package com.alibaba.jstorm.utils;

import java.util.Deque;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.LinkedBlockingDeque;

/**
 * RotatingMap must be used under thread-safe environment
 * 
 * Expires keys that have not been updated in the configured number of seconds.
 * The algorithm used will take between expirationSecs and expirationSecs * (1 +
 * 1 / (numBuckets-1)) to actually expire the message.
 * 
 * get, put, remove, containsKey, and size take O(numBuckets) time to run.
 * 
 */
public class RotatingMap<K, V> implements TimeOutMap<K, V>{
	// this default ensures things expire at most 50% past the expiration time
	private static final int DEFAULT_NUM_BUCKETS = 3;


	private Deque<Map<K, V>> _buckets;

	private ExpiredCallback _callback;

	private final Object lock = new Object();

	public RotatingMap(int numBuckets, ExpiredCallback<K, V> callback, boolean isSingleThread) {
		if (numBuckets < 2) {
			throw new IllegalArgumentException("numBuckets must be >= 2");
		}
		if (isSingleThread == true) {
			_buckets = new LinkedList<Map<K, V>>();
		}else {
			_buckets = new LinkedBlockingDeque<Map<K, V>>();
		}
		
		for (int i = 0; i < numBuckets; i++) {
			_buckets.add(new ConcurrentHashMap<K, V>());
		}

		_callback = callback;
	}

	public RotatingMap(ExpiredCallback<K, V> callback) {
		this(DEFAULT_NUM_BUCKETS, callback, false);
	}

	public RotatingMap(int numBuckets) {
		this(numBuckets, null, false);
	}

	public Map<K, V> rotate() {
		Map<K, V> dead = _buckets.removeLast();
		_buckets.addFirst(new ConcurrentHashMap<K, V>());
		if (_callback != null) {
			for (Entry<K, V> entry : dead.entrySet()) {
				_callback.expire(entry.getKey(), entry.getValue());
			}
		}
		return dead;
	}

	@Override
	public boolean containsKey(K key) {
		for (Map<K, V> bucket : _buckets) {
			if (bucket.containsKey(key)) {
				return true;
			}
		}
		return false;
	}

	@Override
	public V get(K key) {
		for (Map<K, V> bucket : _buckets) {
			if (bucket.containsKey(key)) {
				return bucket.get(key);
			}
		}
		return null;
	}
	
	@Override
	public void putHead(K key, V value) {
		_buckets.peekFirst().put(key, value);
	}

	@Override
	public void put(K key, V value) {
		Iterator<Map<K, V>> it = _buckets.iterator();
		Map<K, V> bucket = it.next();
		bucket.put(key, value);
		while (it.hasNext()) {
			bucket = it.next();
			bucket.remove(key);
		}
	}


	/**
	 * Remove item from Rotate
	 * 
	 * On the side of performance, scanning from header is faster On the side of
	 * logic, it should scan from the end to first.
	 * 
	 * @param key
	 * @return
	 */
	@Override
	public Object remove(K key) {
		for (Map<K, V> bucket : _buckets) {
			Object value = bucket.remove(key);
			if (value != null) {
				return value;
			}
		}
		return null;
	}

	@Override
	public int size() {
		int size = 0;
		for (Map<K, V> bucket : _buckets) {
			size += bucket.size();
		}
		return size;
	}
}
