Adjusted the Windows LongPath support check for valid segment lengths

Closes #1512

(cherry picked from commit 52c6bc5549ab998ccc018d138c55f8f924eed6d3)

src/NzbDrone.Common/Disk/LongPathSupport.cs

@@ -1,15 +1,79 @@
 using System;
+using System.IO;
+using NzbDrone.Common.EnvironmentInfo;
 
 namespace NzbDrone.Common.Disk
 {
     public static class LongPathSupport
     {
+        private static int MAX_PATH;
+        private static int MAX_NAME;
+
         public static void Enable()
         {
             // Mono has an issue with enabling long path support via app.config.
             // This works for both mono and .net on Windows.
             AppContext.SetSwitch("Switch.System.IO.UseLegacyPathHandling", false);
             AppContext.SetSwitch("Switch.System.IO.BlockLongPaths", false);
+
+            DetectLongPathLimits();
+        }
+
+        private static void DetectLongPathLimits()
+        {
+            if (!int.TryParse(Environment.GetEnvironmentVariable("MAX_PATH"), out MAX_PATH))
+            {
+                if (OsInfo.IsLinux)
+                {
+                    MAX_PATH = 4096;
+                }
+                else
+                {
+                    try
+                    {
+                        // Windows paths can be up to 32,767 characters long, but each component of the path must be less than 255.
+                        // If the OS does not have Long Path enabled, then the following will throw an exception
+                        // ref: https://docs.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation
+                        Path.GetDirectoryName($@"C:\{new string('a', 254)}\{new string('a', 254)}");
+                        MAX_PATH = 4096;
+                    }
+                    catch
+                    {
+                        MAX_PATH = 260 - 1;
+                    }
+                }
+            }
+
+            if (!int.TryParse(Environment.GetEnvironmentVariable("MAX_NAME"), out MAX_NAME))
+            {
+                MAX_NAME = 255;
+            }
+        }
+
+        public static int MaxFilePathLength
+        {
+            get
+            {
+                if (MAX_PATH == 0)
+                {
+                    DetectLongPathLimits();
+                }
+
+                return MAX_PATH;
+            }
+        }
+
+        public static int MaxFileNameLength
+        {
+            get
+            {
+                if (MAX_NAME == 0)
+                {
+                    DetectLongPathLimits();
+                }
+
+                return MAX_NAME;
+            }
         }
     }
 }