ERDBuilder using mother flipping ruby-graphviz

erd_builder.rb

require 'rubygems'
require 'graphviz'

class ERDBuilder

  attr_reader :name

  def add_entity(name)
    ERDEntity.new.tap do |entity|
      entity.build(graph: graph, name: name)
    end
  end

  def associate(entity, other_entity, attributes)
    diagram.add_edges(entity.name, other_entity.name, edge_attributes_for(attributes))
  end

  def begin_system(name)
    @name = name

    # Initialize these objects
    diagram
    graph
  end

  def export_as_png
    diagram.output(png: "#{name}.png")
  end

private

  def diagram
    @diagram ||= GraphViz.digraph(name) do |graph_models_diagram|
      graph_models_diagram[:overlap] = 'false'
      graph_models_diagram[:splines] = 'true'
    end
  end

  def edge_attributes_for(attributes)
    case attributes[:association]
    when :many_to_one
      arrowhead = 'crow'
      arrowtail = 'odot'
    else
      arrowhead = 'odot'
      arrowtail = 'odot'
    end

    label = attributes[:name] || "Label"

    {
      arrowhead: arrowhead,
      arrowtail: arrowtail,
      dir: 'both',
      label: label
    }
  end

  def graph
    @graph ||= @diagram.add_graph(name).tap do |graph|
      graph[:overlap] = 'false'
      graph[:rank]    = 'same'
      graph[:splines] = 'true'
    end
  end

end

class ERDEntity

  attr_reader :name

  def attributes=(attributes)
    attributes_as_string = attributes.collect do |key, value|
      "#{key} :#{value}"
    end.join('\l')

    @node.label = "{#{name}| #{attributes_as_string}}"
  end

  def build(attributes)
    @graph = attributes[:graph]
    @name  = attributes[:name]

    @node = @graph.add_nodes(name, shape: 'record')
  end

end