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|
# frozen_string_literal: true
module Gitlab
module Pagination
module Keyset
class Paginator
include Enumerable
module Base64CursorConverter
def self.dump(cursor_attributes)
Base64.urlsafe_encode64(Gitlab::Json.dump(cursor_attributes))
end
def self.parse(cursor)
Gitlab::Json.parse(Base64.urlsafe_decode64(cursor)).with_indifferent_access
end
end
FORWARD_DIRECTION = 'n'
BACKWARD_DIRECTION = 'p'
UnsupportedScopeOrder = Class.new(StandardError)
# scope - ActiveRecord::Relation object with order by clause
# cursor - Encoded cursor attributes as String. Empty value will requests the first page.
# per_page - Number of items per page.
# cursor_converter - Object that serializes and de-serializes the cursor attributes. Implements dump and parse methods.
# direction_key - Symbol that will be the hash key of the direction within the cursor. (default: _kd => keyset direction)
def initialize(scope:, cursor: nil, per_page: 20, cursor_converter: Base64CursorConverter, direction_key: :_kd)
@keyset_scope = build_scope(scope)
@order = Gitlab::Pagination::Keyset::Order.extract_keyset_order_object(@keyset_scope)
@per_page = per_page
@cursor_converter = cursor_converter
@direction_key = direction_key
@has_another_page = false
@at_last_page = false
@at_first_page = false
@cursor_attributes = decode_cursor_attributes(cursor)
set_pagination_helper_flags!
end
# rubocop: disable CodeReuse/ActiveRecord
def records
@records ||= begin
items = if paginate_backward?
reversed_order
.apply_cursor_conditions(keyset_scope, cursor_attributes)
.reorder(reversed_order)
.limit(per_page_plus_one)
.to_a
else
order
.apply_cursor_conditions(keyset_scope, cursor_attributes)
.limit(per_page_plus_one)
.to_a
end
@has_another_page = items.size == per_page_plus_one
items.pop if @has_another_page
items.reverse! if paginate_backward?
items
end
end
# rubocop: enable CodeReuse/ActiveRecord
# This and has_previous_page? methods are direction aware. In case we paginate backwards,
# has_next_page? will mean that we have a previous page.
def has_next_page?
records
if at_last_page?
false
elsif paginate_forward?
@has_another_page
elsif paginate_backward?
true
end
end
def has_previous_page?
records
if at_first_page?
false
elsif paginate_backward?
@has_another_page
elsif paginate_forward?
true
end
end
def cursor_for_next_page
if has_next_page?
data = order.cursor_attributes_for_node(records.last)
data[direction_key] = FORWARD_DIRECTION
cursor_converter.dump(data)
else
nil
end
end
def cursor_for_previous_page
if has_previous_page?
data = order.cursor_attributes_for_node(records.first)
data[direction_key] = BACKWARD_DIRECTION
cursor_converter.dump(data)
end
end
def cursor_for_first_page
cursor_converter.dump({ direction_key => FORWARD_DIRECTION })
end
def cursor_for_last_page
cursor_converter.dump({ direction_key => BACKWARD_DIRECTION })
end
delegate :each, :empty?, :any?, to: :records
private
attr_reader :keyset_scope, :order, :per_page, :cursor_converter, :direction_key, :cursor_attributes
delegate :reversed_order, to: :order
def at_last_page?
@at_last_page
end
def at_first_page?
@at_first_page
end
def per_page_plus_one
per_page + 1
end
def decode_cursor_attributes(cursor)
cursor.blank? ? {} : cursor_converter.parse(cursor)
end
def set_pagination_helper_flags!
@direction = cursor_attributes.delete(direction_key.to_s)
if cursor_attributes.blank? && @direction.blank?
@at_first_page = true
@direction = FORWARD_DIRECTION
elsif cursor_attributes.blank?
if paginate_forward?
@at_first_page = true
else
@at_last_page = true
end
end
end
def paginate_backward?
@direction == BACKWARD_DIRECTION
end
def paginate_forward?
@direction == FORWARD_DIRECTION
end
def build_scope(scope)
keyset_aware_scope, success = Gitlab::Pagination::Keyset::SimpleOrderBuilder.build(scope)
raise(UnsupportedScopeOrder, 'The order on the scope does not support keyset pagination') unless success
keyset_aware_scope
end
end
end
end
end
|
