From c745dbca3cc12433fa145dcc57581ff6d7dce712 Mon Sep 17 00:00:00 2001
From: benjaminZale <benjamin.zale@gmail.com>
Date: Sun, 14 Mar 2021 12:43:29 -0400
Subject: [PATCH] Implementation of Npath complexity for the OpenCover reports
 (#1058)

Implementation of Npath complexity for the OpenCover reports
---
 src/coverlet.core/CoverageSummary.cs          | 34 +++++++++++++++++++
 .../Reporters/OpenCoverReporter.cs            |  3 +-
 .../Reporters/OpenCoverReporterTests.cs       |  1 +
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/src/coverlet.core/CoverageSummary.cs b/src/coverlet.core/CoverageSummary.cs
index 5a64e0b..188e204 100644
--- a/src/coverlet.core/CoverageSummary.cs
+++ b/src/coverlet.core/CoverageSummary.cs
@@ -73,6 +73,40 @@ namespace Coverlet.Core
             return details;
         }
 
+        public int CalculateNpathComplexity(IList<BranchInfo> branches)
+        {
+            // Adapted from OpenCover see https://github.com/OpenCover/opencover/blob/master/main/OpenCover.Framework/Persistance/BasePersistance.cs#L419
+            if (!branches.Any())
+            {
+                return 0;
+            }
+
+            var paths = new Dictionary<int, int>();
+            foreach (var branch in branches)
+            {
+                if (!paths.TryGetValue(branch.Offset, out int count))
+                {
+                    count = 0;
+                }
+                paths[branch.Offset] = ++count;
+            }
+
+            int npath = 1;
+            foreach (var branchPoints in paths.Values)
+            {
+                try
+                {
+                    npath = checked(npath * branchPoints);
+                }
+                catch (OverflowException)
+                {
+                    npath = int.MaxValue;
+                    break;
+                }
+            }
+            return npath;
+        }
+
         public int CalculateCyclomaticComplexity(IList<BranchInfo> branches)
         {
             return Math.Max(1, branches.Count);
diff --git a/src/coverlet.core/Reporters/OpenCoverReporter.cs b/src/coverlet.core/Reporters/OpenCoverReporter.cs
index ac31f4d..6d4c7b6 100644
--- a/src/coverlet.core/Reporters/OpenCoverReporter.cs
+++ b/src/coverlet.core/Reporters/OpenCoverReporter.cs
@@ -78,11 +78,12 @@ namespace Coverlet.Core.Reporters
                             var methLineCoverage = summary.CalculateLineCoverage(meth.Value.Lines);
                             var methBranchCoverage = summary.CalculateBranchCoverage(meth.Value.Branches);
                             var methCyclomaticComplexity = summary.CalculateCyclomaticComplexity(meth.Value.Branches);
+                            var methNpathComplexity = summary.CalculateNpathComplexity(meth.Value.Branches);
 
                             XElement method = new XElement("Method");
 
                             method.Add(new XAttribute("cyclomaticComplexity", methCyclomaticComplexity.ToString()));
-                            method.Add(new XAttribute("nPathComplexity", "0"));
+                            method.Add(new XAttribute("nPathComplexity", methCyclomaticComplexity.ToString()));
                             method.Add(new XAttribute("sequenceCoverage", methLineCoverage.Percent.ToString("G", CultureInfo.InvariantCulture)));
                             method.Add(new XAttribute("branchCoverage", methBranchCoverage.Percent.ToString("G", CultureInfo.InvariantCulture)));
                             method.Add(new XAttribute("isConstructor", meth.Key.Contains("ctor").ToString()));
diff --git a/test/coverlet.core.tests/Reporters/OpenCoverReporterTests.cs b/test/coverlet.core.tests/Reporters/OpenCoverReporterTests.cs
index 75698b6..828e4ab 100644
--- a/test/coverlet.core.tests/Reporters/OpenCoverReporterTests.cs
+++ b/test/coverlet.core.tests/Reporters/OpenCoverReporterTests.cs
@@ -27,6 +27,7 @@ namespace Coverlet.Core.Reporters.Tests
             XDocument doc = XDocument.Load(new MemoryStream(Encoding.UTF8.GetBytes(report)));
             Assert.Empty(doc.Descendants().Attributes("sequenceCoverage").Where(v => v.Value != "33.33"));
             Assert.Empty(doc.Descendants().Attributes("branchCoverage").Where(v => v.Value != "25"));
+            Assert.Empty(doc.Descendants().Attributes("nPathComplexity").Where(v => v.Value != "4"));
         }
 
         [Fact]