package org.simantics.db.layer0.variable;

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;

import gnu.trove.map.hash.TObjectLongHashMap;

/**
 * @author Antti Villberg
 *
 * @param <Node>
 * @param <Value>
 * 
 * @since 1.23
 */
public class NodeCache<Node,Value> {

	// Expiration time for items in this cache
	private long defaultExpirationTimeInNs;

	// Here we hold all nodes with finite expiration times
	private TreeMap<Long,Node> expirationTimes = new TreeMap<Long,Node>();
	// Finite expiration times for nodes
	private TObjectLongHashMap<Node> exp = new TObjectLongHashMap<Node>(10, 0.5f, -1L);
	
	// All node values
	private Map<Node,Value> map = new HashMap<Node,Value>();

	private boolean disposed;

	public NodeCache() {
		this(1_000_000_000L);
	}

	public NodeCache(long defaultExpirationTimeInNs) {
		this.defaultExpirationTimeInNs = defaultExpirationTimeInNs;
	}

	public synchronized Value get(Node node) {
		return map.get(node); 
	}
	
	public synchronized void clearExpired() {
		
		long now = System.nanoTime();
		while(!expirationTimes.isEmpty()) {
			Long first = expirationTimes.firstKey();
			if(first < now) {
				Node node = expirationTimes.remove(first);
				exp.remove(node);
				map.remove(node);
			} else {
				return;
			}
		}
		
	}

	private long scheduleExpiration(Node node, long expiration) {
		while(expirationTimes.containsKey(expiration)) expiration++;
		expirationTimes.put(expiration, node);
		exp.put(node, expiration);
		return expiration;
	}
	
	private void refreshExpiration(Node node, long newExpiration, boolean existing) {
		
		long current = exp.get(node);
		if(current == -1) {
			if(existing) {
				// We have infinite expiration => do nothing
			} else {
				// This is a new value
				if(newExpiration == 0) {
					// We require infinite expiration => do nothing
				} else {
					scheduleExpiration(node, newExpiration);
				}
			}
			return;
		}
		
		// This node is already under expiration tracking
		if(newExpiration == 0) {
			// We now want infinite expiration => remove expiration time info
			expirationTimes.remove(current);
			exp.remove(node);
		} else {
			if(newExpiration > current) {
				// Update expiration time
				expirationTimes.remove(current);
				scheduleExpiration(node, newExpiration);
			}
		}
		
	}

	public synchronized void put(Node node, Value value) {
		if (disposed)
			return;
		Value existing = map.put(node, value);
		refreshExpiration(node, 0, existing != null);
	}

	public synchronized void put(Node node, Value value, long expiration) {
		if (disposed)
			return;
		Value existing = map.put(node, value);
		refreshExpiration(node, System.nanoTime() + expiration, existing != null);
	}

	public synchronized void removeListening(Node node) {
		if (disposed)
			return;
		scheduleExpiration(node, System.nanoTime() + defaultExpirationTimeInNs);
	}

	public synchronized void dispose() {
		disposed = true;
		expirationTimes.clear();
		exp.clear();
		map.clear();
	}
	
}