defmodule Pleroma.Pagination do @moduledoc """ Implements Mastodon-compatible pagination. """ import Ecto.Query import Ecto.Changeset alias Pleroma.Repo @default_limit 20 def fetch_paginated(query, params) do options = cast_params(params) query |> paginate(options) |> Repo.all() |> enforce_order(options) end def paginate(query, options) do query |> restrict(:min_id, options) |> restrict(:since_id, options) |> restrict(:max_id, options) |> restrict(:order, options) |> restrict(:limit, options) end defp cast_params(params) do param_types = %{ min_id: :string, since_id: :string, max_id: :string, limit: :integer } changeset = cast({%{}, param_types}, params, Map.keys(param_types)) changeset.changes end defp restrict(query, :min_id, %{min_id: min_id}) do where(query, [q], q.id > ^min_id) end defp restrict(query, :since_id, %{since_id: since_id}) do where(query, [q], q.id > ^since_id) end defp restrict(query, :max_id, %{max_id: max_id}) do where(query, [q], q.id < ^max_id) end defp restrict(query, :order, %{min_id: _}) do order_by(query, [u], fragment("? asc nulls last", u.id)) end defp restrict(query, :order, _options) do order_by(query, [u], fragment("? desc nulls last", u.id)) end defp restrict(query, :limit, options) do limit = Map.get(options, :limit, @default_limit) 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 end