private static string GetRelativePath(string relativeTo, string path, StringComparison comparisonType)
{
if (string.IsNullOrEmpty(relativeTo))
{
throw new ArgumentNullException(nameof(relativeTo));
}
if (string.IsNullOrWhiteSpace(path))
{
throw new ArgumentNullException(nameof(path));
}
Debug.Assert(comparisonType == StringComparison.Ordinal || comparisonType == StringComparison.OrdinalIgnoreCase);
relativeTo = GetFullPath(relativeTo);
path = GetFullPath(path);
// Need to check if the roots are different- if they are we need to return the "to" path.
if (!PathInternal.AreRootsEqual(relativeTo, path, comparisonType))
{
return(path);
}
int commonLength = PathInternal.GetCommonPathLength(relativeTo, path, ignoreCase: comparisonType == StringComparison.OrdinalIgnoreCase);
// If there is nothing in common they can't share the same root, return the "to" path as is.
if (commonLength == 0)
{
return(path);
}
// Trailing separators aren't significant for comparison
int relativeToLength = relativeTo.Length;
if (PathInternal.EndsInDirectorySeparator(relativeTo))
{
relativeToLength--;
}
bool pathEndsInSeparator = PathInternal.EndsInDirectorySeparator(path);
int pathLength = path.Length;
if (pathEndsInSeparator)
{
pathLength--;
}
// If we have effectively the same path, return "."
if (relativeToLength == pathLength && commonLength >= relativeToLength)
{
return(".");
}
// We have the same root, we need to calculate the difference now using the
// common Length and Segment count past the length.
//
// Some examples:
//
// C:\Foo C:\Bar L3, S1 -> ..\Bar
// C:\Foo C:\Foo\Bar L6, S0 -> Bar
// C:\Foo\Bar C:\Bar\Bar L3, S2 -> ..\..\Bar\Bar
// C:\Foo\Foo C:\Foo\Bar L7, S1 -> ..\Bar
StringBuilder sb = StringBuilderCache.Acquire(Math.Max(relativeTo.Length, path.Length));
// Add parent segments for segments past the common on the "from" path
if (commonLength < relativeToLength)
{
sb.Append(PathInternal.ParentDirectoryPrefix);
for (int i = commonLength; i < relativeToLength; i++)
{
if (PathInternal.IsDirectorySeparator(relativeTo[i]))
{
sb.Append(PathInternal.ParentDirectoryPrefix);
}
}
}
else if (PathInternal.IsDirectorySeparator(path[commonLength]))
{
// No parent segments and we need to eat the initial separator
// (C:\Foo C:\Foo\Bar case)
commonLength++;
}
// Now add the rest of the "to" path, adding back the trailing separator
int count = pathLength - commonLength;
if (pathEndsInSeparator)
{
count++;
}
sb.Append(path, commonLength, count);
return(StringBuilderCache.GetStringAndRelease(sb));
}
