/*_############################################################################
  _## 
  _##  SNMP4J-Agent 3 - TemporaryList.java  
  _## 
  _##  Copyright (C) 2005-2025  Frank Fock (SNMP4J.org)
  _##  
  _##  Licensed under the Apache License, Version 2.0 (the "License");
  _##  you may not use this file except in compliance with the License.
  _##  You may obtain a copy of the License at
  _##  
  _##      http://www.apache.org/licenses/LICENSE-2.0
  _##  
  _##  Unless required by applicable law or agreed to in writing, software
  _##  distributed under the License is distributed on an "AS IS" BASIS,
  _##  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  _##  See the License for the specific language governing permissions and
  _##  limitations under the License.
  _##  
  _##########################################################################*/

package org.snmp4j.agent.util;

import org.snmp4j.mp.SnmpConstants;

import java.util.LinkedList;
import java.util.Iterator;

/**
 * The {@code TemporaryList} implements a list whose items are automatically removed after a predefined timeout.
 * When an item is removed by timeout, listener can be called to handle the remove operation.
 *
 * @param <T> the type of the items held by this list.
 * @author Frank Fock
 */
public class TemporaryList<T> {

    // Default timeout is 5min.
    public static final int DEFAULT_ITEM_TIMEOUT = 300000;

    // default timeout for entries in 1/1000 seconds.
    private int timeout = DEFAULT_ITEM_TIMEOUT;
    private final LinkedList<TemporaryListItem<T>> list = new LinkedList<TemporaryListItem<T>>();

    public TemporaryList() {
    }

    /**
     * Creates a temporary list with the given timeout in milliseconds.
     *
     * @param timeout
     *         the milliseconds to wait before an entry may get removed from this list.
     */
    public TemporaryList(int timeout) {
        this.timeout = timeout;
    }

    public synchronized void add(T o) {
        long now = System.nanoTime();
        if ((!list.isEmpty()) &&
                ((list.getFirst()).atMaturity(now))) {
            list.removeFirst();
        }
        if ((!list.isEmpty()) &&
                ((list.getLast()).atMaturity(now))) {
            list.removeLast();
        }
        list.addFirst(new TemporaryListItem<T>(o));
    }

    public synchronized boolean contains(T o) {
        for (TemporaryListItem<?> item : list) {
            if (item.getItem().equals(o)) {
                return true;
            }
        }
        return false;
    }

    public synchronized boolean remove(T o) {
        long now = System.nanoTime();
        for (Iterator<TemporaryListItem<T>> it = list.iterator(); it.hasNext(); ) {
            TemporaryListItem<?> item = it.next();
            if (item.getItem().equals(o)) {
                it.remove();
                return true;
            } else if (item.atMaturity(now)) {
                it.remove();
            }
        }
        return false;
    }

    /**
     * Set the timeout for requests in this request list in milliseconds.
     * @param timeout
     *    a timeout value in milliseconds greater than zero.
     */
    public void setTimeout(int timeout) {
        if (timeout <= 0) {
            throw new IllegalArgumentException("Request list timeout millis must be > 0");
        }
        this.timeout = timeout;
    }

    /**
     * Get the timeout for requests in this list in milliseconds.
     * @return
     *    a timeout greater than zero in milliseconds.
     */
    public int getTimeout() {
        return timeout;
    }

    public Iterator<T> iterator() {
        return new TemporaryListIterator<T>(list);
    }

    public int size() {
        return list.size();
    }


    public synchronized void clear() {
        list.clear();
    }


    class TemporaryListItem<T> {
        private final T item;
        private final long timeOfMaturity;

        public TemporaryListItem(T item) {
            this.item = item;
            this.timeOfMaturity = System.nanoTime() + ((long) timeout * SnmpConstants.MILLISECOND_TO_NANOSECOND);
        }

        /**
         * Gets the time of maturity, i.e. the time in nano seconds when this entry may get removed earliest.
         *
         * @return the time of maturity in nanoseconds.
         */
        public long getTimeOfMaturity() {
            return timeOfMaturity;
        }

        public T getItem() {
            return item;
        }

        public boolean equals(Object obj) {
            return obj instanceof TemporaryList && item.equals(obj);
        }

        public int hashCode() {
            return item.hashCode();
        }

        /**
         * Checks if the given reference time in nanoseconds is later than the maturity time of this item.
         *
         * @param referenceTime
         *         the reference time in nanoseconds.
         *
         * @return {@code true} if the item is subject to removal from list,
         * {@code false} otherwise.
         */
        public boolean atMaturity(long referenceTime) {
            return (referenceTime > timeOfMaturity);
        }
    }

    class TemporaryListIterator<T> implements Iterator<T> {

        private final Iterator<TemporaryListItem<T>> iterator;

        public TemporaryListIterator(LinkedList<TemporaryListItem<T>> list) {
            iterator = list.iterator();
        }

        public boolean hasNext() {
            return iterator.hasNext();
        }

        public T next() {
            return iterator.next().getItem();
        }

        public void remove() {
            iterator.remove();
        }

    }
}
