import EventEmitter from 'events';

class Node {
    constructor(data) {
        this._data = data;
        this._next = null;
    }

    get data() {
        return this._data;
    }

    get next() {
        return this._next;
    }

    set next(val) {
        this._next = val;
    }
}

class Queue extends EventEmitter {
    constructor(initDatas = [], maxSize = 0) {
        super();
        EventEmitter.call(this);

        this._front = null;
        this._tail = null;
        this._size = 0;
        this._maxSize = maxSize;

        for (const d of initDatas) {
            this.enque(d);
        }
    }

    push(data) {
        const node = new Node(data);

        if (!this._tail) {
            this._front = node;
            this._tail = node;
        } else {
            this._tail.next = node;
            this._tail = node;
        }

        this._size += 1;

        if (this._maxSize > 0 && this._size > this._maxSize) {
            this.pop();
        }

        this.emit('pushed');
        return this._size;
    }

    pop() {
        if (!this._front || this._size === 0) return null;

        const node = this._front;
        this._front = this._front.next;
        if (!this._front) {
            this._tail = null;
        }
        this._size = Math.max(0, this._size - 1);
        return node.data;
    }

    clear() {
        while (this.size() > 0) {
            this.pop();
        }
    }

    size() {
        return Math.max(0, this._size);
    }
}

export default Queue;