class TreePrinter
  attr_accessor :is_branch
  attr_accessor :get_children

  def initialize
    @arms = Hash.new("|   ")
    @arms[""]  = ""
    @arms["`"] = "    "
    @out = ""
    @is_branch    = proc{|node| FileTest.directory?(node) && FileTest.readable?(node) }
    @get_children = proc{|node| node.children(false).sort}
    @format_node  = proc{|node| node.to_s}
  end

  def visit(path, leader, tie, arm, node)
    # todo, doesn't quite work for files just yet
    node_str = @format_node.call(node)
    @out << "#{leader}#{arm}#{tie}#{node_str}\n"
    visitChildren(node, leader + @arms[arm])
    @out
  end

  def visitChildren(path, leader)
    return unless @is_branch.call(path)
    kids = @get_children.call(path)
    return if kids.empty?
    arms = Array.new(kids.length - 1, "|") << "`"
    pairs = kids.zip(arms)
    pairs.each { |e|  visit(path, leader, "-- ", e[1], e[0]) }
  end

  def format(root)
    visit root, "", "", "", root
  end
end