Implement shift perturbation

app/jobs/table_simulator_job.rb

@@ -7,6 +7,7 @@ class TableSimulatorJob < ApplicationJob
     engine = VNS::Engine.new
 
     engine.add_perturbation(Tables::Swap)
+    engine.add_perturbation(Tables::Shift)
 
     initial_solution = Tables::Distribution.new(min_per_table: 8, max_per_table: 10)
     initial_solution.random_distribution(Guest.potential.shuffle)

app/services/tables/shift.rb

@@ -0,0 +1,30 @@
+# Copyright (C) 2024 Manuel Bustillo
+
+module Tables
+  class Shift
+    private attr_reader :initial_solution
+    def initialize(initial_solution)
+      @initial_solution = initial_solution
+    end
+
+    def each
+      @initial_solution.tables.permutation(2) do |table_a, table_b|
+        table_a.dup.each do |person|
+          original_discomfort_a = table_a.reset
+          original_discomfort_b = table_b.reset
+
+          table_a.delete(person)
+          table_b << person
+
+          yield(@initial_solution)
+        ensure
+          table_b.delete(person)
+          table_a << person
+
+          table_a.discomfort = original_discomfort_a
+          table_b.discomfort = original_discomfort_b
+        end
+      end
+    end
+  end
+end

spec/services/tables/shift_spec.rb

@@ -0,0 +1,53 @@
+require 'rails_helper'
+
+module Tables
+  RSpec.describe Shift do
+    describe '#each' do
+      let(:shifts) do
+        acc = []
+        described_class.new(initial_solution).each do |solution|
+          acc << solution.tables.map(&:dup)
+        end
+        acc
+      end
+
+      context 'when there are two tables with two people each' do
+        let(:initial_solution) do
+          Distribution.new(min_per_table: 2, max_per_table: 2).tap do |distribution|
+            distribution.tables << Set[:a, :b].to_table
+            distribution.tables << Set[:c, :d].to_table
+          end
+        end
+
+        it 'yields all possible shifts between the tables' do
+          expect(shifts).to contain_exactly(
+            [Set[:b], Set[:c, :d, :a]],
+            [Set[:a], Set[:c, :d, :b]],
+            [Set[:b, :a, :d], Set[:c]],
+            [Set[:b, :a, :c], Set[:d]]
+          )
+        end
+      end
+
+      context 'when there are two tables with three people each' do
+        let(:initial_solution) do
+          Distribution.new(min_per_table: 3, max_per_table: 3).tap do |distribution|
+            distribution.tables << Set[:a, :b, :c].to_table
+            distribution.tables << Set[:d, :e, :f].to_table
+          end
+        end
+
+        it 'yields all possible shifts between the tables' do
+          expect(shifts).to contain_exactly(
+            [Set[:b, :c], Set[:d, :e, :f, :a]],
+            [Set[:c, :a], Set[:d, :e, :f, :b]],
+            [Set[:a, :b], Set[:d, :e, :f, :c]],
+            [Set[:a, :b, :c, :d], Set[:e, :f]],
+            [Set[:a, :b, :c, :e], Set[:d, :f]],
+            [Set[:a, :b, :c, :f], Set[:d, :e]]
+          )
+        end
+      end
+    end
+  end
+end