From 7a06753bdeefa31cff93b92fc62f002d76ef32b1 Mon Sep 17 00:00:00 2001
From: Robert Greiner <robert@robertgreiner.com>
Date: Mon, 14 Nov 2011 15:17:24 -0600
Subject: [PATCH] Added functionality to find opposite reviews between two
 users.

---
 .../Common/FindOppositeReviewsTests.cs        | 47 +++++++++++++++++++
 .../Common/FindSimilarReviewsTests.cs         | 10 ++--
 Recommender/Common/FindOppositeReviews.cs     | 39 +++++++++++++++
 3 files changed, 91 insertions(+), 5 deletions(-)
 create mode 100644 Recommender.Tests/Common/FindOppositeReviewsTests.cs
 create mode 100644 Recommender/Common/FindOppositeReviews.cs

diff --git a/Recommender.Tests/Common/FindOppositeReviewsTests.cs b/Recommender.Tests/Common/FindOppositeReviewsTests.cs
new file mode 100644
index 0000000..5ce56bb
--- /dev/null
+++ b/Recommender.Tests/Common/FindOppositeReviewsTests.cs
@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using NUnit.Framework;
+using Recommender.Common;
+using Recommender.Data;
+
+namespace Recommender.Tests.Common
+{
+    [TestFixture]
+    class FindOppositeReviewsTests
+    {
+
+        [Test]
+        public void TwoDistinctReviewersShouldHaveOneOppositeReview()
+        {
+            var r1 = ReviewerBuilder.BuildOneReviewMax();
+            var r2 = ReviewerBuilder.BuildAReviewerThatReviewedSomethingUnique();
+            Assert.AreEqual(1, new FindOppositeReviews(r1.Reviews, r2.Reviews).Calculate().Count);
+        }
+
+        [Test]
+        public void ShouldReturnSecondUsersUniqueReview()
+        {
+            var r1 = ReviewerBuilder.BuildOneReviewMax();
+            var r2 = ReviewerBuilder.BuildAReviewerThatReviewedSomethingUnique();
+            Assert.AreEqual("Chess", new FindOppositeReviews(r1.Reviews, r2.Reviews).Calculate().First());
+        }
+
+        [Test]
+        public void ReviewersThatHaveTheExactSameTasteShouldHaveNoOppositeItems()
+        {
+            var r1 = ReviewerBuilder.BuildReviewer1();
+            var r2 = ReviewerBuilder.BuildReviewer1();
+            Assert.AreEqual(0, new FindOppositeReviews(r1.Reviews, r2.Reviews).Calculate().Count);
+        }
+
+        [Test]
+        public void ReviewsWithAScoreOfZeroShouldBeIgnored()
+        {
+            var r1 = ReviewerBuilder.BuildAReviewerThatReviewedSomethingUnique();
+            var invalidReviewer = ReviewerBuilder.BuildReviewerWithInvalidReviews();
+            Assert.AreEqual(0, new FindOppositeReviews(r1.Reviews, invalidReviewer.Reviews).Calculate().Count);
+        }
+    }
+}
diff --git a/Recommender.Tests/Common/FindSimilarReviewsTests.cs b/Recommender.Tests/Common/FindSimilarReviewsTests.cs
index decd228..9a157ca 100644
--- a/Recommender.Tests/Common/FindSimilarReviewsTests.cs
+++ b/Recommender.Tests/Common/FindSimilarReviewsTests.cs
@@ -35,16 +35,16 @@ public void ReviewersThatHaveTheSameTasteShouldHaveAllSimilarItems()
         public void ReviewsWithAScoreOfZeroShouldBeIgnored()
         {
             var r1 = ReviewerBuilder.BuildReviewer1();
-            var empty = ReviewerBuilder.BuildReviewerWithInvalidReviews();
-            Assert.AreEqual(0, new FindSimilarReviews(r1.Reviews, empty.Reviews).Calculate().Count);
+            var invalidReviewer = ReviewerBuilder.BuildReviewerWithInvalidReviews();
+            Assert.AreEqual(0, new FindSimilarReviews(r1.Reviews, invalidReviewer.Reviews).Calculate().Count);
         }
 
         [Test]
         public void ReviewsWithAScoreOfZeroShouldBeIgnoredSwitchUsers()
         {
-            var r1 = ReviewerBuilder.BuildReviewer1();
-            var empty = ReviewerBuilder.BuildReviewerWithInvalidReviews();
-            Assert.AreEqual(0, new FindSimilarReviews(empty.Reviews, r1.Reviews).Calculate().Count);
+            var r1 = ReviewerBuilder.BuildAReviewerThatReviewedSomethingUnique();
+            var invalidReviewer = ReviewerBuilder.BuildReviewerWithInvalidReviews();
+            Assert.AreEqual(0, new FindSimilarReviews(invalidReviewer.Reviews, r1.Reviews).Calculate().Count);
         }
     }
 }
diff --git a/Recommender/Common/FindOppositeReviews.cs b/Recommender/Common/FindOppositeReviews.cs
new file mode 100644
index 0000000..7fd42f3
--- /dev/null
+++ b/Recommender/Common/FindOppositeReviews.cs
@@ -0,0 +1,39 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Recommender.Common
+{
+    public class FindOppositeReviews
+    {
+        private readonly Dictionary<string, double> FirstUserReviews;
+        private readonly Dictionary<string, double> SecondUserReviews;
+
+        public FindOppositeReviews(Dictionary<string, double> firstUserReviews, Dictionary<string, double> secondUserReviews)
+        {
+            FirstUserReviews = firstUserReviews;
+            SecondUserReviews = secondUserReviews;
+        }
+
+        public List<string> Calculate()
+        {
+            return (from r in SecondUserReviews where ShouldCountReviewAsOpposite(r) select r.Key).ToList();
+        }
+
+        private bool ShouldCountReviewAsOpposite(KeyValuePair<string, double> r)
+        {
+            return IsReviewUnique(r) && IsReviewValid(SecondUserReviews[r.Key]);
+        }
+
+        private static bool IsReviewValid(double value)
+        {
+            return value > 0.0;
+        }
+
+        private bool IsReviewUnique(KeyValuePair<string, double> r)
+        {
+            return !FirstUserReviews.ContainsKey(r.Key);
+        }
+    }
+}