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package com.github.jy2.di.monitor;

import static java.nio.file.StandardWatchEventKinds.OVERFLOW;

import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.ArrayList;
import java.util.function.Consumer;

import static java.nio.file.StandardWatchEventKinds.*;

public class DirectoryMonitor {
	ArrayList> consumers = new ArrayList>();
	boolean keepRunning = true;
	WatchService watcher;
	Thread thread;
	WatchKey key;

	public void monitor(Path path) throws IOException {
		watcher = FileSystems.getDefault().newWatchService();
		thread = new Thread(() -> {
			while (keepRunning) {
				WatchKey key;
				try {
					key = watcher.take();
				} catch (InterruptedException x) {
					continue;
				}

				for (WatchEvent event : key.pollEvents()) {
					WatchEvent.Kind kind = event.kind();

					if (kind == OVERFLOW) {
						continue;
					}

					WatchEvent ev = (WatchEvent) event;
					Path filename = ev.context();
					updateConsumers(filename.toString());
				}

				boolean valid = key.reset();
				if (!valid) {
					break;
				}

			}
		}, "DirectoryMonitor");
		thread.start();
		key = path.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
	}

	public synchronized void addListener(Consumer consumer) {
		consumers.add(consumer);
	}

	public synchronized void stop() {
		consumers.clear();
		keepRunning = false;
		if (key != null) {
			key.cancel();
		}
		thread.interrupt();
	}

	private synchronized void updateConsumers(String filename) {
		for (Consumer c : consumers) {
			c.accept(filename);
		}
	}

}