module FixtureBackground
  class Generator
    def initialize(fixture_name, version, background_dir, blocks, test_unit_class)
      @fixture_name, @version, @background_dir, @blocks, @test_unit_class = fixture_name, version, background_dir, blocks, test_unit_class
    end
    
    def generate!
      remove_background_dir
      create_background_dir
      
      transaction_with_rollback do
        
        bm = Benchmark.realtime do
          dump_ivars do |klass|
            @blocks.each do |block|
              klass.instance_eval(&block)
            end
          end
          dump_fixtures
        end
        
        File.open("#{@background_dir}/.version", 'w+') do |f| 
          f.write @version
        end
        
        puts "Instanciating #{@fixture_name} took #{bm}ms"
      end
    rescue Exception
      remove_background_dir
      raise
    end
    
    private
    
      def transaction_with_rollback
        ActiveRecord::Base.connection.increment_open_transactions
        ActiveRecord::Base.connection.begin_db_transaction
        yield
        ActiveRecord::Base.connection.rollback_db_transaction
        ActiveRecord::Base.connection.decrement_open_transactions
      end
      
      def create_background_dir
        FileUtils.mkdir_p(@background_dir)
      end
      
      def remove_background_dir
        FileUtils.rm_rf(@background_dir)
      end
      
      def dump_ivars
        klass = @test_unit_class.new("collect_ivars")
        existing_ivars = klass.instance_variables
        
        yield klass
        
        ivars_with_value = (klass.instance_variables - existing_ivars).inject({}) do |memo, ivar|
          memo[ivar] = klass.instance_variable_get(ivar)
          memo
        end
        
        ivar_hash = IVars.serialize(ivars_with_value)
        
        File.open("#{@background_dir}/ivars.dump", 'w+') do |f|
          YAML.dump(ivar_hash, f)
        end
      end
      
      def dump_fixtures
        (ActiveRecord::Base.connection.tables - ["schema_migrations"]).each do |table_name|
          begin
            klass = table_name.classify.constantize
            
            records = klass.all
            next if records.empty?
            
            fixtures = {}
            records.each do |record|
              fixtures[table_name + record.id.to_s] = record.instance_variable_get(:@attributes)
            end
          
            File.open("#{@background_dir}/#{table_name}.yml", 'w+') do |f|
              YAML.dump(fixtures, f)
            end
          rescue NameError # do not die on tables that have no model
            puts "cannot dump from #{table_name} as no model exists"
          end
        end
      end
  end
end