module.exports = shuffle;

/*

shuffle([1, 2, 3]);

// array with original elements randomly sorted

shuffle([1, 2, 3], {shuffleAll: true});

// array with original elements randomly sorted and all in a new position

shuffle([1]); // [1]

shuffle(); // throws

shuffle(undefined); // throws

shuffle(null); // throws

shuffle({}); // throws

*/

function shuffle(arr, options) {

if (!Array.isArray(arr)) {

throw new Error('expected an array');

}

if (arr.length < 2) {

return arr;

}

var shuffleAll = options && options.shuffleAll;

var result = arr.slice();

var i = arr.length, rand, temp;

while (--i > 0) {

do {

rand = Math.floor(Math.random() * (i + 1));

} while (shuffleAll && rand == i);

if (!shuffleAll || rand != i) {

temp = result[i];

result[i] = result[rand];

result[rand] = temp;

}

}

return result;

}