port from perforce

intromat/Intromat/Helpers/IOHelper.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Intromat.Helpers
+{
+    public static class IOHelper
+    {
+        public static string GetRelativePath(string basePath, string fullPath)
+        {
+            if (string.IsNullOrEmpty(basePath))
+                return fullPath ?? "";
+
+            if (string.IsNullOrEmpty(fullPath))
+                return "";
+
+            if (basePath.Last() != '\\')
+                basePath += "\\";
+
+            var builder = new StringBuilder(4096);
+            _ = PathRelativePathTo(builder, basePath, 0, fullPath, 0);
+            return builder.ToString()[2..];
+        }
+
+
+        [DllImport("shlwapi.dll", EntryPoint = "PathRelativePathTo", CharSet = CharSet.Unicode)]
+        private static extern bool PathRelativePathTo(StringBuilder lpszDst, string from, uint attrFrom, string to, uint attrTo);
+    }
+}