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   1 # Pleroma: A lightweight social networking server
   2 # Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
   3 # SPDX-License-Identifier: AGPL-3.0-only
   4
   5 defmodule Pleroma.Pagination do
   6   @moduledoc """
   7   Implements Mastodon-compatible pagination.
   8   """
   9
  10   import Ecto.Query
  11   import Ecto.Changeset
  12
  13   alias Pleroma.Repo
  14
  15   @type type :: :keyset | :offset
  16
  17   @default_limit 20
  18   @max_limit 40
  19   @page_keys ["max_id", "min_id", "limit", "since_id", "order"]
  20
  21   def page_keys, do: @page_keys
  22
  23   @spec fetch_paginated(Ecto.Query.t(), map(), type(), atom() | nil) :: [Ecto.Schema.t()]
  24   def fetch_paginated(query, params, type \\ :keyset, table_binding \\ nil)
  25
  26   def fetch_paginated(query, %{total: true} = params, :keyset, table_binding) do
  27     total = Repo.aggregate(query, :count, :id)
  28
  29     %{
  30       total: total,
  31       items: fetch_paginated(query, Map.drop(params, [:total]), :keyset, table_binding)
  32     }
  33   end
  34
  35   def fetch_paginated(query, params, :keyset, table_binding) do
  36     options = cast_params(params)
  37
  38     query
  39     |> paginate(options, :keyset, table_binding)
  40     |> Repo.all()
  41     |> enforce_order(options)
  42   end
  43
  44   def fetch_paginated(query, %{total: true} = params, :offset, table_binding) do
  45     total =
  46       query
  47       |> Ecto.Query.exclude(:left_join)
  48       |> Repo.aggregate(:count, :id)
  49
  50     %{
  51       total: total,
  52       items: fetch_paginated(query, Map.drop(params, [:total]), :offset, table_binding)
  53     }
  54   end
  55
  56   def fetch_paginated(query, params, :offset, table_binding) do
  57     options = cast_params(params)
  58
  59     query
  60     |> paginate(options, :offset, table_binding)
  61     |> Repo.all()
  62   end
  63
  64   @spec paginate(Ecto.Query.t(), map(), type(), atom() | nil) :: [Ecto.Schema.t()]
  65   def paginate(query, options, method \\ :keyset, table_binding \\ nil)
  66
  67   def paginate(list, options, _method, _table_binding) when is_list(list) do
  68     offset = options[:offset] || 0
  69     limit = options[:limit] || 0
  70     Enum.slice(list, offset, limit)
  71   end
  72
  73   def paginate(query, options, :keyset, table_binding) do
  74     query
  75     |> restrict(:min_id, options, table_binding)
  76     |> restrict(:since_id, options, table_binding)
  77     |> restrict(:max_id, options, table_binding)
  78     |> restrict(:order, options, table_binding)
  79     |> restrict(:limit, options, table_binding)
  80   end
  81
  82   def paginate(query, options, :offset, table_binding) do
  83     query
  84     |> restrict(:order, options, table_binding)
  85     |> restrict(:offset, options, table_binding)
  86     |> restrict(:limit, options, table_binding)
  87   end
  88
  89   defp cast_params(params) do
  90     param_types = %{
  91       min_id: :string,
  92       since_id: :string,
  93       max_id: :string,
  94       offset: :integer,
  95       limit: :integer,
  96       skip_extra_order: :boolean,
  97       skip_order: :boolean
  98     }
  99
 100     changeset = cast({%{}, param_types}, params, Map.keys(param_types))
 101     changeset.changes
 102   end
 103
 104   defp restrict(query, :min_id, %{min_id: min_id}, table_binding) do
 105     where(query, [{q, table_position(query, table_binding)}], q.id > ^min_id)
 106   end
 107
 108   defp restrict(query, :since_id, %{since_id: since_id}, table_binding) do
 109     where(query, [{q, table_position(query, table_binding)}], q.id > ^since_id)
 110   end
 111
 112   defp restrict(query, :max_id, %{max_id: max_id}, table_binding) do
 113     where(query, [{q, table_position(query, table_binding)}], q.id < ^max_id)
 114   end
 115
 116   defp restrict(query, :order, %{skip_order: true}, _), do: query
 117
 118   defp restrict(%{order_bys: [_ | _]} = query, :order, %{skip_extra_order: true}, _), do: query
 119
 120   defp restrict(query, :order, %{min_id: _}, table_binding) do
 121     order_by(
 122       query,
 123       [{u, table_position(query, table_binding)}],
 124       fragment("? asc nulls last", u.id)
 125     )
 126   end
 127
 128   defp restrict(query, :order, _options, table_binding) do
 129     order_by(
 130       query,
 131       [{u, table_position(query, table_binding)}],
 132       fragment("? desc nulls last", u.id)
 133     )
 134   end
 135
 136   defp restrict(query, :offset, %{offset: offset}, _table_binding) do
 137     offset(query, ^offset)
 138   end
 139
 140   defp restrict(query, :limit, options, _table_binding) do
 141     limit =
 142       case Map.get(options, :limit, @default_limit) do
 143         limit when limit < @max_limit -> limit
 144         _ -> @max_limit
 145       end
 146
 147     query
 148     |> limit(^limit)
 149   end
 150
 151   defp restrict(query, _, _, _), do: query
 152
 153   defp enforce_order(result, %{min_id: _}) do
 154     result
 155     |> Enum.reverse()
 156   end
 157
 158   defp enforce_order(result, _), do: result
 159
 160   defp table_position(%Ecto.Query{} = query, binding_name) do
 161     Map.get(query.aliases, binding_name, 0)
 162   end
 163
 164   defp table_position(_, _), do: 0
 165 end