Add the cyclic plane (circular array) implementation w/testing

2 files changed, 66 insertions, 0 deletions

diff --git a/CLI/ruby/lib/game_of_life/plane.rb b/CLI/ruby/lib/game_of_life/plane.rb
new file mode 100644
index 0000000..f866754
--- /dev/null
+++ b/CLI/ruby/lib/game_of_life/plane.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module GameOfLife
+  # Custom Plane class that represent a cyclic/circular plane/array
+  # This class would always return an element unless the array is empty
+  class Plane < Array
+    # Extending the default array behaviour by treating the array as cyclic/circular object
+    #
+    # @example working with normal array
+    #   a = [0, 1, 2, 3]
+    #   a[-6] == a[-2] == a[2]
+    #   a[-5] == a[-1] == a[3]
+    #   a[-4] == a[0]  == a[4]
+    #   a[-3] == a[1]  == a[5]
+    #   a[-2] == a[2]  == a[6]
+    #   a[-1] == a[3]  == a[7]
+    #   a[0]  == a[4]  == a[8]
+    #
+    # @example working with empty array
+    #   b = []
+    #   b[0] == b[1] == b[-1] == nil
+    def [](index)
+      return nil if empty?
+      super(index % size)
+    end
+  end
+end
diff --git a/CLI/ruby/spec/plane_spec.rb b/CLI/ruby/spec/plane_spec.rb
new file mode 100644
index 0000000..c4efbb4
--- /dev/null
+++ b/CLI/ruby/spec/plane_spec.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+RSpec.describe GameOfLife::Plane do
+  describe "#[]" do
+    context "when empty" do
+      subject { described_class.new }
+
+      it "returns nil with [-1]" do
+        expect(subject[-1]).to be_nil
+      end
+
+      it "returns nil with [0]" do
+        expect(subject[0]).to be_nil
+      end
+
+      it "returns nil with [1]" do
+        expect(subject[1]).to be_nil
+      end
+    end
+
+    context "when not empty" do
+      subject { described_class.new([0, 1, 2, 3]) }
+
+      it "returns value at index" do
+        expect(subject[0]).to eq 0
+      end
+
+      it "returns value at -index (negative indices count backward from the end of the array)" do
+        expect(subject[-5]).to eq 3
+        expect(subject[-1]).to eq 3
+      end
+
+      it "returns value at any index (indices bigger than size cycle again from the beginning)" do
+        expect(subject[5]).to eq 1
+        expect(subject[9]).to eq 1
+      end
+    end
+  end
+end