class StraightSkeleton::Split

def initialize(nodes, point, travel, source, node)
  @original, @nodes, @point, @travel, @source, @normal = self, nodes, point, travel, source, node.normals[1]
end

def replace!(&block)
  dup.split!(0, &block)
  dup.split!(1, &block)
  block.call @source
end

def split!(index, &block)
  @neighbours = [@source.neighbours[index], @edge[1-index]].rotate index
  @neighbours.inject(&:equal?) ? block.call(prev, prev.is_a?(Collapse) ? 1 : 0) : insert! if @neighbours.any?
end

def viable?
  return false unless @source.active?
  @edge = @nodes.track(@normal).find do |edge|
    (n00, n01), (n10, n11) = edge.map(&:normals)
    p0, p1 = edge.map(&:point)
    next if (point - p0).cross(n00 ? n00 + n01 : n01) < 0
    next if (point - p1).cross(n11 ? n11 + n10 : n10) > 0
    true
  end
end