/*-
    * #%L
    * io.earcam.instrumental.io
    * %%
    * Copyright (C) 2018 earcam
    * %%
    * SPDX-License-Identifier: (BSD-3-Clause OR EPL-1.0 OR Apache-2.0 OR MIT)
    * 
    * You <b>must</b> choose to accept, in full - any individual or combination of 
   * the following licenses:
   * <ul>
   * 	<li><a href="https://opensource.org/licenses/BSD-3-Clause">BSD-3-Clause</a></li>
   * 	<li><a href="https://www.eclipse.org/legal/epl-v10.html">EPL-1.0</a></li>
   * 	<li><a href="https://www.apache.org/licenses/LICENSE-2.0">Apache-2.0</a></li>
   * 	<li><a href="https://opensource.org/licenses/MIT">MIT</a></li>
   * </ul>
   * #L%
   */
  package io.earcam.utilitarian.io;
  
  import java.nio.file.DirectoryStream;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.util.ArrayDeque;
  import java.util.Deque;
  import java.util.Iterator;
  import java.util.function.Function;
  
  import io.earcam.unexceptional.Exceptional;
  
  class RecursivePathIterator implements Iterator<Path> {
  
  	private static final Function<Path, DirectoryStream<Path>> DEFAULT_STREAMER = Exceptional.uncheckFunction(Files::newDirectoryStream);
  	private final Deque<Iterator<Path>> pending = new ArrayDeque<>();
  	private final Function<Path, DirectoryStream<Path>> streamer;
  	private Iterator<Path> current;
  
  
  	RecursivePathIterator(Path root)
  	{
  		this(root, DEFAULT_STREAMER);
  	}
  
  
  	RecursivePathIterator(Path root, Function<Path, DirectoryStream<Path>> directoryStreamer)
  	{
  		this(directoryStreamer.apply(root).iterator(), directoryStreamer);
  	}
  
  
  	RecursivePathIterator(Iterator<Path> iterator, Function<Path, DirectoryStream<Path>> directoryStreamer)
  	{
  		this.current = iterator;
  		this.streamer = directoryStreamer;
  	}
  
  
  	@Override
  	public boolean hasNext()
  	{
  		return current.hasNext()
  				|| popPending();
  	}
  
  
  	private boolean popPending()
  	{
  		if(pending.isEmpty()) {
  			return false;
  		}
  		current = pending.pop();
  		return hasNext();
  	}
  
  
  	@Override
  	public Path next()
  	{
  		Path next = current.next();
  		if(next.toFile().isDirectory()) {
  			pending.push(current);
  			current = streamer.apply(next).iterator();
  		}
  		return next;
  	}
  
  }