data-structures-and-algorithms/deque

import ArbitrarySizeDeque from './ArbitrarySizeDeque.js';

/**
 * BoundedDeque.
 *
 * @param {Iterable<any>} iterable
 * @param {Number} maxlen
 */
export default function BoundedDeque(iterable, maxlen) {
    this._maxlen = maxlen;

    // eslint-disable-next-line unicorn/no-new-array
    this._container = new Array(maxlen);

    this._center = 0;

    this.length = 0;

    if (iterable !== null) {
        this.extend(iterable);
    }
}

BoundedDeque.prototype = new ArbitrarySizeDeque();

BoundedDeque.prototype.len = function () {
    return this.length;
};

BoundedDeque.prototype.capacity = function () {
    return this._maxlen;
};

BoundedDeque.prototype.append = function (x) {
    if (this.length === this._maxlen) {
        this._container[this._center] = x;
        ++this._center;
        this._center %= this._maxlen;
    } else {
        const i = (this._center + this.length) % this._maxlen;
        this._container[i] = x;
        ++this.length;
    }

    return this;
};

BoundedDeque.prototype.appendleft = function (x) {
    --this._center;
    this._center += this._maxlen;
    this._center %= this._maxlen;
    this._container[this._center] = x;

    if (this.length < this._maxlen) {
        ++this.length;
    }

    return this;
};

BoundedDeque.prototype.clear = function () {
    this._center = 0;

    this.length = 0;

    // eslint-disable-next-line unicorn/no-new-array
    this._container = new Array(this._maxlen);

    return this;
};

BoundedDeque.prototype.copy = function () {
    return new BoundedDeque(this, this._maxlen);
};

BoundedDeque.prototype._where = function (i) {
    this._checkbounds(i);

    return [this._container, (this._center + i) % this._maxlen];
};

/**
 * BoundedDeque.prototype._popindex.
 *
 * @param {any} container
 * @param {Number} index
 * @return {any}
 */
BoundedDeque.prototype._popindex = function (container, index) {
    const value = container[index];

    // GC
    // TODO use null instead of 0 for non-Number deques
    container[index] = 0;

    --this.length;

    return value;
};