// Version 1, use sleep
/**
 * public class HtmlHelper {
 *     public static List<String> parseUrls(String url);
 *         // Get all urls from a webpage of given url. 
 * }
*/
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.lang.Thread;
import java.net.*;
import java.io.*;

class CrawlerThread extends Thread {
    private static BlockingQueue<String> queue = new LinkedBlockingQueue<String>();

    private static HashMap<String, Boolean> mp = new HashMap<String, Boolean>();
    private static List<String> results = new ArrayList<String>();

    public static void setFirstUrl(String url) {
        try {
            queue.put(url);
        } catch (InterruptedException e) {
            // e.printStackTrace(); 
        }
    }

    public static List<String> getResults() {
        return results;
    }

    @Override
    public void run() {
        while (true) {
            String url = "";
            try {
                url = queue.take();
            } catch (Exception e) {
                // e.printStackTrace(); 
                break;
            }

            String domain = "";
            try {
                URL netUrl = new URL(url);
                domain = netUrl.getHost();
            } catch (MalformedURLException e) {
                // e.printStackTrace(); 
            }
            if (!mp.containsKey(url) && domain.endsWith("wikipedia.org")) {
                mp.put(url, true);
                results.add(url);
                List<String> urls = HtmlHelper.parseUrls(url);
                for (String u : urls) {
                    try {
                        queue.put(u);
                    } catch (InterruptedException e) {
                        // e.printStackTrace(); 
                    }
                }
            }
        }
    }
}

public class Solution {
    /**
     * @param url a url of root page
     * @return all urls
     */
    public List<String> crawler(String url) {
        // Write your code here
        CrawlerThread.setFirstUrl(url);
        CrawlerThread[] thread_pools = new CrawlerThread[7];
        for (int i = 0; i < 3; ++i) {
            thread_pools[i] = new CrawlerThread();
            thread_pools[i].start();
        }

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e){
            // e.printStackTrace();
        }

        for (int i = 0; i < 3; ++i) {
            //thread_pools[i].interrupt();
            thread_pools[i].stop();
        }

        List<String> results = CrawlerThread.getResults();
        return results;
    }
}


// Version 2, use AtomicLong
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicLong;
import java.lang.Thread;
import java.net.*;
import java.io.*;


class CrawlerThread extends Thread {
    private static AtomicLong counter;
    private static BlockingQueue<String> queue = new LinkedBlockingQueue<String>();

    private static HashMap<String, Boolean> mp = new HashMap<String, Boolean>();
    private static List<String> results = new ArrayList<String>();

    public static void setFirstUrl(String url, int thread_num) {
        counter = new AtomicLong(thread_num);

        try {
            queue.put(url);
        } catch (InterruptedException e) {
            // e.printStackTrace(); 
        }
    }

    public static Long getCounter() {
        return counter.get();
    }

    public static List<String> getResults() {
        return results;
    }

    @Override
    public void run() {
        while (true) {
            String url = "";
            try {
                counter.decrementAndGet();
                url = queue.take();
                counter.incrementAndGet();
            } catch (Exception e) {
                // e.printStackTrace(); 
                break;
            }

            String domain = "";
            try {
                URL netUrl = new URL(url);
                domain = netUrl.getHost();
            } catch (MalformedURLException e) {
                // e.printStackTrace(); 
            }
            if (!mp.containsKey(url) && domain.endsWith("wikipedia.org")) {
                mp.put(url, true);
                results.add(url);
                List<String> urls = HtmlHelper.parseUrls(url);
                for (String u : urls) {
                    try {
                        queue.put(u);
                    } catch (InterruptedException e) {
                        // e.printStackTrace(); 
                    }
                }
            }
        }
    }
}

public class Solution {
    /**
     * @param url a url of root page
     * @return all urls
     */
    public List<String> crawler(String url) {
        // Write your code here
        int thread_num = 3;
        CrawlerThread.setFirstUrl(url, thread_num);

        CrawlerThread[] thread_pools = new CrawlerThread[thread_num];
        for (int i = 0; i < thread_num; ++i) {
            thread_pools[i] = new CrawlerThread();
            thread_pools[i].start();
        }

        while (CrawlerThread.getCounter() > 0);

        for (int i = 0; i < thread_num; ++i) {
            thread_pools[i].stop();
        }

        List<String> results = CrawlerThread.getResults();
        return results;
    }
}