#!/usr/bin/java --source 11
import java.io.IOException; import java.nio.file.*; import java.nio.file.attribute.BasicFileAttributes;
public class Main {
    /** @param args directory, sourcePrefix, targetPrefix */
    public static void main(String[] args) throws IOException {
        Path dir = Path.of(args[0]).toAbsolutePath().normalize();
        Path sourcePrefix = dir.resolve(Path.of(args[1])).normalize();
        Path targetPrefix = dir.resolve(Path.of(args[2])).normalize();
        System.out.printf("Replacing symlinks in '%s' from '%s' to '%s'%n", dir, sourcePrefix, targetPrefix);
        Files.walkFileTree(dir, new SimpleFileVisitor<>() {
            @Override public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
                if (attrs.isSymbolicLink()) {
                    var originalTarget = Files.readSymbolicLink(file).normalize();
                    if (originalTarget.startsWith(sourcePrefix)) {
                        var symlinkFileDir = file.getParent();
                        originalTarget = symlinkFileDir.resolve(originalTarget);
                        Files.delete(file);
                        var target = symlinkFileDir.relativize(targetPrefix.resolve(sourcePrefix.relativize(originalTarget))).normalize();
                        Files.createSymbolicLink(file, target);
                        System.out.printf("Symlink at '%s' pointing at '%s' is now pointing at '%s'%n", file, originalTarget, target);
                    }
                }
                return FileVisitResult.CONTINUE;
            }
        });
    }
}