:ok, User.t()} | {:error, String.t()}
   def follow(follower, followed, params \\ %{}) do
     result =
@@ -61,29 +65,356 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPI do
   end
 
   def get_notifications(user, params \\ %{}) do
-    options =
+    user
-      cast_params(params) |> Map.update(:include_types, [], fn include_types -> include_types end)
+    |> notifications_query(params)
+    |> Pagination.fetch_paginated(params)
+  end
 
-    options =
+  def get_grouped_notification_page(user, params \\ %{}) do
-      if ("pleroma:report" not in options.include_types and
+    grouped_types =
-            User.privileged?(user, :reports_manage_reports)) or
+      params
-           User.privileged?(user, :reports_manage_reports) do
+      |> Map.get("grouped_types")
-        options
+      |> Notification.normalize_grouped_types()
-      else
+
-        options
+    query = notifications_query(user, params)
-        |> Map.update(:exclude_types, ["pleroma:report"], fn current_exclude_types ->
+    {order, cursor_filters} = group_pagination(params)
-          current_exclude_types ++ ["pleroma:report"]
+
-        end)
+    group_rows =
-      end
+      query
+      |> notification_group_rows(grouped_types, grouped_limit(params), order, cursor_filters)
+
+    group_rows = if order == :asc, do: Enum.reverse(group_rows), else: group_rows
+
+    page_notifications = representative_notifications(query, group_rows)
+
+    notification_groups =
+      Enum.map(group_rows, &notification_group_sample(user, params, &1.group_key))
+
+    {
+      notification_groups,
+      page_notifications,
+      notification_group_counts(group_rows),
+      notification_group_bounds(group_rows)
+    }
+  end
+
+  def get_notification_group_result(user, group_key, params \\ %{}) do
+    notifications = notification_group_sample(user, params, group_key)
+    metadata = notification_group_metadata(user, group_key, params)
+
+    if Enum.empty?(notifications) or is_nil(metadata) do
+      {[], %{}, %{}}
+    else
+      {
+        notifications,
+        %{group_key => metadata.notifications_count},
+        %{group_key => Map.drop(metadata, [:notifications_count])}
+      }
+    end
+  end
+
+  def get_notification_group(user, group_key, params \\ %{})
+
+  def get_notification_group(user, "ungrouped-" <> notification_id, _params) do
+    case Notification.get(user, notification_id) do
+      {:ok, notification} -> [notification]
+      _ -> []
+    end
+  end
+
+  def get_notification_group(user, group_key, params) do
+    notification_group_sample(user, params, group_key)
+  end
+
+  def get_notification_group_accounts(user, "ungrouped-" <> notification_id) do
+    with {:ok, notification} <- Notification.get(user, notification_id),
+         %User{} = actor <- User.get_cached_by_ap_id(notification.activity.data["actor"]) do
+      [actor]
+    else
+      _ -> []
+    end
+  end
+
+  def get_notification_group_accounts(user, group_key) do
+    user
+    |> notification_group_query(group_key, %{})
+    |> exclude(:preload)
+    |> distinct(true)
+    |> select([user_actor: user_actor], user_actor)
+    |> Repo.all()
+  end
+
+  def dismiss_notification_group(user, "ungrouped-" <> notification_id) do
+    Notification.destroy_multiple(user, [notification_id])
+  end
+
+  def dismiss_notification_group(%User{id: user_id}, group_key) do
+    Notification
+    |> where([n], n.user_id == ^user_id and n.group_key == ^group_key)
+    |> Repo.delete_all()
+  end
+
+  defp group_pagination(params) do
+    cond do
+      min_id = Map.get(params, "min_id") ->
+        cursor_filters = [{:gt, min_id}]
+
+        cursor_filters =
+          case Map.get(params, "max_id") do
+            nil -> cursor_filters
+            max_id -> [{:lt, max_id} | cursor_filters]
+          end
+
+        {:asc, cursor_filters}
+
+      since_id = Map.get(params, "since_id") ->
+        {:desc, [{:gt, since_id}]}
+
+      max_id = Map.get(params, "max_id") ->
+        {:desc, [{:lt, max_id}]}
+
+      true ->
+        {:desc, []}
+    end
+  end
+
+  defp grouped_limit(params) do
+    params
+    |> Map.get("limit", 40)
+    |> parse_limit(40)
+    |> min(80)
+  end
+
+  def unread_notification_group_count(user, params \\ %{}) do
+    grouped_types =
+      params
+      |> Map.get("grouped_types")
+      |> Notification.normalize_grouped_types()
+
+    limit = unread_count_limit(params)
+
+    user
+    |> notifications_query(params)
+    # The grouped API docs define unread by the notifications marker, not by Pleroma's per-row
+    # seen flag used by the v1 unread count. Keep this marker-based for Mastodon clients.
+    |> restrict_after_marker(notification_marker_last_read_id(user))
+    |> notification_group_rows(grouped_types, limit, :desc, [])
+    |> length()
+  end
+
+  defp notification_group_rows(query, grouped_types, group_limit, :desc, cursor_filters) do
+    query
+    |> notification_group_keyed_query(grouped_types)
+    |> group_by([n], n.group_key)
+    |> apply_group_cursor_filters(cursor_filters)
+    |> select([n], %{
+      group_key: n.group_key,
+      representative_id: max(n.id),
+      notifications_count: count(n.id),
+      page_min_id: min(n.id),
+      page_max_id: max(n.id),
+      latest_page_notification_at: max(n.inserted_at)
+    })
+    |> order_by([n], desc: max(n.id))
+    |> limit(^group_limit)
+    |> Repo.all()
+  end
+
+  defp notification_group_rows(query, grouped_types, group_limit, :asc, cursor_filters) do
+    query
+    |> notification_group_keyed_query(grouped_types)
+    |> group_by([n], n.group_key)
+    |> apply_group_cursor_filters(cursor_filters)
+    |> select([n], %{
+      group_key: n.group_key,
+      representative_id: max(n.id),
+      notifications_count: count(n.id),
+      page_min_id: min(n.id),
+      page_max_id: max(n.id),
+      latest_page_notification_at: max(n.inserted_at)
+    })
+    |> order_by([n], asc: max(n.id))
+    |> limit(^group_limit)
+    |> Repo.all()
+  end
+
+  defp apply_group_cursor_filters(query, []), do: query
+
+  defp apply_group_cursor_filters(query, [{:gt, id} | rest]) do
+    query
+    |> having([n], max(n.id) > ^id)
+    |> apply_group_cursor_filters(rest)
+  end
+
+  defp apply_group_cursor_filters(query, [{:lt, id} | rest]) do
+    query
+    |> having([n], max(n.id) < ^id)
+    |> apply_group_cursor_filters(rest)
+  end
+
+  defp notification_group_keyed_query(query, grouped_types) do
+    query
+    |> exclude(:preload)
+    |> select([n], %{
+      id: n.id,
+      inserted_at: n.inserted_at,
+      group_key:
+        fragment(
+          "CASE WHEN ? IS NOT NULL AND ?::text = ANY(?) THEN ? ELSE 'ungrouped-' || ?::text END",
+          n.group_key,
+          n.type,
+          type(^grouped_types, {:array, :string}),
+          n.group_key,
+          n.id
+        )
+    })
+    |> subquery()
+  end
+
+  defp representative_notifications(_query, []), do: []
+
+  defp representative_notifications(query, group_rows) do
+    representative_ids = Enum.map(group_rows, & &1.representative_id)
+
+    notifications_by_id =
+      query
+      |> where([n], n.id in ^representative_ids)
+      |> Repo.all()
+      |> Map.new(&{to_string(&1.id), &1})
+
+    group_rows
+    |> Enum.map(&Map.get(notifications_by_id, to_string(&1.representative_id)))
+    |> Enum.filter(& &1)
+  end
+
+  defp notification_group_counts(group_rows) do
+    Map.new(group_rows, &{&1.group_key, &1.notifications_count})
+  end
+
+  defp notification_group_bounds(group_rows) do
+    Map.new(group_rows, fn row ->
+      {row.group_key,
+       %{
+         page_min_id: row.page_min_id,
+         page_max_id: row.page_max_id,
+         latest_page_notification_at: row.latest_page_notification_at
+       }}
+    end)
+  end
+
+  defp notification_group_sample(user, _params, "ungrouped-" <> notification_id) do
+    case Notification.get(user, notification_id) do
+      {:ok, notification} -> [notification]
+      _ -> []
+    end
+  end
+
+  defp notification_group_sample(user, params, group_key) do
+    user
+    |> notification_group_query(group_key, params)
+    |> order_by([n], desc: n.id)
+    |> limit(^@notification_group_sample_limit)
+    |> Repo.all()
+  end
+
+  defp notification_group_metadata(user, "ungrouped-" <> notification_id, _params) do
+    case Notification.get(user, notification_id) do
+      {:ok, notification} ->
+        %{
+          notifications_count: 1,
+          page_min_id: notification.id,
+          page_max_id: notification.id,
+          latest_page_notification_at: notification.inserted_at
+        }
+
+      _ ->
+        nil
+    end
+  end
+
+  defp notification_group_metadata(user, group_key, params) do
+    user
+    |> notification_group_query(group_key, params)
+    |> exclude(:preload)
+    |> select([n], %{
+      notifications_count: count(n.id),
+      page_min_id: min(n.id),
+      page_max_id: max(n.id),
+      latest_page_notification_at: max(n.inserted_at)
+    })
+    |> Repo.one()
+    |> case do
+      %{notifications_count: 0} -> nil
+      metadata -> metadata
+    end
+  end
+
+  defp notification_group_query(user, group_key, params) do
+    user
+    |> notifications_query(params)
+    |> where([n], n.group_key == ^group_key)
+  end
+
+  defp notification_marker_last_read_id(user) do
+    Marker
+    |> where([m], m.user_id == ^user.id and m.timeline == "notifications")
+    |> select([m], m.last_read_id)
+    |> Repo.one()
+  end
+
+  defp restrict_after_marker(query, last_read_id)
+       when is_binary(last_read_id) and last_read_id != "" do
+    where(query, [n], n.id > ^last_read_id)
+  end
+
+  defp restrict_after_marker(query, _last_read_id), do: query
+
+  defp notifications_query(user, params) do
+    options = notification_options(user, params)
 
     user
     |> Notification.for_user_query(options)
     |> restrict(:types, options)
     |> restrict(:exclude_types, options)
     |> restrict(:account_ap_id, options)
-    |> Pagination.fetch_paginated(params)
   end
 
+  defp notification_options(user, params) do
+    options =
+      params
+      |> cast_params()
+      |> Map.update(:include_types, [], fn include_types -> include_types end)
+
+    if ("pleroma:report" not in options.include_types and
+          User.privileged?(user, :reports_manage_reports)) or
+         User.privileged?(user, :reports_manage_reports) do
+      options
+    else
+      options
+      |> Map.update(:exclude_types, ["pleroma:report"], fn current_exclude_types ->
+        current_exclude_types ++ ["pleroma:report"]
+      end)
+    end
+  end
+
+  defp unread_count_limit(params) do
+    params
+    |> Map.get("limit", 100)
+    |> parse_limit(100)
+    |> min(1000)
+  end
+
+  defp parse_limit(limit, _default) when is_integer(limit) and limit > 0, do: limit
+
+  defp parse_limit(limit, default) when is_binary(limit) do
+    case Integer.parse(limit) do
+      {limit, _} when limit > 0 -> limit
+      _ -> default
+    end
+  end
+
+  defp parse_limit(_, default), do: default
+
   def get_scheduled_activities(user, params \\ %{}) do
     user
     |> ScheduledActivity.for_user_query()
@@ -95,6 +426,8 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPI do
       exclude_types: {:array, :string},
       types: {:array, :string},
       exclude_visibilities: {:array, :string},
+      grouped_types: {:array, :string},
+      limit: :integer,
       reblogs: :boolean,
       with_muted: :boolean,
       account_ap_id: :string,

lib/pleroma/web/mastodon_api/views/notification_view.ex

@@ -72,6 +72,58 @@ defmodule Pleroma.Web.MastodonAPI.NotificationView do
     safe_render_many(notifications, NotificationView, "show.json", opts)
   end
 
+  def render("grouped_index.json", %{notifications: notifications} = opts) do
+    grouped_types = Notification.normalize_grouped_types(opts[:grouped_types])
+
+    opts
+    |> Map.delete(:notifications)
+    |> Map.put(
+      :notification_groups,
+      Notification.group_notifications(notifications, grouped_types)
+    )
+    |> then(&render("grouped_index.json", &1))
+  end
+
+  def render(
+        "grouped_index.json",
+        %{notification_groups: notification_groups, for: reading_user} = opts
+      ) do
+    grouped_types = Notification.normalize_grouped_types(opts[:grouped_types])
+    notification_group_counts = Map.get(opts, :notification_group_counts, %{})
+    notification_group_bounds = Map.get(opts, :notification_group_bounds, %{})
+    include_page_metadata = Map.get(opts, :include_page_metadata, true)
+
+    statuses =
+      notification_groups
+      |> Enum.map(&List.first/1)
+      |> Enum.map(&render("show.json", %{notification: &1, for: reading_user}))
+      |> Enum.map(& &1[:status])
+      |> Enum.filter(& &1)
+      |> Enum.uniq_by(& &1[:id])
+
+    actors =
+      notification_groups
+      |> List.flatten()
+      |> notification_actors()
+
+    %{
+      accounts: AccountView.render("index.json", %{users: actors, for: reading_user}),
+      statuses: statuses,
+      notification_groups:
+        Enum.map(
+          notification_groups,
+          &render_group(
+            &1,
+            reading_user,
+            grouped_types,
+            notification_group_counts,
+            notification_group_bounds,
+            include_page_metadata
+          )
+        )
+    }
+  end
+
   def render(
         "show.json",
         %{
@@ -95,7 +147,7 @@ defmodule Pleroma.Web.MastodonAPI.NotificationView do
 
     response = %{
       id: to_string(notification.id),
-      group_key: "ungrouped-" <> to_string(notification.id),
+      group_key: Notification.group_key(notification),
       type: notification.type,
       created_at: CommonAPI.Utils.to_masto_date(notification.inserted_at),
       account: account,
@@ -137,6 +189,104 @@ defmodule Pleroma.Web.MastodonAPI.NotificationView do
     Map.put(response, :report, report_render)
   end
 
+  defp render_group(
+         [%Notification{} = notification | _] = notifications,
+         _reading_user,
+         grouped_types,
+         notification_group_counts,
+         notification_group_bounds,
+         include_page_metadata
+       ) do
+    latest_notification = List.first(notifications)
+    oldest_notification = List.last(notifications)
+    status_activity = status_activity_for_group(notifications, grouped_types)
+    group_key = Notification.group_key(notification, grouped_types)
+    bounds = Map.get(notification_group_bounds, group_key, %{})
+
+    response = %{
+      group_key: group_key,
+      notifications_count: Map.get(notification_group_counts, group_key, length(notifications)),
+      type: notification.type,
+      most_recent_notification_id:
+        bounds
+        |> Map.get(:page_max_id, latest_notification.id)
+        |> to_string(),
+      sample_account_ids:
+        notifications
+        |> notification_actors()
+        |> Enum.map(&to_string(&1.id))
+    }
+
+    response =
+      if include_page_metadata do
+        Map.merge(response, %{
+          page_min_id:
+            bounds
+            |> Map.get(:page_min_id, oldest_notification.id)
+            |> to_string(),
+          page_max_id:
+            bounds
+            |> Map.get(:page_max_id, latest_notification.id)
+            |> to_string(),
+          latest_page_notification_at:
+            bounds
+            |> Map.get(:latest_page_notification_at, latest_notification.inserted_at)
+            |> CommonAPI.Utils.to_masto_date()
+        })
+      else
+        response
+      end
+
+    if status_activity do
+      Map.put(response, :status_id, to_string(status_activity.id))
+    else
+      response
+    end
+  end
+
+  defp status_activity_for_group([%Notification{} = notification | _], grouped_types) do
+    status_activity_for(notification, grouped_types)
+  end
+
+  defp status_activity_for(%Notification{type: type, activity: activity}, _grouped_types)
+       when type in ["mention", "status", "poll"] do
+    activity
+  end
+
+  defp status_activity_for(%Notification{type: type} = notification, grouped_types)
+       when type in ["favourite", "reblog"] do
+    group_key = Notification.group_key(notification, grouped_types)
+
+    case String.split(group_key, "-", parts: 3) do
+      [^type, activity_id, _bucket] ->
+        case Activity.create_by_id_with_object(activity_id) do
+          %Activity{} = activity -> activity
+          _ -> parent_status_activity(notification.activity)
+        end
+
+      _ ->
+        parent_status_activity(notification.activity)
+    end
+  end
+
+  defp status_activity_for(%Notification{type: type, activity: activity}, _grouped_types)
+       when type in ["update", "pleroma:emoji_reaction"] do
+    parent_status_activity(activity)
+  end
+
+  defp status_activity_for(_, _grouped_types), do: nil
+
+  defp parent_status_activity(activity) do
+    Activity.get_create_by_object_ap_id(object_id_for(activity))
+  end
+
+  defp notification_actors(notifications) do
+    notifications
+    |> Enum.map(&User.get_cached_by_ap_id(&1.activity.data["actor"]))
+    |> Enum.filter(& &1)
+    |> Enum.uniq_by(& &1.id)
+  end
+
   defp put_emoji(response, activity) do
     response
     |> Map.put(:emoji, activity.data["content"])

lib/pleroma/web/router.ex

@@ -844,6 +844,16 @@ defmodule Pleroma.Web.Router do
     get("/directory", DirectoryController, :index)
   end
 
+  scope "/api/v2", Pleroma.Web.MastodonAPI do
+    pipe_through(:authenticated_api)
+
+    get("/notifications", NotificationController, :grouped_index)
+    get("/notifications/unread_count", NotificationController, :unread_count)
+    get("/notifications/:group_key/accounts", NotificationController, :group_accounts)
+    get("/notifications/:group_key", NotificationController, :show_group)
+    post("/notifications/:group_key/dismiss", NotificationController, :dismiss_group)
+  end
+
   scope "/api/v2", Pleroma.Web.MastodonAPI do
     pipe_through(:api)
 

priv/repo/migrations/20200602125217_add_group_key_to_notifications.exs

@@ -0,0 +1,15 @@
+defmodule Pleroma.Repo.Migrations.AddGroupKeyToNotifications do
+  use Ecto.Migration
+
+  def change do
+    alter table(:notifications) do
+      add(:group_key, :string)
+    end
+
+    create_if_not_exists(
+      index(:notifications, [:user_id, :group_key, "id desc nulls last"],
+        where: "group_key IS NOT NULL"
+      )
+    )
+  end
+end

test/pleroma/web/mastodon_api/controllers/notification_controller_test.exs

@@ -577,6 +577,298 @@ defmodule Pleroma.Web.MastodonAPI.NotificationControllerTest do
     assert [%{"id" => ^notification4_id}, %{"id" => ^notification3_id}] = result
   end
 
+  describe "GET /api/v2/notifications" do
+    test "groups favourite notifications for the same status" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user1 = insert(:user)
+      other_user2 = insert(:user)
+
+      {:ok, status} = CommonAPI.post(user, %{status: "hello"})
+      {:ok, _} = CommonAPI.favorite(status.id, other_user1)
+      {:ok, _} = CommonAPI.favorite(status.id, other_user2)
+
+      notifications = Repo.all(Notification)
+      notification_ids = Enum.map(notifications, &to_string(&1.id))
+      assert [persisted_group_key] = notifications |> Enum.map(& &1.group_key) |> Enum.uniq()
+      assert is_binary(persisted_group_key)
+
+      result =
+        conn
+        |> get("/api/v2/notifications")
+        |> json_response_and_validate_schema(200)
+
+      assert [%{"id" => account_id1}, %{"id" => account_id2}] = result["accounts"]
+      assert account_id1 in [other_user1.id, other_user2.id]
+      assert account_id2 in [other_user1.id, other_user2.id]
+      assert [%{"id" => status_id}] = result["statuses"]
+      assert status_id == status.id
+
+      assert [group] = result["notification_groups"]
+      assert group["type"] == "favourite"
+      assert group["notifications_count"] == 2
+      assert group["status_id"] == status.id
+      assert group["most_recent_notification_id"] in notification_ids
+      assert group["page_min_id"] in notification_ids
+      assert group["page_max_id"] in notification_ids
+      assert group["latest_page_notification_at"]
+      assert Enum.sort(group["sample_account_ids"]) == Enum.sort([other_user1.id, other_user2.id])
+      group_key = group["group_key"]
+      assert group_key == persisted_group_key
+
+      assert [%{"group_key" => ^group_key}, %{"group_key" => ^group_key}] =
+               conn
+               |> get("/api/v1/notifications")
+               |> json_response_and_validate_schema(200)
+
+      assert %{"notification_groups" => [shown_group]} =
+               conn
+               |> get("/api/v2/notifications/#{group_key}")
+               |> json_response_and_validate_schema(200)
+
+      assert shown_group["group_key"] == group_key
+      assert shown_group["notifications_count"] == 2
+      refute Map.has_key?(shown_group, "page_min_id")
+      refute Map.has_key?(shown_group, "page_max_id")
+      refute Map.has_key?(shown_group, "latest_page_notification_at")
+    end
+
+    test "round-trips ungrouped group keys when grouped_types excludes a type" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user = insert(:user)
+
+      {:ok, status} = CommonAPI.post(user, %{status: "hello"})
+      {:ok, _} = CommonAPI.favorite(status.id, other_user)
+
+      %{"notification_groups" => [%{"group_key" => "ungrouped-" <> _ = group_key}]} =
+        conn
+        |> get("/api/v2/notifications?grouped_types[]=reblog")
+        |> json_response_and_validate_schema(200)
+
+      assert %{
+               "notification_groups" => [%{"group_key" => ^group_key, "notifications_count" => 1}]
+             } =
+               conn
+               |> get("/api/v2/notifications/#{group_key}")
+               |> json_response_and_validate_schema(200)
+    end
+
+    test "keeps legacy notifications without persisted group keys ungrouped" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user1 = insert(:user)
+      other_user2 = insert(:user)
+
+      {:ok, status} = CommonAPI.post(user, %{status: "hello"})
+      {:ok, favorite1} = CommonAPI.favorite(status.id, other_user1)
+      {:ok, favorite2} = CommonAPI.favorite(status.id, other_user2)
+
+      notification_ids =
+        [favorite1, favorite2]
+        |> Enum.map(&get_notification_id_by_activity/1)
+
+      Repo.update_all(Notification, set: [group_key: nil])
+
+      expected_group_keys = Enum.map(notification_ids, &"ungrouped-#{&1}")
+
+      assert [%{"group_key" => group_key1}, %{"group_key" => group_key2}] =
+               conn
+               |> get("/api/v1/notifications")
+               |> json_response_and_validate_schema(200)
+
+      assert Enum.sort([group_key1, group_key2]) == Enum.sort(expected_group_keys)
+
+      %{"notification_groups" => groups} =
+        conn
+        |> get("/api/v2/notifications")
+        |> json_response_and_validate_schema(200)
+
+      assert Enum.sort(Enum.map(groups, & &1["group_key"])) == Enum.sort(expected_group_keys)
+      assert Enum.all?(groups, &(&1["notifications_count"] == 1))
+
+      group_key = List.first(expected_group_keys)
+
+      assert %{
+               "notification_groups" => [%{"group_key" => ^group_key, "notifications_count" => 1}]
+             } =
+               conn
+               |> get("/api/v2/notifications/#{group_key}")
+               |> json_response_and_validate_schema(200)
+    end
+
+    test "paginates notification groups instead of raw notifications" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user1 = insert(:user)
+      other_user2 = insert(:user)
+      other_user3 = insert(:user)
+
+      {:ok, older_status} = CommonAPI.post(user, %{status: "older"})
+      {:ok, _} = CommonAPI.favorite(older_status.id, other_user3)
+
+      {:ok, newer_status} = CommonAPI.post(user, %{status: "newer"})
+      {:ok, _} = CommonAPI.favorite(newer_status.id, other_user1)
+      {:ok, _} = CommonAPI.favorite(newer_status.id, other_user2)
+      older_status_id = older_status.id
+      newer_status_id = newer_status.id
+
+      %{"notification_groups" => groups} =
+        conn
+        |> get("/api/v2/notifications?limit=2")
+        |> json_response_and_validate_schema(200)
+
+      assert [
+               %{"status_id" => ^newer_status_id, "notifications_count" => 2},
+               %{"status_id" => ^older_status_id, "notifications_count" => 1}
+             ] = groups
+    end
+
+    test "uses group-level cursors when paginating notification groups" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user1 = insert(:user)
+      other_user2 = insert(:user)
+      other_user3 = insert(:user)
+
+      {:ok, older_status} = CommonAPI.post(user, %{status: "older"})
+      {:ok, _} = CommonAPI.favorite(older_status.id, other_user3)
+
+      {:ok, newer_status} = CommonAPI.post(user, %{status: "newer"})
+      {:ok, _} = CommonAPI.favorite(newer_status.id, other_user1)
+      {:ok, _} = CommonAPI.favorite(newer_status.id, other_user2)
+      older_status_id = older_status.id
+      newer_status_id = newer_status.id
+
+      assert %{
+               "notification_groups" => [
+                 %{
+                   "status_id" => ^newer_status_id,
+                   "notifications_count" => 2,
+                   "most_recent_notification_id" => cursor
+                 }
+               ]
+             } =
+               conn
+               |> get("/api/v2/notifications?limit=1")
+               |> json_response_and_validate_schema(200)
+
+      assert %{
+               "notification_groups" => [
+                 %{"status_id" => ^older_status_id, "notifications_count" => 1}
+               ]
+             } =
+               conn
+               |> get("/api/v2/notifications?limit=1&max_id=#{cursor}")
+               |> json_response_and_validate_schema(200)
+    end
+
+    test "returns total notification count for a partially represented group" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user1 = insert(:user)
+      other_user2 = insert(:user)
+      other_user3 = insert(:user)
+
+      {:ok, grouped_status} = CommonAPI.post(user, %{status: "grouped"})
+      {:ok, _} = CommonAPI.favorite(grouped_status.id, other_user1)
+
+      {:ok, other_status} = CommonAPI.post(user, %{status: "other"})
+      {:ok, _} = CommonAPI.favorite(other_status.id, other_user3)
+      {:ok, _} = CommonAPI.favorite(grouped_status.id, other_user2)
+      grouped_status_id = grouped_status.id
+
+      assert %{
+               "notification_groups" => [
+                 %{"status_id" => ^grouped_status_id, "notifications_count" => 2}
+               ]
+             } =
+               conn
+               |> get("/api/v2/notifications?limit=1")
+               |> json_response_and_validate_schema(200)
+    end
+
+    test "counts unread notification groups" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user1 = insert(:user)
+      other_user2 = insert(:user)
+      mentioner = insert(:user)
+
+      {:ok, status} = CommonAPI.post(user, %{status: "hello"})
+      {:ok, _} = CommonAPI.favorite(status.id, other_user1)
+      {:ok, _} = CommonAPI.favorite(status.id, other_user2)
+      {:ok, _} = CommonAPI.post(mentioner, %{status: "hi @#{user.nickname}"})
+
+      assert %{"count" => 2} =
+               conn
+               |> get("/api/v2/notifications/unread_count")
+               |> json_response_and_validate_schema(200)
+    end
+
+    test "counts unread notification groups newer than the notification marker" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user = insert(:user)
+      mentioner = insert(:user)
+
+      {:ok, status} = CommonAPI.post(user, %{status: "older"})
+      {:ok, favorite_activity} = CommonAPI.favorite(status.id, other_user)
+      marker_id = get_notification_id_by_activity(favorite_activity)
+
+      {:ok, _} = CommonAPI.post(mentioner, %{status: "newer @#{user.nickname}"})
+
+      {:ok, _} =
+        Pleroma.Marker.upsert(user, %{"notifications" => %{"last_read_id" => marker_id}})
+
+      assert %{"count" => 1} =
+               conn
+               |> get("/api/v2/notifications/unread_count")
+               |> json_response_and_validate_schema(200)
+    end
+
+    test "does not preserve stale cursor params in grouped notification link headers" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+      other_user = insert(:user)
+
+      {:ok, activity1} = CommonAPI.post(other_user, %{status: "one @#{user.nickname}"})
+      {:ok, _activity2} = CommonAPI.post(other_user, %{status: "two @#{user.nickname}"})
+      {:ok, activity3} = CommonAPI.post(other_user, %{status: "three @#{user.nickname}"})
+
+      notification1_id = get_notification_id_by_activity(activity1)
+      notification3_id = get_notification_id_by_activity(activity3)
+
+      conn = get(conn, "/api/v2/notifications?since_id=#{notification1_id}&limit=1")
+
+      assert [link_header] = get_resp_header(conn, "link")
+      assert link_header =~ ~r/max_id=#{notification3_id}/
+      refute link_header =~ "since_id="
+    end
+
+    test "lists accounts from a notification group" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications"])
+
+      {other_users, %{"group_key" => group_key, "sample_account_ids" => sample_account_ids}} =
+        create_favourite_notification_group(user, conn)
+
+      assert length(sample_account_ids) == 8
+
+      account_ids =
+        conn
+        |> get("/api/v2/notifications/#{group_key}/accounts")
+        |> json_response_and_validate_schema(200)
+        |> Enum.map(& &1["id"])
+
+      assert Enum.sort(account_ids) == Enum.sort(Enum.map(other_users, & &1.id))
+    end
+
+    test "dismisses a notification group" do
+      %{user: user, conn: conn} = oauth_access(["read:notifications", "write:notifications"])
+
+      {_other_users, %{"group_key" => group_key}} =
+        create_favourite_notification_group(user, conn)
+
+      assert %{} =
+               conn
+               |> post("/api/v2/notifications/#{group_key}/dismiss")
+               |> json_response_and_validate_schema(200)
+
+      assert [] = Notification.for_user(user)
+    end
+  end
+
   test "doesn't see notifications after muting user with notifications" do
     %{user: user, conn: conn} = oauth_access(["read:notifications"])
     user2 = insert(:user)
@@ -708,6 +1000,29 @@ defmodule Pleroma.Web.MastodonAPI.NotificationControllerTest do
     |> to_string()
   end
 
+  defp create_favourite_notification_group(user, conn) do
+    other_users = insert_list(9, :user)
+
+    {:ok, status} = CommonAPI.post(user, %{status: "hello"})
+
+    Enum.each(other_users, fn other_user ->
+      {:ok, _} = CommonAPI.favorite(status.id, other_user)
+    end)
+
+    %{
+      "notification_groups" => [
+        %{
+          "notifications_count" => 9
+        } = group
+      ]
+    } =
+      conn
+      |> get("/api/v2/notifications")
+      |> json_response_and_validate_schema(200)
+
+    {other_users, group}
+  end
+
   defp params_to_query(%{} = params) do
     Enum.map_join(params, "&", fn
       {k, v} when is_list(v) -> Enum.map_join(v, "&", &"#{k}[]=#{&1}")

test/pleroma/web/mastodon_api/views/notification_view_test.exs

@@ -98,10 +98,11 @@ defmodule Pleroma.Web.MastodonAPI.NotificationViewTest do
     {:ok, favorite_activity} = CommonAPI.favorite(create_activity.id, another_user)
     {:ok, [notification]} = Notification.create_notifications(favorite_activity)
     create_activity = Activity.get_by_id(create_activity.id)
+    assert is_binary(notification.group_key)
 
     expected = %{
       id: to_string(notification.id),
-      group_key: "ungrouped-#{to_string(notification.id)}",
+      group_key: Notification.group_key(notification),
       pleroma: %{is_seen: false, is_muted: false},
       type: "favourite",
       account: AccountView.render("show.json", %{user: another_user, for: user}),
@@ -119,10 +120,11 @@ defmodule Pleroma.Web.MastodonAPI.NotificationViewTest do
     {:ok, reblog_activity} = CommonAPI.repeat(create_activity.id, another_user)
     {:ok, [notification]} = Notification.create_notifications(reblog_activity)
     reblog_activity = Activity.get_by_id(create_activity.id)
+    assert is_binary(notification.group_key)
 
     expected = %{
       id: to_string(notification.id),
-      group_key: "ungrouped-#{to_string(notification.id)}",
+      group_key: Notification.group_key(notification),
       pleroma: %{is_seen: false, is_muted: false},
       type: "reblog",
       account: AccountView.render("show.json", %{user: another_user, for: user}),
@@ -138,10 +140,11 @@ defmodule Pleroma.Web.MastodonAPI.NotificationViewTest do
     followed = insert(:user)
     {:ok, followed, follower, _activity} = CommonAPI.follow(followed, follower)
     notification = Notification |> Repo.one() |> Repo.preload(:activity)
+    assert is_binary(notification.group_key)
 
     expected = %{
       id: to_string(notification.id),
-      group_key: "ungrouped-#{to_string(notification.id)}",
+      group_key: Notification.group_key(notification),
       pleroma: %{is_seen: false, is_muted: false},
       type: "follow",
       account: AccountView.render("show.json", %{user: follower, for: followed}),
@@ -333,7 +336,7 @@ defmodule Pleroma.Web.MastodonAPI.NotificationViewTest do
 
     expected = %{
       id: to_string(notification.id),
-      group_key: "ungrouped-#{to_string(notification.id)}",
+      group_key: Notification.group_key(notification),
       pleroma: %{is_seen: true, is_muted: true},
       type: "favourite",
       account: AccountView.render("show.json", %{user: another_user, for: user}),