var bases = require('bases');
var crypto = require('crypto');

// Returns a base-62 (alphanumeric only) string of the given length:
function randomStr(length) {
    // We generate a random number in a space at least as big as 62^length,
    // and if it's too big, we just retry. This is still statistically O(1)
    // since repeated probabilities less than one converge to zero. Hat-tip to
    // a Google interview for teaching me this technique! ;)

    // The native randomBytes() returns an array of bytes, each of which is
    // effectively a base-256 integer. We derive the number of bytes to
    // generate based on that, but note that it can overflow after ~150:
    var maxNum = Math.pow(62, length);
    var numBytes = Math.ceil(Math.log(maxNum) / Math.log(256));
    if (numBytes === Infinity) {
        throw new Error('Length too large; caused overflow: ' + length);
    }

    do {
        var bytes = crypto.randomBytes(numBytes);
        var num = 0
        for (var i = 0; i < bytes.length; i++) {
            num += Math.pow(256, i) * bytes[i];
        }
    } while (num >= maxNum);

    return bases.toBase62(num);
}

for (var i = 1; i < 80; i++) {
    console.log(randomStr(i));
}