1 files changed, 56 insertions, 0 deletions
diff --git a/Emby.Server.Implementations/Library/PathExtensions.cs b/Emby.Server.Implementations/Library/PathExtensions.cs
index 06ff3e611..7dcc925c2 100644
--- a/Emby.Server.Implementations/Library/PathExtensions.cs
+++ b/Emby.Server.Implementations/Library/PathExtensions.cs
@@ -1,6 +1,8 @@
 #nullable enable
 
 using System;
+using System.Diagnostics.CodeAnalysis;
+using System.IO;
 using System.Text.RegularExpressions;
 
 namespace Emby.Server.Implementations.Library
@@ -47,5 +49,59 @@ namespace Emby.Server.Implementations.Library
 
             return null;
         }
+
+        /// <summary>
+        /// Replaces a sub path with another sub path and normalizes the final path.
+        /// </summary>
+        /// <param name="path">The original path.</param>
+        /// <param name="subPath">The original sub path.</param>
+        /// <param name="newSubPath">The new sub path.</param>
+        /// <param name="newPath">The result of the sub path replacement</param>
+        /// <returns>The path after replacing the sub path.</returns>
+        /// <exception cref="ArgumentNullException"><paramref name="path" />, <paramref name="newSubPath" /> or <paramref name="newSubPath" /> is empty.</exception>
+        public static bool TryReplaceSubPath(this string path, string subPath, string newSubPath, [NotNullWhen(true)] out string? newPath)
+        {
+            newPath = null;
+
+            if (string.IsNullOrEmpty(path) || string.IsNullOrEmpty(subPath) || string.IsNullOrEmpty(newSubPath) || subPath.Length > path.Length)
+            {
+                return false;
+            }
+
+            char oldDirectorySeparatorChar;
+            char newDirectorySeparatorChar;
+            // True normalization is still not possible https://github.com/dotnet/runtime/issues/2162
+            // The reasoning behind this is that a forward slash likely means it's a Linux path and
+            // so the whole path should be normalized to use / and vice versa for Windows (although Windows doesn't care much).
+            if (newSubPath.Contains('/', StringComparison.Ordinal))
+            {
+                oldDirectorySeparatorChar = '\\';
+                newDirectorySeparatorChar = '/';
+            }
+            else
+            {
+                oldDirectorySeparatorChar = '/';
+                newDirectorySeparatorChar = '\\';
+            }
+
+            path = path.Replace(oldDirectorySeparatorChar, newDirectorySeparatorChar);
+            subPath = subPath.Replace(oldDirectorySeparatorChar, newDirectorySeparatorChar);
+
+            // We have to ensure that the sub path ends with a directory separator otherwise we'll get weird results
+            // when the sub path matches a similar but in-complete subpath
+            var oldSubPathEndsWithSeparator = subPath[^1] == newDirectorySeparatorChar;
+            if (!path.StartsWith(subPath, StringComparison.OrdinalIgnoreCase)
+                || (!oldSubPathEndsWithSeparator && path[subPath.Length] != newDirectorySeparatorChar))
+            {
+                return false;
+            }
+
+            var newSubPathTrimmed = newSubPath.AsSpan().TrimEnd(newDirectorySeparatorChar);
+            // Ensure that the path with the old subpath removed starts with a leading dir separator
+            int idx = oldSubPathEndsWithSeparator ? subPath.Length - 1 : subPath.Length;
+            newPath = string.Concat(newSubPathTrimmed, path.AsSpan(idx));
+
+            return true;
+        }
     }
 }