1 files changed, 85 insertions, 13 deletions

diff --git a/Emby.Server.Implementations/Library/PathExtensions.cs b/Emby.Server.Implementations/Library/PathExtensions.cs
index d3a81f622..d5b855cdf 100644
--- a/Emby.Server.Implementations/Library/PathExtensions.cs
+++ b/Emby.Server.Implementations/Library/PathExtensions.cs
@@ -1,45 +1,117 @@
 using System;
-using System.Text.RegularExpressions;
+using System.Diagnostics.CodeAnalysis;
+using MediaBrowser.Common.Providers;
 
 namespace Emby.Server.Implementations.Library
 {
+    /// <summary>
+    /// Class providing extension methods for working with paths.
+    /// </summary>
     public static class PathExtensions
     {
         /// <summary>
         /// Gets the attribute value.
         /// </summary>
         /// <param name="str">The STR.</param>
-        /// <param name="attrib">The attrib.</param>
+        /// <param name="attribute">The attrib.</param>
         /// <returns>System.String.</returns>
-        /// <exception cref="ArgumentNullException">attrib</exception>
-        public static string GetAttributeValue(this string str, string attrib)
+        /// <exception cref="ArgumentException"><paramref name="str" /> or <paramref name="attribute" /> is empty.</exception>
+        public static string? GetAttributeValue(this string str, string attribute)
         {
-            if (string.IsNullOrEmpty(str))
+            if (str.Length == 0)
             {
-                throw new ArgumentNullException(nameof(str));
+                throw new ArgumentException("String can't be empty.", nameof(str));
             }
 
-            if (string.IsNullOrEmpty(attrib))
+            if (attribute.Length == 0)
             {
-                throw new ArgumentNullException(nameof(attrib));
+                throw new ArgumentException("String can't be empty.", nameof(attribute));
             }
 
-            string srch = "[" + attrib + "=";
+            string srch = "[" + attribute + "=";
             int start = str.IndexOf(srch, StringComparison.OrdinalIgnoreCase);
-            if (start > -1)
+            if (start != -1)
             {
                 start += srch.Length;
                 int end = str.IndexOf(']', start);
                 return str.Substring(start, end - start);
             }
+
             // for imdbid we also accept pattern matching
-            if (string.Equals(attrib, "imdbid", StringComparison.OrdinalIgnoreCase))
+            if (string.Equals(attribute, "imdbid", StringComparison.OrdinalIgnoreCase))
             {
-                var m = Regex.Match(str, "tt\\d{7}", RegexOptions.IgnoreCase);
-                return m.Success ? m.Value : null;
+                var match = ProviderIdParsers.TryFindImdbId(str, out var imdbId);
+                return match ? imdbId.ToString() : null;
             }
 
             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(
+            [NotNullWhen(true)] this string? path,
+            [NotNullWhen(true)] string? subPath,
+            [NotNullWhen(true)] 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))
+            {
+                return false;
+            }
+
+            if (path.Length > subPath.Length
+                && !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;
+        }
     }
 }