to_dot

# File lib/rubygems/resolver/molinillo/lib/molinillo/dependency_graph.rb, line 103
    def to_dot(options = {})
      edge_label = options.delete(:edge_label)
      raise ArgumentError, "Unknown options: #{options.keys}" unless options.empty?

      dot_vertices = []
      dot_edges = []
      vertices.each do |n, v|
        dot_vertices << "  #{n} [label=\"{#{n}|#{v.payload}}\"]"
        v.outgoing_edges.each do |e|
          label = edge_label ? edge_label.call(e) : e.requirement
          dot_edges << "  #{e.origin.name} -> #{e.destination.name} [label=#{label.to_s.dump}]"
        end
      end

      dot_vertices.uniq!
      dot_vertices.sort!
      dot_edges.uniq!
      dot_edges.sort!

      dot = dot_vertices.unshift('digraph G {').push('') + dot_edges.push('}')
      dot.join("\n")
    end