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/*
 Licensed to Diennea S.r.l. under one
 or more contributor license agreements. See the NOTICE file
 distributed with this work for additional information
 regarding copyright ownership. Diennea S.r.l. licenses this file
 to you 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 herddb.utils;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * Combined strucutre linked list / hash map.
 * 
 * If necessary elements can be removed in O1 with {@link #remove(Object)}
 * 
 *
 * @param 
 * @author diego.salvi
 */
public class ListWithMap {

    /**
     * Pointer to first node.
     * Invariant: (head == null && tail == null) ||
     * (head.prev == null && head.item != null)
     */
    private Node head;

    /**
     * Pointer to last node.
     * Invariant: (head == null && tail == null) ||
     * (tail.next == null && tail.item != null)
     */
    private Node tail;

    private Map> space;

    public ListWithMap() {

        head = tail = null;

        space = new HashMap<>();
    }

    public void append(E e) {
        final Node ref = tail;
        final Node node = new Node<>(ref, e, null);
        tail = node;

        if (ref == null) {
            head = node;
        } else {
            ref.next = node;
        }

        space.put(e, node);
    }

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

    public boolean isEmpty() {
        return space.isEmpty();
    }

    public E peek() {
        final Node ref = head;
        return (ref == null) ? null : ref.item;
    }

    public E poll() {

        final Node ref = head;

        if (ref == null) {
            return null;
        }

        final E result = ref.item;
        final Node next = ref.next;

        ref.item = null;
        ref.prev = null;
        ref.next = null;

        head = next;

        if (next == null) {
            tail = null;
        } else {
            next.prev = null;
        }

        space.remove(result);

        return result;
    }

    public boolean contains(E e) {
        return space.containsKey(e);
    }

    public E remove(E e) {

        final Node ref = space.remove(e);

        if (ref == null) {
            return null;
        }

        if (ref.prev == null) {
            /* E' la testa */
            head = ref.next;
        } else {
            ref.prev.next = ref.next;
        }

        if (ref.next == null) {
            /* E' la coda */
            tail = ref.prev;
        } else {
            ref.next.prev = ref.prev;
        }

        final E rem = ref.item;

        ref.item = null;
        ref.prev = null;
        ref.next = null;

        return rem;
    }

    public void clear() {

        Node ref = head;
        while (ref != null) {
            Node next = ref.next;

            ref.item = null;
            ref.prev = null;
            ref.next = null;

            ref = next;
        }

        space.clear();
    }

    private static class Node {
        E item;
        Node prev;
        Node next;

        Node(Node prev, E element, Node next) {
            this.item = element;
            this.prev = prev;
            this.next = next;
        }
    }

    public List toList() {


        final List list = new ArrayList<>(space.size());

        Node ref = head;
        while (ref != null) {
            list.add(ref.item);
            ref = ref.next;
        }

        return list;

    }
}