254 lines
8.1 KiB
Ruby
254 lines
8.1 KiB
Ruby
# frozen_string_literal: true
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module Gitlab
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module RelativePositioning
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# This class is API private - it should not be explicitly instantiated
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# outside of tests
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# rubocop: disable CodeReuse/ActiveRecord
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class ItemContext
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include Gitlab::Utils::StrongMemoize
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attr_reader :object, :model_class, :range
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attr_accessor :ignoring
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def initialize(object, range, ignoring: nil)
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@object = object
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@range = range
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@model_class = object.class
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@ignoring = ignoring
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end
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def ==(other)
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other.is_a?(self.class) && other.object == object && other.range == range && other.ignoring == ignoring
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end
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def positioned?
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relative_position.present?
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end
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def min_relative_position
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strong_memoize(:min_relative_position) { calculate_relative_position('MIN') }
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end
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def max_relative_position
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strong_memoize(:max_relative_position) { calculate_relative_position('MAX') }
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end
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def prev_relative_position
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calculate_relative_position('MAX') { |r| nextify(r, false) } if object.relative_position
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end
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def next_relative_position
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calculate_relative_position('MIN') { |r| nextify(r) } if object.relative_position
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end
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def nextify(relation, gt = true)
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if gt
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relation.where("relative_position > ?", relative_position)
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else
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relation.where("relative_position < ?", relative_position)
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end
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end
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def relative_siblings(relation = scoped_items)
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object.exclude_self(relation)
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end
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# Handles the possibility that the position is already occupied by a sibling
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def place_at_position(position, lhs)
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current_occupant = relative_siblings.find_by(relative_position: position)
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if current_occupant.present?
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Mover.new(position, range).move(object, lhs.object, current_occupant)
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else
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object.relative_position = position
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end
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end
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def lhs_neighbour
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neighbour(object.next_object_by_relative_position(ignoring: ignoring, order: :desc))
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end
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def rhs_neighbour
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neighbour(object.next_object_by_relative_position(ignoring: ignoring, order: :asc))
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end
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def neighbour(item)
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return unless item.present?
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self.class.new(item, range, ignoring: ignoring)
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end
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def calculate_relative_position(calculation)
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# When calculating across projects, this is much more efficient than
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# MAX(relative_position) without the GROUP BY, due to index usage:
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# https://gitlab.com/gitlab-org/gitlab-foss/issues/54276#note_119340977
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relation = scoped_items
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.order(Arel.sql('position').desc.nulls_last)
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.group(grouping_column)
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.limit(1)
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relation = yield relation if block_given?
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relation
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.pick(grouping_column, Arel.sql("#{calculation}(relative_position) AS position"))&.last
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end
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def grouping_column
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model_class.relative_positioning_parent_column
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end
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def max_sibling
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sib = relative_siblings
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.order(model_class.arel_table[:relative_position].desc.nulls_last)
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.first
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neighbour(sib)
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end
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def min_sibling
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sib = relative_siblings
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.order(model_class.arel_table[:relative_position].asc.nulls_last)
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.first
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neighbour(sib)
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end
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def at_position(position)
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item = scoped_items.find_by(relative_position: position)
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raise InvalidPosition, 'No item found at the specified position' if item.nil?
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neighbour(item)
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end
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def shift_left
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move_sequence_before(true)
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object.reset_relative_position
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end
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def shift_right
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move_sequence_after(true)
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object.reset_relative_position
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end
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def create_space_left
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find_next_gap_before.tap { |gap| move_sequence_before(false, next_gap: gap) }
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end
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def create_space_right
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find_next_gap_after.tap { |gap| move_sequence_after(false, next_gap: gap) }
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end
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def find_next_gap_before
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items_with_next_pos = scoped_items
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.select('relative_position AS pos, LEAD(relative_position) OVER (ORDER BY relative_position DESC) AS next_pos')
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.where('relative_position <= ?', relative_position)
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.order(relative_position: :desc)
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find_next_gap(items_with_next_pos, range.first)
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end
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def find_next_gap_after
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items_with_next_pos = scoped_items
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.select('relative_position AS pos, LEAD(relative_position) OVER (ORDER BY relative_position ASC) AS next_pos')
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.where('relative_position >= ?', relative_position)
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.order(:relative_position)
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find_next_gap(items_with_next_pos, range.last)
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end
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def find_next_gap(items_with_next_pos, default_end)
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gap = model_class
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.from(items_with_next_pos, :items)
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.where('next_pos IS NULL OR ABS(pos::bigint - next_pos::bigint) >= ?', MIN_GAP)
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.pick(:pos, :next_pos)
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return if gap.nil? || gap.first == default_end
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Gap.new(gap.first, gap.second || default_end)
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end
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def scoped_items
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object.relative_positioning_scoped_items(ignoring: ignoring)
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end
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def relative_position
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object.relative_position
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end
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private
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# Moves the sequence before the current item to the middle of the next gap
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# For example, we have
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#
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# 5 . . . . . 11 12 13 14 [15] 16 . 17
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# -----------
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#
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# This moves the sequence [11 12 13 14] to [8 9 10 11], so we have:
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#
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# 5 . . 8 9 10 11 . . . [15] 16 . 17
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# ---------
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#
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# Creating a gap to the left of the current item. We can understand this as
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# dividing the 5 spaces between 5 and 11 into two smaller gaps of 2 and 3.
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#
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# If `include_self` is true, the current item will also be moved, creating a
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# gap to the right of the current item:
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#
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# 5 . . 8 9 10 11 [14] . . . 16 . 17
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# --------------
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#
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# As an optimization, the gap can be precalculated and passed to this method.
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#
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# @api private
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# @raises NoSpaceLeft if the sequence cannot be moved
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def move_sequence_before(include_self = false, next_gap: find_next_gap_before)
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raise NoSpaceLeft unless next_gap.present?
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delta = next_gap.delta
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move_sequence(next_gap.start_pos, relative_position, -delta, include_self)
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end
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# Moves the sequence after the current item to the middle of the next gap
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# For example, we have:
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#
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# 8 . 10 [11] 12 13 14 15 . . . . . 21
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# -----------
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#
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# This moves the sequence [12 13 14 15] to [15 16 17 18], so we have:
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#
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# 8 . 10 [11] . . . 15 16 17 18 . . 21
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# -----------
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#
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# Creating a gap to the right of the current item. We can understand this as
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# dividing the 5 spaces between 15 and 21 into two smaller gaps of 3 and 2.
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#
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# If `include_self` is true, the current item will also be moved, creating a
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# gap to the left of the current item:
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#
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# 8 . 10 . . . [14] 15 16 17 18 . . 21
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# ----------------
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#
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# As an optimization, the gap can be precalculated and passed to this method.
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#
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# @api private
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# @raises NoSpaceLeft if the sequence cannot be moved
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def move_sequence_after(include_self = false, next_gap: find_next_gap_after)
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raise NoSpaceLeft unless next_gap.present?
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delta = next_gap.delta
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move_sequence(relative_position, next_gap.start_pos, delta, include_self)
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end
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def move_sequence(start_pos, end_pos, delta, include_self = false)
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relation = include_self ? scoped_items : relative_siblings
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object.update_relative_siblings(relation, (start_pos..end_pos), delta)
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end
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end
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# rubocop: enable CodeReuse/ActiveRecord
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end
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end
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