# Pleroma: A lightweight social networking server # Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/> # SPDX-License-Identifier: AGPL-3.0-only defmodule Pleroma.Pagination do @moduledoc """ Implements Mastodon-compatible pagination. """ import Ecto.Query import Ecto.Changeset alias Pleroma.Repo @type type :: :keyset | :offset @default_limit 20 @max_limit 40 @page_keys ["max_id", "min_id", "limit", "since_id", "order"] def page_keys, do: @page_keys @spec fetch_paginated(Ecto.Query.t(), map(), type(), atom() | nil) :: [Ecto.Schema.t()] def fetch_paginated(query, params, type \\ :keyset, table_binding \\ nil) def fetch_paginated(query, %{total: true} = params, :keyset, table_binding) do total = Repo.aggregate(query, :count, :id) %{ total: total, items: fetch_paginated(query, Map.drop(params, [:total]), :keyset, table_binding) } end def fetch_paginated(query, params, :keyset, table_binding) do options = cast_params(params) query |> paginate(options, :keyset, table_binding) |> Repo.all() |> enforce_order(options) end def fetch_paginated(query, %{total: true} = params, :offset, table_binding) do total = query |> Ecto.Query.exclude(:left_join) |> Repo.aggregate(:count, :id) %{ total: total, items: fetch_paginated(query, Map.drop(params, [:total]), :offset, table_binding) } end def fetch_paginated(query, params, :offset, table_binding) do options = cast_params(params) query |> paginate(options, :offset, table_binding) |> Repo.all() end @spec paginate(Ecto.Query.t(), map(), type(), atom() | nil) :: [Ecto.Schema.t()] def paginate(query, options, method \\ :keyset, table_binding \\ nil) def paginate(list, options, _method, _table_binding) when is_list(list) do offset = options[:offset] || 0 limit = options[:limit] || 0 Enum.slice(list, offset, limit) end def paginate(query, options, :keyset, table_binding) do query |> restrict(:min_id, options, table_binding) |> restrict(:since_id, options, table_binding) |> restrict(:max_id, options, table_binding) |> restrict(:order, options, table_binding) |> restrict(:limit, options, table_binding) end def paginate(query, options, :offset, table_binding) do query |> restrict(:order, options, table_binding) |> restrict(:offset, options, table_binding) |> restrict(:limit, options, table_binding) end defp cast_params(params) do param_types = %{ min_id: :string, since_id: :string, max_id: :string, offset: :integer, limit: :integer, skip_order: :boolean } changeset = cast({%{}, param_types}, params, Map.keys(param_types)) changeset.changes end defp restrict(query, :min_id, %{min_id: min_id}, table_binding) do where(query, [{q, table_position(query, table_binding)}], q.id > ^min_id) end defp restrict(query, :since_id, %{since_id: since_id}, table_binding) do where(query, [{q, table_position(query, table_binding)}], q.id > ^since_id) end defp restrict(query, :max_id, %{max_id: max_id}, table_binding) do where(query, [{q, table_position(query, table_binding)}], q.id < ^max_id) end defp restrict(query, :order, %{skip_order: true}, _), do: query defp restrict(query, :order, %{min_id: _}, table_binding) do order_by( query, [{u, table_position(query, table_binding)}], fragment("? asc nulls last", u.id) ) end defp restrict(query, :order, _options, table_binding) do order_by( query, [{u, table_position(query, table_binding)}], fragment("? desc nulls last", u.id) ) end defp restrict(query, :offset, %{offset: offset}, _table_binding) do offset(query, ^offset) end defp restrict(query, :limit, options, _table_binding) do limit = case Map.get(options, :limit, @default_limit) do limit when limit < @max_limit -> limit _ -> @max_limit end query |> limit(^limit) end defp restrict(query, _, _, _), do: query defp enforce_order(result, %{min_id: _}) do result |> Enum.reverse() end defp enforce_order(result, _), do: result defp table_position(%Ecto.Query{} = query, binding_name) do Map.get(query.aliases, binding_name, 0) end defp table_position(_, _), do: 0 end