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There is a newer version: 2.1.0-alpha1

package org.slf4j.helpers;

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.HashMap;
import java.util.Map;


/**
 * A simple implementation of ThreadLocal backed Map containing values of type 
 * Deque.
 * 
 * @author Ceki Guuml;cü
 * @since 2.0.0
 */
public class ThreadLocalMapOfStacks {

    final ThreadLocal>> tlMapOfStacks = new ThreadLocal<>();

    public void pushByKey(String key, String value) {
        if (key == null)
            return;

        Map> map = tlMapOfStacks.get();

        if (map == null) {
            map = new HashMap<>();
            tlMapOfStacks.set(map);
        }

        Deque deque = map.get(key);
        if (deque == null) {
            deque = new ArrayDeque<>();
        }
        deque.push(value);
        map.put(key, deque);
    }

    public String popByKey(String key) {
        if (key == null)
            return null;

        Map> map = tlMapOfStacks.get();
        if (map == null)
            return null;
        Deque deque = map.get(key);
        if (deque == null)
            return null;
        return deque.pop();
    }

    public Deque getCopyOfDequeByKey(String key) {
        if (key == null)
            return null;

        Map> map = tlMapOfStacks.get();
        if (map == null)
            return null;
        Deque deque = map.get(key);
        if (deque == null)
            return null;

        return new ArrayDeque(deque);
    }
    
    /**
     * Clear the deque(stack) referenced by 'key'. 
     * 
     * @param key identifies the  stack
     * 
     * @since 2.0.0
     */
    public void clearDequeByKey(String key) {
        if (key == null)
            return;

        Map> map = tlMapOfStacks.get();
        if (map == null)
            return;
        Deque deque = map.get(key);
        if (deque == null)
            return;
        deque.clear();
    }

}