Allow issues in boards to be ordered

1 files changed, 132 insertions, 0 deletions

diff --git a/app/models/concerns/relative_positioning.rb b/app/models/concerns/relative_positioning.rb
new file mode 100644
index 00000000000..b9af6350c07
--- /dev/null
+++ b/app/models/concerns/relative_positioning.rb
@@ -0,0 +1,132 @@
+module RelativePositioning
+  extend ActiveSupport::Concern
+
+  MIN_POSITION = Float::MIN
+  MAX_POSITION = Float::MAX
+
+  included do
+    after_save :save_positionable_neighbours
+  end
+
+  def min_relative_position
+    self.class.minimum(:relative_position)
+  end
+
+  def max_relative_position
+    self.class.maximum(:relative_position)
+  end
+
+  def prev_relative_position
+    prev_pos = nil
+
+    if self.relative_position
+      prev_pos = self.class.
+        where('relative_position < ?', self.relative_position).
+        maximum(:relative_position)
+    end
+
+    prev_pos || MIN_POSITION
+  end
+
+  def next_relative_position
+    next_pos = nil
+
+    if self.relative_position
+      next_pos = self.class.
+        where('relative_position > ?', self.relative_position).
+        minimum(:relative_position)
+    end
+
+    next_pos || MAX_POSITION
+  end
+
+  def move_between(before, after)
+    return move_nowhere unless before || after
+    return move_after(before) if before && !after
+    return move_before(after) if after && !before
+
+    pos_before = before.relative_position
+    pos_after = after.relative_position
+
+    if pos_before && pos_after
+      if pos_before == pos_after
+        pos = pos_before
+
+        self.relative_position = pos
+        before.move_before(self)
+        after.move_after(self)
+        @positionable_neighbours = [before, after]
+      else
+        self.relative_position = position_between(pos_before, pos_after)
+      end
+    elsif pos_before
+      self.move_after(before)
+      after.move_after(self)
+      @positionable_neighbours = [after]
+    elsif pos_after
+      self.move_before(after)
+      before.move_before(self)
+      @positionable_neighbours = [before]
+    else
+      move_to_end
+      before.move_before(self)
+      after.move_after(self)
+      @positionable_neighbours = [before, after]
+    end
+  end
+
+  def move_before(after)
+    pos_after = after.relative_position
+    if pos_after
+      self.relative_position = position_between(after.prev_relative_position, pos_after)
+    else
+      move_to_end
+      after.move_after(self)
+      @positionable_neighbours = [after]
+    end
+  end
+
+  def move_after(before)
+    pos_before = before.relative_position
+    if pos_before
+      self.relative_position = position_between(pos_before, before.next_relative_position)
+    else
+      move_to_end
+      before.move_before(self)
+      @positionable_neighbours = [before]
+    end
+  end
+
+  def move_nowhere
+    self.relative_position = nil
+  end
+
+  def move_to_front
+    self.relative_position = position_between(MIN_POSITION, min_relative_position || MAX_POSITION)
+  end
+
+  def move_to_end
+    self.relative_position = position_between(max_relative_position || MIN_POSITION, MAX_POSITION)
+  end
+
+  def move_between!(*args)
+    move_between(*args) && save!
+  end
+
+  private
+
+  def position_between(pos_before, pos_after)
+    pos_before, pos_after = [pos_before, pos_after].sort
+
+    pos_before + (pos_after - pos_before) / 2
+  end
+
+  def save_positionable_neighbours
+    return unless @positionable_neighbours
+
+    @positionable_neighbours.each(&:save)
+    @positionable_neighbours = nil
+
+    true
+  end
+end