package com.dfsn.cloud.eureka;

public class BothwayLinkedList<T> {
    // 头节点
    private Node first;

    // 尾节点
    private Node last;

    // 元素个数
    private int size = 0;

    // 增加元素
    public void add(T t) {
        if (first == null) {
            Node newNode = new Node(t, null, null);
            first = newNode;
            last = newNode;
        } else {
            Node newLast = new Node(t, null, last);
            last.next = newLast;
            last = newLast;
        }
        size++;
    }

    // 返回元素个数
    public int size() {
        return size;
    }

    // 遍历链表
    public void show() {
        if (first == null) {
            throw new RuntimeException("链表为空");
        } else {
            Node temp = first;
            while (true) {
                System.out.println(temp);
                if (temp.next == null) {
                    break;
                }
                temp = temp.next;
            }

        }
    }

    // 根据下标获取节点
    public T get(int index) {
        return get(index, "").item;
    }

    private Node get(int index, String s) {
        if (first == null) {
            throw new RuntimeException("链表为空，没有对应节点");
        } else if (index >= size) {
            throw new RuntimeException("链表长度为：" + size + ",index为" + (size - 1));
        } else if (index < 0) {
            throw new RuntimeException("下标不能<0");
        } else {
            int avg = size / 2;
            if (index < avg) {
                Node temp = first;
                for (int i = 0; i < index; i++) {
                    temp = temp.next;
                }
                return temp;
            } else {
                Node temp = last;
                for (int i = size - 1; i > index; i--) {
                    temp = temp.prev;
                }
                return temp;
            }
        }
    }

    // 在指定位置插入
    public void add(int index, T t) {
        if (index > size) {
            throw new RuntimeException("链表长度为：" + size + ",index为" + size);
        } else if (index < 0) {
            throw new RuntimeException("下标不能<0");
        } else if (index == 0) {
            Node newNode = new Node(t, first, null);
            newNode.next = first;
            first = newNode;
        } else if (index == size) {
            Node newNode = new Node(t, null, last);
            last.next = newNode;
            last = newNode;
        } else {
            // 原来位置的node
            Node node = get(index, "");
            Node newNode = new Node(t, node, node.prev);
            node.prev.next = newNode;
            node.prev = newNode;
        }
        size++;
    }

    // 更改指定位置的元素
    public void set(int index, T t) {
        if (index >= size) {
            throw new RuntimeException("链表长度为：" + size + ",index为" + (size - 1));
        } else if (index < 0) {
            throw new RuntimeException("下标不能<0");
        } else {
            Node node = get(index, "");
            node.item = t;
        }
    }

    // 删除指定位置的元素
    public void remove(int index) {
        if (index >= size) {
            throw new RuntimeException("链表长度为：" + size + ",index为" + (size - 1));
        } else if (index < 0) {
            throw new RuntimeException("下标不能<0");
        } else if (index == 0) {
            first = first.next;
            first.prev = null;
        } else if (index == size - 1) {
            last = last.prev;
            last.next = null;
        } else {
            Node node = get(index, "");
            Node next = node.next;
            Node prev = node.prev;
            prev.next = next;
            next.prev = prev;
        }
        size--;
    }

    // 返回头节点
    public T getFirst() {
        return first.item;
    }

    // 返回尾节点
    public T getLasts() {
        return last.item;
    }

    // 节点对象
    class Node {
        private T item;
        private Node next;
        private Node prev;

        public Node(T item, Node next, Node prev) {
            this.item = item;
            this.next = next;
            this.prev = prev;
        }

        @Override
        public String toString() {
            return "Node [item=" + item + "]";
        }

    }
}