pop-swap/swap.js

Range content change operator for arrays and array-like objects

"use strict";

// Copyright (C) 2014 Montage Studio
// https://github.com/montagejs/collections/blob/7c674d49c04955f01bbd2839f90936e15aceea2f/operators/swap.js

var array_slice = Array.prototype.slice;

module.exports = swap;
function swap(array, start, minusLength, plus) {
    // Unrolled implementation into JavaScript for a couple reasons.
    // Calling splice can cause large stack sizes for large swaps. Also,
    // splice cannot handle array holes.
    if (plus) {
        if (!Array.isArray(plus)) {
            plus = array_slice.call(plus);
        }
    } else {
        plus = Array.empty;
    }

    if (start < 0) {
        start = array.length + start;
    } else if (start > array.length) {
        array.length = start;
    }

    if (start + minusLength > array.length) {
        // Truncate minus length if it extends beyond the length
        minusLength = array.length - start;
    } else if (minusLength < 0) {
        // It is the JavaScript way.
        minusLength = 0;
    }

    var diff = plus.length - minusLength;
    var oldLength = array.length;
    var newLength = array.length + diff;

    if (diff > 0) {
        // Head Tail Plus Minus
        // H H H H M M T T T T
        // H H H H P P P P T T T T
        //         ^ start
        //         ^-^ minus.length
        //           ^ --> diff
        //         ^-----^ plus.length
        //             ^------^ tail before
        //                 ^------^ tail after
        //                   ^ start iteration
        //                       ^ start iteration offset
        //             ^ end iteration
        //                 ^ end iteration offset
        //             ^ start + minus.length
        //                     ^ length
        //                   ^ length - 1
        for (var index = oldLength - 1; index >= start + minusLength; index--) {
            var offset = index + diff;
            if (index in array) {
                array[offset] = array[index];
            } else {
                // Oddly, PhantomJS complains about deleting array
                // properties, unless you assign undefined first.
                array[offset] = void 0;
                delete array[offset];
            }
        }
    }
    for (var index = 0; index < plus.length; index++) {
        if (index in plus) {
            array[start + index] = plus[index];
        } else {
            array[start + index] = void 0;
            delete array[start + index];
        }
    }
    if (diff < 0) {
        // Head Tail Plus Minus
        // H H H H M M M M T T T T
        // H H H H P P T T T T
        //         ^ start
        //         ^-----^ length
        //         ^-^ plus.length
        //             ^ start iteration
        //                 ^ offset start iteration
        //                     ^ end
        //                         ^ offset end
        //             ^ start + minus.length - plus.length
        //             ^ start - diff
        //                 ^------^ tail before
        //             ^------^ tail after
        //                     ^ length - diff
        //                     ^ newLength
        for (var index = start + plus.length; index < oldLength - diff; index++) {
            var offset = index - diff;
            if (offset in array) {
                array[index] = array[offset];
            } else {
                array[index] = void 0;
                delete array[index];
            }
        }
    }
    array.length = newLength;
}