list-abstraction/specification

import assert from 'assert';

import Node from './Node.js';

export default class ReverseIterator {
    /**
     * @param {Node[]} array
     * @param {Node} current
     */
    constructor(array, current) {
        assert(current instanceof Node);
        this.array = array;
        this.current = current;
    }

    copy() {
        return new ReverseIterator(this.array, this.current);
    }

    next() {
        const i = this.array.indexOf(this.current);
        this.current = this.array[i - 1];
        if (this.current === this.array[0]) {
            return {done: true};
        }

        return {
            value: this.current.value,
            done: false,
        };
    }

    prev() {
        const i = this.array.indexOf(this.current);
        this.current = this.array[i + 1];
        if (this.current === this.array.at(-1)) {
            return {done: true};
        }

        return {
            value: this.current.value,
            done: false,
        };
    }
}