methods to coerce one file system directory "into" another

coerceTo.kt

    /**
     * make `targetToModify` identical to `source` in as few changes as possible.
     */
    @JvmStatic fun coerceTo(source: Path, targetToModify: Path){
        NIOFiles.walkFileTree(targetToModify, PruneByComparisonFileVisitor(source, targetToModify))
        NIOFiles.walkFileTree(source, AddByComparisonFileVisitor(source, targetToModify))
    }

    infix fun Int.pow(power: Int) = Math.pow(this.toDouble(), power.toDouble()).toInt()

    class PruneByComparisonFileVisitor(val reference: Path, val targetToModify: Path) : FileVisitor<Path> {

        override fun preVisitDirectory(dir: Path, attrs: BasicFileAttributes): FileVisitResult {

            val relativePath = dir relativeTo targetToModify

            if(relativePath.isEmpty){ return CONTINUE }

            if((reference / relativePath).nodeEquals(dir)){ return CONTINUE }

            FileUtils.deleteDirectory(dir.toFile())

            return FileVisitResult.SKIP_SUBTREE
        }

        override fun postVisitDirectory(dir: Path, exc: IOException?) = CONTINUE

        override fun visitFile(file: Path, attrs: BasicFileAttributes?): FileVisitResult {
            val relativePath = file relativeTo targetToModify

            //remember, the copy structure will replace older files with newer ones,
            //we're only interested in deleting files.

            if((reference / relativePath).nodeEquals(file)) { return CONTINUE }

            NIOFiles.delete(file);

            return CONTINUE
        }

        override fun visitFileFailed(file: Path, exc: IOException?) = CONTINUE
    }

    class AddByComparisonFileVisitor(val reference: Path, val targetToModify: Path) : FileVisitor<Path> {

        override fun preVisitDirectory(dir: Path, attrs: BasicFileAttributes): FileVisitResult {
            val relativePath = dir relativeTo reference

            if(relativePath.isEmpty){ return CONTINUE }

            val pathOnTarget = targetToModify / relativePath

            if( ! pathOnTarget.nodeEquals(dir)){
                NIOFiles.createDirectory(pathOnTarget)
            }

            return CONTINUE
        }

        override fun visitFileFailed(file: Path, exc: IOException?): FileVisitResult {
            return CONTINUE;
        }

        override fun postVisitDirectory(dir: Path, exc: IOException?): FileVisitResult {
            return CONTINUE;
        }

        override fun visitFile(file: Path, attrs: BasicFileAttributes): FileVisitResult {
            val target = targetToModify / (file relativeTo reference)

            //TODO cache this? this is going to copy a lot of files over top of exact copies of those files.
            FileUtils.copyFile(file.toFile(), target.toFile())

            return CONTINUE;
        }

    }

    fun Path.nodeEquals(other: Path): Boolean {

        return (NIOFiles.exists(this) == NIOFiles.exists(other))
                && (this.fileName == other.fileName)
                && (NIOFiles.isDirectory(this) == NIOFiles.isDirectory(other))
                && (NIOFiles.isRegularFile(this) == NIOFiles.isRegularFile(other))
    }