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Commit ccec75e5 authored by Alex Kalderimis's avatar Alex Kalderimis
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Move relative_positioning helper classes into lib/ 

This moves Mover, ItemContext and Gap into the lib tree where they can
be used separately from the app code.
parent 363e8f13
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app/models/concerns/relative_positioning.rb
View file @ ccec75e5
......@@ -26,432 +26,8 @@
# end
#
module RelativePositioning
class Gap
attr_reader :start_pos, :end_pos
def initialize(start_pos, end_pos)
@start_pos, @end_pos = start_pos, end_pos
end
def ==(other)
other.is_a?(self.class) && other.start_pos == start_pos && other.end_pos == end_pos
end
def delta
((start_pos - end_pos) / 2.0).abs.ceil.clamp(0, RelativePositioning::IDEAL_DISTANCE)
end
end
# This class is API private - it should not be explicitly instantiated
# outside of tests
class ItemContext
include Gitlab::Utils::StrongMemoize
attr_reader :object, :model_class, :range
attr_accessor :ignoring
def initialize(object, range)
@object = object
@range = range
@model_class = object.class
end
def min_relative_position
strong_memoize(:min_relative_position) { calculate_relative_position('MIN') }
end
def max_relative_position
strong_memoize(:max_relative_position) { calculate_relative_position('MAX') }
end
def prev_relative_position
calculate_relative_position('MAX') { |r| nextify(r, false) } if object.relative_position
end
def next_relative_position
calculate_relative_position('MIN') { |r| nextify(r) } if object.relative_position
end
def nextify(relation, gt = true)
if gt
relation.where("relative_position > ?", relative_position)
else
relation.where("relative_position < ?", relative_position)
end
end
def relative_siblings(relation = scoped_items)
object.exclude_self(relation)
end
# Handles the possibility that the position is already occupied by a sibling
def place_at_position(position, lhs)
current_occupant = relative_siblings.find_by(relative_position: position)
if current_occupant.present?
Mover.new(position, range).move(object, lhs.object, current_occupant)
else
object.relative_position = position
end
end
def lhs_neighbour
scoped_items
.where('relative_position < ?', relative_position)
.reorder(relative_position: :desc)
.first
.then { |x| neighbour(x) }
end
def rhs_neighbour
scoped_items
.where('relative_position > ?', relative_position)
.reorder(relative_position: :asc)
.first
.then { |x| neighbour(x) }
end
def neighbour(item)
return unless item.present?
n = self.class.new(item, range)
n.ignoring = ignoring
n
end
def scoped_items
r = model_class.relative_positioning_query_base(object)
r = object.exclude_self(r, excluded: ignoring) if ignoring.present?
r
end
def calculate_relative_position(calculation)
# When calculating across projects, this is much more efficient than
# MAX(relative_position) without the GROUP BY, due to index usage:
# https://gitlab.com/gitlab-org/gitlab-foss/issues/54276#note_119340977
relation = scoped_items
.order(Gitlab::Database.nulls_last_order('position', 'DESC'))
.group(grouping_column)
.limit(1)
relation = yield relation if block_given?
relation
.pluck(grouping_column, Arel.sql("#{calculation}(relative_position) AS position"))
.first&.last
end
def grouping_column
model_class.relative_positioning_parent_column
end
def max_sibling
sib = relative_siblings
.order(Gitlab::Database.nulls_last_order('relative_position', 'DESC'))
.first
self.class.new(sib, range)
end
def min_sibling
sib = relative_siblings
.order(Gitlab::Database.nulls_last_order('relative_position', 'ASC'))
.first
self.class.new(sib, range)
end
def shift_left
move_sequence_before(true)
object.reset
end
def shift_right
move_sequence_after(true)
object.reset
end
def create_space_left
find_next_gap_before.tap { |gap| move_sequence_before(false, next_gap: gap) }
end
def create_space_right
find_next_gap_after.tap { |gap| move_sequence_after(false, next_gap: gap) }
end
# Moves the sequence before the current item to the middle of the next gap
# For example, we have
#
# 5 . . . . . 11 12 13 14 [15] 16 . 17
# -----------
#
# This moves the sequence [11 12 13 14] to [8 9 10 11], so we have:
#
# 5 . . 8 9 10 11 . . . [15] 16 . 17
# ---------
#
# Creating a gap to the left of the current item. We can understand this as
# dividing the 5 spaces between 5 and 11 into two smaller gaps of 2 and 3.
#
# If `include_self` is true, the current item will also be moved, creating a
# gap to the right of the current item:
#
# 5 . . 8 9 10 11 [14] . . . 16 . 17
# --------------
#
# As an optimization, the gap can be precalculated and passed to this method.
#
# @api private
# @raises NoSpaceLeft if the sequence cannot be moved
def move_sequence_before(include_self = false, next_gap: find_next_gap_before)
raise NoSpaceLeft unless next_gap.present?
delta = next_gap.delta
move_sequence(next_gap.start_pos, relative_position, -delta, include_self)
end
# Moves the sequence after the current item to the middle of the next gap
# For example, we have:
#
# 8 . 10 [11] 12 13 14 15 . . . . . 21
# -----------
#
# This moves the sequence [12 13 14 15] to [15 16 17 18], so we have:
#
# 8 . 10 [11] . . . 15 16 17 18 . . 21
# -----------
#
# Creating a gap to the right of the current item. We can understand this as
# dividing the 5 spaces between 15 and 21 into two smaller gaps of 3 and 2.
#
# If `include_self` is true, the current item will also be moved, creating a
# gap to the left of the current item:
#
# 8 . 10 . . . [14] 15 16 17 18 . . 21
# ----------------
#
# As an optimization, the gap can be precalculated and passed to this method.
#
# @api private
# @raises NoSpaceLeft if the sequence cannot be moved
def move_sequence_after(include_self = false, next_gap: find_next_gap_after)
raise NoSpaceLeft unless next_gap.present?
delta = next_gap.delta
move_sequence(relative_position, next_gap.start_pos, delta, include_self)
end
def move_sequence(start_pos, end_pos, delta, include_self = false)
relation = include_self ? scoped_items : relative_siblings
object.update_relative_siblings(relation, (start_pos..end_pos), delta)
end
def find_next_gap_before
items_with_next_pos = scoped_items
.select('relative_position AS pos, LEAD(relative_position) OVER (ORDER BY relative_position DESC) AS next_pos')
.where('relative_position <= ?', relative_position)
.order(relative_position: :desc)
find_next_gap(items_with_next_pos, range.first)
end
def find_next_gap_after
items_with_next_pos = scoped_items
.select('relative_position AS pos, LEAD(relative_position) OVER (ORDER BY relative_position ASC) AS next_pos')
.where('relative_position >= ?', relative_position)
.order(:relative_position)
find_next_gap(items_with_next_pos, range.last)
end
def find_next_gap(items_with_next_pos, default_end)
gap = model_class
.from(items_with_next_pos, :items)
.where('next_pos IS NULL OR ABS(pos::bigint - next_pos::bigint) >= ?', RelativePositioning::MIN_GAP)
.limit(1)
.pluck(:pos, :next_pos)
.first
return if gap.nil? || gap.first == default_end
Gap.new(gap.first, gap.second || default_end)
end
def relative_position
object.relative_position
end
end
class Mover
attr_reader :range, :start_position
def initialize(start, range)
@range = range
@start_position = start
end
def move_to_end(object)
focus = context(object, ignoring: object)
max_pos = focus.max_relative_position
move_to_range_end(focus, max_pos)
end
def move_to_start(object)
focus = context(object, ignoring: object)
min_pos = focus.min_relative_position
move_to_range_start(focus, min_pos)
end
def move(object, first, last)
raise ArgumentError unless object && (first || last) && (first != last)
# Moving a object next to itself is a no-op
return if object == first || object == last
lhs = context(first, ignoring: object)
rhs = context(last, ignoring: object)
focus = context(object)
lhs ||= rhs.lhs_neighbour
rhs ||= lhs.rhs_neighbour
if lhs.nil?
move_to_range_start(focus, rhs.relative_position)
elsif rhs.nil?
move_to_range_end(focus, lhs.relative_position)
else
pos_left, pos_right = create_space_between(lhs, rhs)
desired_position = position_between(pos_left, pos_right)
focus.place_at_position(desired_position, lhs)
end
end
def context(object, ignoring: nil)
return unless object
c = ItemContext.new(object, range)
c.ignoring = ignoring
c
end
private
def gap_too_small?(pos_a, pos_b)
return false unless pos_a && pos_b
(pos_a - pos_b).abs < MIN_GAP
end
def move_to_range_end(context, max_pos)
range_end = range.last + 1
new_pos = if max_pos.nil?
start_position
elsif gap_too_small?(max_pos, range_end)
max = context.max_sibling
max.ignoring = context.object
max.shift_left
position_between(max.relative_position, range_end)
else
position_between(max_pos, range_end)
end
context.object.relative_position = new_pos
end
def move_to_range_start(context, min_pos)
range_end = range.first - 1
new_pos = if min_pos.nil?
start_position
elsif gap_too_small?(min_pos, range_end)
sib = context.min_sibling
sib.ignoring = context.object
sib.shift_right
position_between(sib.relative_position, range_end)
else
position_between(min_pos, range_end)
end
context.object.relative_position = new_pos
end
def create_space_between(lhs, rhs)
pos_left = lhs&.relative_position
pos_right = rhs&.relative_position
return [pos_left, pos_right] unless gap_too_small?(pos_left, pos_right)
gap = rhs.create_space_left
[pos_left - gap.delta, pos_right]
rescue NoSpaceLeft
gap = lhs.create_space_right
[pos_left, pos_right + gap.delta]
end
# This method takes two integer values (positions) and
# calculates the position between them. The range is huge as
# the maximum integer value is 2147483647.
#
# We avoid open ranges by clamping the range to [MIN_POSITION, MAX_POSITION].
#
# Then we handle one of three cases:
# - If the gap is too small, we raise NoSpaceLeft
# - If the gap is larger than MAX_GAP, we place the new position at most
# IDEAL_DISTANCE from the edge of the gap.
# - otherwise we place the new position at the midpoint.
#
# The new position will always satisfy: pos_before <= midpoint <= pos_after
#
# As a precondition, the gap between pos_before and pos_after MUST be >= 2.
# If the gap is too small, NoSpaceLeft is raised.
#
# @raises NoSpaceLeft
def position_between(pos_before, pos_after)
pos_before ||= range.first
pos_after ||= range.last
pos_before, pos_after = [pos_before, pos_after].sort
gap_width = pos_after - pos_before
if gap_too_small?(pos_before, pos_after)
raise RelativePositioning::NoSpaceLeft
elsif gap_width > RelativePositioning::MAX_GAP
if pos_before <= range.first
pos_after - RelativePositioning::IDEAL_DISTANCE
elsif pos_after >= range.last
pos_before + RelativePositioning::IDEAL_DISTANCE
else
midpoint(pos_before, pos_after)
end
else
midpoint(pos_before, pos_after)
end
end
def midpoint(lower_bound, upper_bound)
((lower_bound + upper_bound) / 2.0).ceil.clamp(lower_bound, upper_bound - 1)
end
end
extend ActiveSupport::Concern
STEPS = 10
IDEAL_DISTANCE = 2**(STEPS - 1) + 1
MIN_POSITION = Gitlab::Database::MIN_INT_VALUE
START_POSITION = 0
MAX_POSITION = Gitlab::Database::MAX_INT_VALUE
MAX_GAP = IDEAL_DISTANCE * 2
MIN_GAP = 2
NoSpaceLeft = Class.new(StandardError)
include ::Gitlab::RelativePositioning
class_methods do
def move_nulls_to_end(objects)
......@@ -504,8 +80,7 @@ module RelativePositioning
return 0 if objects.empty?
number_of_gaps = objects.size # 1 to the nearest neighbour, and one between each
mover = Mover.new(START_POSITION, (MIN_POSITION..MAX_POSITION))
representative = mover.context(objects.first)
representative = RelativePositioning.mover.context(objects.first)
position = if at_end
representative.max_relative_position
......@@ -562,7 +137,7 @@ module RelativePositioning
end
def self.mover
Mover.new(START_POSITION, (MIN_POSITION..MAX_POSITION))
::Gitlab::RelativePositioning::Mover.new(START_POSITION, (MIN_POSITION..MAX_POSITION))
end
def move_between(before, after)
......
lib/gitlab/relative_positioning.rb 0 → 100644
View file @ ccec75e5
# frozen_string_literal: true
module Gitlab
module RelativePositioning
STEPS = 10
IDEAL_DISTANCE = 2**(STEPS - 1) + 1
MIN_POSITION = Gitlab::Database::MIN_INT_VALUE
START_POSITION = 0
MAX_POSITION = Gitlab::Database::MAX_INT_VALUE
MAX_GAP = IDEAL_DISTANCE * 2
MIN_GAP = 2
NoSpaceLeft = Class.new(StandardError)
end
end
lib/gitlab/relative_positioning/gap.rb 0 → 100644
View file @ ccec75e5
# frozen_string_literal: true
#
module Gitlab
module RelativePositioning
class Gap
attr_reader :start_pos, :end_pos
def initialize(start_pos, end_pos)
@start_pos, @end_pos = start_pos, end_pos
end
def ==(other)
other.is_a?(self.class) && other.start_pos == start_pos && other.end_pos == end_pos
end
def delta
((start_pos - end_pos) / 2.0).abs.ceil.clamp(0, RelativePositioning::IDEAL_DISTANCE)
end
end
end
end
lib/gitlab/relative_positioning/item_context.rb 0 → 100644
View file @ ccec75e5
# frozen_string_literal: true
module Gitlab
module RelativePositioning
# This class is API private - it should not be explicitly instantiated
# outside of tests
# rubocop: disable CodeReuse/ActiveRecord
class ItemContext
include Gitlab::Utils::StrongMemoize
attr_reader :object, :model_class, :range
attr_accessor :ignoring
def initialize(object, range)
@object = object
@range = range
@model_class = object.class
end
def min_relative_position
strong_memoize(:min_relative_position) { calculate_relative_position('MIN') }
end
def max_relative_position
strong_memoize(:max_relative_position) { calculate_relative_position('MAX') }
end
def prev_relative_position
calculate_relative_position('MAX') { |r| nextify(r, false) } if object.relative_position
end
def next_relative_position
calculate_relative_position('MIN') { |r| nextify(r) } if object.relative_position
end
def nextify(relation, gt = true)
if gt
relation.where("relative_position > ?", relative_position)
else
relation.where("relative_position < ?", relative_position)
end
end
def relative_siblings(relation = scoped_items)
object.exclude_self(relation)
end
# Handles the possibility that the position is already occupied by a sibling
def place_at_position(position, lhs)
current_occupant = relative_siblings.find_by(relative_position: position)
if current_occupant.present?
Mover.new(position, range).move(object, lhs.object, current_occupant)
else
object.relative_position = position
end
end
def lhs_neighbour
scoped_items
.where('relative_position < ?', relative_position)
.reorder(relative_position: :desc)
.first
.then { |x| neighbour(x) }
end
def rhs_neighbour
scoped_items
.where('relative_position > ?', relative_position)
.reorder(relative_position: :asc)
.first
.then { |x| neighbour(x) }
end
def neighbour(item)
return unless item.present?
n = self.class.new(item, range)
n.ignoring = ignoring
n
end
def scoped_items
r = model_class.relative_positioning_query_base(object)
r = object.exclude_self(r, excluded: ignoring) if ignoring.present?
r
end
def calculate_relative_position(calculation)
# When calculating across projects, this is much more efficient than
# MAX(relative_position) without the GROUP BY, due to index usage:
# https://gitlab.com/gitlab-org/gitlab-foss/issues/54276#note_119340977
relation = scoped_items
.order(Gitlab::Database.nulls_last_order('position', 'DESC'))
.group(grouping_column)
.limit(1)
relation = yield relation if block_given?
relation
.pluck(grouping_column, Arel.sql("#{calculation}(relative_position) AS position"))
.first&.last
end
def grouping_column
model_class.relative_positioning_parent_column
end
def max_sibling
sib = relative_siblings
.order(Gitlab::Database.nulls_last_order('relative_position', 'DESC'))
.first
self.class.new(sib, range)
end
def min_sibling
sib = relative_siblings
.order(Gitlab::Database.nulls_last_order('relative_position', 'ASC'))
.first
self.class.new(sib, range)
end
def shift_left
move_sequence_before(true)
object.reset
end
def shift_right
move_sequence_after(true)
object.reset
end
def create_space_left
find_next_gap_before.tap { |gap| move_sequence_before(false, next_gap: gap) }
end
def create_space_right
find_next_gap_after.tap { |gap| move_sequence_after(false, next_gap: gap) }
end
# Moves the sequence before the current item to the middle of the next gap
# For example, we have
#
# 5 . . . . . 11 12 13 14 [15] 16 . 17
# -----------
#
# This moves the sequence [11 12 13 14] to [8 9 10 11], so we have:
#
# 5 . . 8 9 10 11 . . . [15] 16 . 17
# ---------
#
# Creating a gap to the left of the current item. We can understand this as
# dividing the 5 spaces between 5 and 11 into two smaller gaps of 2 and 3.
#
# If `include_self` is true, the current item will also be moved, creating a
# gap to the right of the current item:
#
# 5 . . 8 9 10 11 [14] . . . 16 . 17
# --------------
#
# As an optimization, the gap can be precalculated and passed to this method.
#
# @api private
# @raises NoSpaceLeft if the sequence cannot be moved
def move_sequence_before(include_self = false, next_gap: find_next_gap_before)
raise NoSpaceLeft unless next_gap.present?
delta = next_gap.delta
move_sequence(next_gap.start_pos, relative_position, -delta, include_self)
end
# Moves the sequence after the current item to the middle of the next gap
# For example, we have:
#
# 8 . 10 [11] 12 13 14 15 . . . . . 21
# -----------
#
# This moves the sequence [12 13 14 15] to [15 16 17 18], so we have:
#
# 8 . 10 [11] . . . 15 16 17 18 . . 21
# -----------
#
# Creating a gap to the right of the current item. We can understand this as
# dividing the 5 spaces between 15 and 21 into two smaller gaps of 3 and 2.
#
# If `include_self` is true, the current item will also be moved, creating a
# gap to the left of the current item:
#
# 8 . 10 . . . [14] 15 16 17 18 . . 21
# ----------------
#
# As an optimization, the gap can be precalculated and passed to this method.
#
# @api private
# @raises NoSpaceLeft if the sequence cannot be moved
def move_sequence_after(include_self = false, next_gap: find_next_gap_after)
raise NoSpaceLeft unless next_gap.present?
delta = next_gap.delta
move_sequence(relative_position, next_gap.start_pos, delta, include_self)
end
def move_sequence(start_pos, end_pos, delta, include_self = false)
relation = include_self ? scoped_items : relative_siblings
object.update_relative_siblings(relation, (start_pos..end_pos), delta)
end
def find_next_gap_before
items_with_next_pos = scoped_items
.select('relative_position AS pos, LEAD(relative_position) OVER (ORDER BY relative_position DESC) AS next_pos')
.where('relative_position <= ?', relative_position)
.order(relative_position: :desc)
find_next_gap(items_with_next_pos, range.first)
end
def find_next_gap_after
items_with_next_pos = scoped_items
.select('relative_position AS pos, LEAD(relative_position) OVER (ORDER BY relative_position ASC) AS next_pos')
.where('relative_position >= ?', relative_position)
.order(:relative_position)
find_next_gap(items_with_next_pos, range.last)
end
def find_next_gap(items_with_next_pos, default_end)
gap = model_class
.from(items_with_next_pos, :items)
.where('next_pos IS NULL OR ABS(pos::bigint - next_pos::bigint) >= ?', MIN_GAP)
.limit(1)
.pluck(:pos, :next_pos)
.first
return if gap.nil? || gap.first == default_end
Gap.new(gap.first, gap.second || default_end)
end
def relative_position
object.relative_position
end
end
# rubocop: enable CodeReuse/ActiveRecord
end
end
lib/gitlab/relative_positioning/mover.rb 0 → 100644
View file @ ccec75e5
# frozen_string_literal: true
module Gitlab
module RelativePositioning
class Mover
attr_reader :range, :start_position
def initialize(start, range)
@range = range
@start_position = start
end
def move_to_end(object)
focus = context(object, ignoring: object)
max_pos = focus.max_relative_position
move_to_range_end(focus, max_pos)
end
def move_to_start(object)
focus = context(object, ignoring: object)
min_pos = focus.min_relative_position
move_to_range_start(focus, min_pos)
end
def move(object, first, last)
raise ArgumentError unless object && (first || last) && (first != last)
# Moving a object next to itself is a no-op
return if object == first || object == last
lhs = context(first, ignoring: object)
rhs = context(last, ignoring: object)
focus = context(object)
lhs ||= rhs.lhs_neighbour
rhs ||= lhs.rhs_neighbour
if lhs.nil?
move_to_range_start(focus, rhs.relative_position)
elsif rhs.nil?
move_to_range_end(focus, lhs.relative_position)
else
pos_left, pos_right = create_space_between(lhs, rhs)
desired_position = position_between(pos_left, pos_right)
focus.place_at_position(desired_position, lhs)
end
end
def context(object, ignoring: nil)
return unless object
c = ItemContext.new(object, range)
c.ignoring = ignoring
c
end
private
def gap_too_small?(pos_a, pos_b)
return false unless pos_a && pos_b
(pos_a - pos_b).abs < MIN_GAP
end
def move_to_range_end(context, max_pos)
range_end = range.last + 1
new_pos = if max_pos.nil?
start_position
elsif gap_too_small?(max_pos, range_end)
max = context.max_sibling
max.ignoring = context.object
max.shift_left
position_between(max.relative_position, range_end)
else
position_between(max_pos, range_end)
end
context.object.relative_position = new_pos
end
def move_to_range_start(context, min_pos)
range_end = range.first - 1
new_pos = if min_pos.nil?
start_position
elsif gap_too_small?(min_pos, range_end)
sib = context.min_sibling
sib.ignoring = context.object
sib.shift_right
position_between(sib.relative_position, range_end)
else
position_between(min_pos, range_end)
end
context.object.relative_position = new_pos
end
def create_space_between(lhs, rhs)
pos_left = lhs&.relative_position
pos_right = rhs&.relative_position
return [pos_left, pos_right] unless gap_too_small?(pos_left, pos_right)
gap = rhs.create_space_left
[pos_left - gap.delta, pos_right]
rescue NoSpaceLeft
gap = lhs.create_space_right
[pos_left, pos_right + gap.delta]
end
# This method takes two integer values (positions) and
# calculates the position between them. The range is huge as
# the maximum integer value is 2147483647.
#
# We avoid open ranges by clamping the range to [MIN_POSITION, MAX_POSITION].
#
# Then we handle one of three cases:
# - If the gap is too small, we raise NoSpaceLeft
# - If the gap is larger than MAX_GAP, we place the new position at most
# IDEAL_DISTANCE from the edge of the gap.
# - otherwise we place the new position at the midpoint.
#
# The new position will always satisfy: pos_before <= midpoint <= pos_after
#
# As a precondition, the gap between pos_before and pos_after MUST be >= 2.
# If the gap is too small, NoSpaceLeft is raised.
#
# @raises NoSpaceLeft
def position_between(pos_before, pos_after)
pos_before ||= range.first
pos_after ||= range.last
pos_before, pos_after = [pos_before, pos_after].sort
gap_width = pos_after - pos_before
if gap_too_small?(pos_before, pos_after)
raise NoSpaceLeft
elsif gap_width > MAX_GAP
if pos_before <= range.first
pos_after - IDEAL_DISTANCE
elsif pos_after >= range.last
pos_before + IDEAL_DISTANCE
else
midpoint(pos_before, pos_after)
end
else
midpoint(pos_before, pos_after)
end
end
def midpoint(lower_bound, upper_bound)
((lower_bound + upper_bound) / 2.0).ceil.clamp(lower_bound, upper_bound - 1)
end
end
end
end
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