Use immutable data structures to calculate variations

app/services/tables/distribution.rb

@@ -12,6 +12,22 @@ module Tables
       @tables.values.freeze
     end
 
+    def deep_freeze
+      @tables.each_value(&:freeze)
+      @tables.freeze
+      freeze
+    end
+
+    def replace(table)
+      @tables[table.id] = table
+    end
+
+    def dup
+      super.tap do |new_distribution|
+        new_distribution.instance_variable_set(:@tables, @tables.dup)
+      end
+    end
+
     def <<(array)
       Table.new(array).tap do |table|
         @tables[table.id] = table
@@ -22,6 +38,9 @@ module Tables
       @tables = {}
 
       self << people.slice!(0..rand(@min_per_table..@max_per_table)) while people.any?
+
+      @tables.freeze
+      freeze
     end
 
     def discomfort

app/services/tables/swap.rb

@@ -8,25 +8,23 @@ module Tables
     def each
       @initial_solution.tables.combination(2) do |table_a, table_b|
         table_a.product(table_b).each do |(person_a, person_b)|
-          original_discomfort_a = table_a.reset
+          new_solution = @initial_solution.dup
-          original_discomfort_b = table_b.reset
 
-          table_a.delete(person_a)
+          new_table_a = table_a.dup
-          table_b.delete(person_b)
+          new_table_b = table_b.dup
 
-          table_a << person_b
+          new_solution.replace(new_table_a)
-          table_b << person_a
+          new_solution.replace(new_table_b)
 
-          yield(@initial_solution)
+          new_table_a.delete(person_a)
-        ensure
+          new_table_b.delete(person_b)
-          table_a.delete(person_b)
-          table_b.delete(person_a)
 
-          table_a << person_a
+          new_table_a << person_b
-          table_b << person_b
+          new_table_b << person_a
 
-          table_a.discomfort = original_discomfort_a
+          new_solution.freeze
-          table_b.discomfort = original_discomfort_b
+
+          yield(new_solution)
         end
       end
     end

app/services/tables/table.rb

@@ -18,5 +18,11 @@ module Tables
     def discomfort
       @discomfort ||= DiscomfortCalculator.new(self).calculate
     end
+
+    def dup
+      super.tap do |new_table|
+        new_table.discomfort = nil
+      end
+    end
   end
 end

db/seeds.rb

@@ -1,4 +1,4 @@
-NUMBER_OF_GUESTS = 50
+NUMBER_OF_GUESTS = ENV['SEED_GUEST_COUNT'].presence.to_i || 50
 
 TablesArrangement.delete_all
 Expense.delete_all
@@ -21,7 +21,6 @@ Expense.create!(name: 'Transportation', amount: 3000, pricing_type: 'fixed')
 Expense.create!(name: 'Invitations', amount: 200, pricing_type: 'fixed')
 Expense.create!(name: 'Cake', amount: 500, pricing_type: 'fixed')
 
-
 samples = {
   close_family_a: 10,
   close_family_b: 10,