class ActionDispatch::Journey::NFA::Visitor

def initialize(tt)
  @tt = tt
  @i  = -1
end

def terminal(node)
  from_i = @i += 1 # new state
  to_i   = @i += 1 # new state
  @tt[from_i, to_i] = node
  @tt.accepting = to_i
  @tt.add_memo(to_i, node.memo)
  [from_i, to_i]
end

def visit_CAT(node)
  left  = visit(node.left)
  right = visit(node.right)
  @tt.merge(left.last, right.first)
  [left.first, right.last]
end

def visit_GROUP(node)
  from  = @i += 1
  left  = visit(node.left)
  to    = @i += 1
  @tt.accepting = to
  @tt[from, left.first] = nil
  @tt[left.last, to] = nil
  @tt[from, to] = nil
  [from, to]
end

def visit_OR(node)
  from = @i += 1
  children = node.children.map { |c| visit(c) }
  to   = @i += 1
  children.each do |child|
    @tt[from, child.first] = nil
    @tt[child.last, to]    = nil
  end
  @tt.accepting = to
  [from, to]
end