Implement Utils.sort_tuples! for user-defined sorting

lib/utils.rb

@@ -79,4 +79,44 @@ module Utils
   def self.pretty_jsonify(thing)
     JSON.pretty_generate(thing).gsub('</', '<\/')
   end
+
+  class TupleSorter
+    class SortableTuple
+      attr_reader :array
+
+      # The <=> method will call orders[n] to determine if the nth element
+      # should be compared in descending order.
+      def initialize(array, orders = [])
+        @array = array
+        @orders = orders
+      end
+
+      def <=> other
+        other = other.array
+        @array.each_with_index do |e, i|
+          case cmp = e <=> other[i]
+          when nil
+            return nil
+          when 0
+            next
+          else
+            return @orders[i] ? -cmp : cmp
+          end
+        end
+        0
+      end
+    end
+
+    class << self
+      def sort!(array, orders = [])
+        array.sort_by! do |e|
+          SortableTuple.new(e, orders)
+        end
+      end
+    end
+  end
+
+  def self.sort_tuples!(array, orders = [])
+    TupleSorter.sort!(array, orders)
+  end
 end

spec/lib/utils_spec.rb

@@ -114,4 +114,44 @@ describe Utils do
       expect(cleaned_json).to include("<\\/script>")
     end
   end
+
+  describe "#sort_tuples!" do
+    let(:tuples) {
+      time = Time.now
+      [
+        [2, "a", time - 1],  # 0
+        [2, "b", time - 1],  # 1
+        [1, "b", time - 1],  # 2
+        [1, "b", time],      # 3
+        [1, "a", time],      # 4
+        [2, "a", time + 1],  # 5
+        [2, "a", time],      # 6
+      ]
+    }
+
+    it "sorts tuples like arrays by default" do
+      expected = tuples.values_at(4, 2, 3, 0, 6, 5, 1)
+
+      Utils.sort_tuples!(tuples)
+      expect(tuples).to eq expected
+    end
+
+    it "sorts tuples in order specified: case 1" do
+      # order by x1 asc, x2 desc, c3 asc
+      orders = [false, true, false]
+      expected = tuples.values_at(2, 3, 4, 1, 0, 6, 5)
+
+      Utils.sort_tuples!(tuples, orders)
+      expect(tuples).to eq expected
+    end
+
+    it "sorts tuples in order specified: case 2" do
+      # order by x1 desc, x2 asc, c3 desc
+      orders = [true, false, true]
+      expected = tuples.values_at(5, 6, 0, 1, 4, 3, 2)
+
+      Utils.sort_tuples!(tuples, orders)
+      expect(tuples).to eq expected
+    end
+  end
 end