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# Pleroma: A lightweight social networking server
# Copyright © 2017-2022 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_list(list(), keyword()) :: list()
def paginate_list(list, options) do
offset = options[:offset] || 0
limit = options[:limit] || 0
Enum.slice(list, offset, limit)
end
@spec paginate(Ecto.Query.t(), map(), type(), atom() | nil) :: [Ecto.Schema.t()]
def paginate(query, options, method \\ :keyset, table_binding \\ nil)
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_extra_order: :boolean,
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(%{order_bys: [_ | _]} = query, :order, %{skip_extra_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

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