class RBS::Prototype::NodeUsage

def calculate(node, conditional:)
  if conditional
    conditional_nodes << node
  end
  case node.type
  when :IF, :UNLESS
    cond_node, true_node, false_node = node.children
    calculate(cond_node, conditional: true)
    calculate(true_node, conditional: conditional) if true_node
    calculate(false_node, conditional: conditional) if false_node
  when :AND, :OR
    left, right = node.children
    calculate(left, conditional: true)
    calculate(right, conditional: conditional)
  when :QCALL
    receiver, _, args = node.children
    calculate(receiver, conditional: true)
    calculate(args, conditional: false) if args
  when :WHILE
    cond, body = node.children
    calculate(cond, conditional: true)
    calculate(body, conditional: false) if body
  when :OP_ASGN_OR, :OP_ASGN_AND
    var, _, asgn = node.children
    calculate(var, conditional: true)
    calculate(asgn, conditional: conditional)
  when :LASGN, :IASGN, :GASGN
    _, lhs = node.children
    calculate(lhs, conditional: conditional) if lhs
  when :MASGN
    lhs, _ = node.children
    calculate(lhs, conditional: conditional)
  when :CDECL
    if node.children.size == 2
      _, lhs = node.children
      calculate(lhs, conditional: conditional)
    else
      const, _, lhs = node.children
      calculate(const, conditional: false)
      calculate(lhs, conditional: conditional)
    end
  when :SCOPE
    _, _, body = node.children
    calculate(body, conditional: conditional)
  when :CASE2
    _, *branches = node.children
    branches.each do |branch|
      if branch.type == :WHEN
        list, body = branch.children
        list.children.each do |child|
          if child
            calculate(child, conditional: true)
          end
        end
        calculate(body, conditional: conditional)
      else
        calculate(branch, conditional: conditional)
      end
    end
  when :BLOCK
    *nodes, last = node.children
    nodes.each do |no|
      calculate(no, conditional: false)
    end
    calculate(last, conditional: conditional) if last
  else
    each_child(node) do |child|
      calculate(child, conditional: false)
    end
  end
end

def each_conditional_node(&block)
  if block
    conditional_nodes.each(&block)
  else
    conditional_nodes.each
  end
end

def initialize(node)
  @node = node
  @conditional_nodes = Set[].compare_by_identity
  calculate(node, conditional: false)
end