require 'tempfile'

module UniverseCompiler
  module Utils

    module Graphviz

      def graph_entities_to_file(entities,
                                 output_file_name: nil,
                                 file_type: :svg,
                                 generate_file: true,
                                 &block)
        g = GraphViz.new( :G, :type => :digraph )

        cache = {by_node: {}, by_entity: {}}
        # Building nodes 
        entities.each do |entity|
          node = g.add_node entity.as_path
          if entity.respond_to? :graphviz_label
            node[:label] = entity.graphviz_label
          end
          cache[:by_entity][entity] = node
          cache[:by_node][node] = entity
        end
        
        # Building relations
        entities.each do |entity|
          entity.class.fields_constraints.each do |field_name, field_constraints|
            field_constraints.each do |constraint_name, _|
              case constraint_name
              when :has_one
                target = entity[field_name]
                g.add_edges cache[:by_entity][entity], cache[:by_entity][target] unless target.nil?
              when :has_many
                entity[field_name].each do |target|
                  g.add_edges cache[:by_entity][entity], cache[:by_entity][target]
                end
              end
            end
          end
        end

        if block_given?
          case block.arity
          when 1
            yield g
          when 2
            yield g, cache
          else
            raise UniverseCompiler::Error, 'Wrong arity when calling UniverseCompiler::Utils::Graphviz#graph_entities_to_file'
          end
        end

        file_ext = file_type.to_s
        file_ext = (file_ext.start_with? '.') ? file_ext : ".#{file_ext}"

        output_file_name = case output_file_name
                      when NilClass
                        file = Tempfile.create ['entities_graph', file_ext]
                        file.close
                        file.path
                      when String
                        if output_file_name.end_with? file_ext
                          output_file_name
                        else
                          "#{output_file_name}#{file_ext}"
                        end
                      end

        if generate_file
          g.output( file_type => output_file_name )
          UniverseCompiler.logger.debug "Graph file: '#{output_file_name}'"
          output_file_name
        else
          g
        end
      end


    end

  end
end