Move array splitting and rotating to utils

app/services/group_stage_service.rb

@@ -143,10 +143,9 @@ class GroupStageService
       teams_per_group_ranked_transposed = teams_per_group_ranked.transpose
       first_places = teams_per_group_ranked_transposed[0]
       second_places = teams_per_group_ranked_transposed[1]
-      # split the second places in half and place the second half at the beginning
-      # e.g. [1, 2, 3, 4, 5, 6] to [4, 5, 6, 1, 2, 3]
-      mid = second_places.length / 2
-      second_places_new_order = second_places[mid..-1] + second_places[0..mid]
+
+      second_places_new_order = split_and_rotate(second_places)
+
       # zip the first and second places together
       # e.g. [1, 2, 3], [a, b, c] to [1, a, 2, b, 3, c]
       first_places.zip(second_places_new_order).flatten

app/services/utils.rb

@@ -29,4 +29,17 @@ class Utils
   def self.po2?(number)
     number.to_s(2).count('1') == 1
   end
+
+  # split the array in half and place the second half at the beginning
+  # e.g. [1, 2, 3, 4, 5, 6] to [4, 5, 6, 1, 2, 3]
+  def split_and_rotate(array)
+    # handle the case where the array has an odd number of elements
+    middle_element = []
+    if array.length.odd?
+      # pop the last element and place it in the middle
+      middle_element = [array.pop]
+    end
+    mid = array.length / 2
+    array[mid..-1] + middle_element + array[0..mid]
+  end
 end

spec/services/utils_spec.rb

@@ -47,4 +47,20 @@ RSpec.describe Utils do
       expect(Utils.po2?(parameters[:test])).to eq(parameters[:result])
     end
   end
+
+  describe '#split_and_rotate' do
+    [
+      { test: [1, 2, 3, 4, 5, 6], result: [4, 5, 6, 1, 2, 3] },
+      { test: [1, 2, 3, 4, 5], result: [3, 4, 5, 1, 2] },
+      { test: [1, 2, 3, 4], result: [3, 4, 1, 2] },
+      { test: [1, 2, 3], result: [2, 3, 1] },
+      { test: [1, 2], result: [2, 1] },
+      { test: [1], result: [1] },
+      { test: [], result: [] }
+    ].each do |parameters|
+      it "splits and rotates #{parameters[:test]} to #{parameters[:result]}" do
+        expect(Utils.new.split_and_rotate(parameters[:test])).to eq(parameters[:result])
+      end
+    end
+  end
 end