random-position/dist/index.js

Generate random positions for ordered sequences

'use strict';

var base = " !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~";

function between(a, b) {
  if (a === undefined) return before(b);
  if (b === undefined) return after(a);

  if (a === b) {
    throw new Error('The numbers must be different');
  }

  if (a > b) {
    throw new Error('The numbers are not in the correct order');
  }

  var result = '';
  var position = 0;
  var carry = null;
  var count = 0;

  while (true) {
    var aindex = toNumber(a[position]);
    var bindex = toNumber(b[position]);

    if (carry !== null) bindex += base.length;

    if (aindex === bindex) {
      result += toString(aindex);
    }

    if (bindex - aindex === 1) {
      if (carry === null) {
        carry = aindex;
      } else {
        count++;
      }
    }

    if (bindex - aindex > 1) {
      var final = random(aindex + 1, bindex - 1);

      if (carry !== null) {
        result += final < base.length ? toString(carry) + toString(base.length - 1).repeat(count) : toString(carry + 1) + toString(0).repeat(count);
      }

      result += toString(final % base.length);

      break;
    }

    position++;
  }

  return result;
}

function before(x) {
  var result = '';
  var position = 0;

  while (true) {
    var xindex = toNumber(x[position]);

    if (xindex === 0) {
      result += toString(xindex);
    }

    if (xindex === 1) {
      result += toString(0) + toString(base.length - 1);
      break;
    }

    if (xindex > 1) {
      result += toString(xindex - 1);
      break;
    }

    position++;
  }

  return result;
}

function after(x) {
  var result = '';
  var position = 0;

  while (true) {
    var xindex = toNumber(x[position]);

    if (xindex === base.length - 1) {
      result += toString(xindex);
    } else {
      result += toString(xindex + 1);
      break;
    }

    position++;
  }

  return result;
}

/**
 * Utilities
 */

function random(a, b) {
  var start = a;
  var distance = b - a;

  return Math.round(start + distance * Math.random());
}

function toNumber(x) {
  return base.indexOf(x || base[0]);
}

function toString(x) {
  return base[x];
}

function first() {
  return base[0];
}

function last() {
  var count = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : 64;

  return base[base.length - 1].repeat(count);
}

/**
 * Exports
 */

module.exports = { between: between, before: before, after: after, first: first, last: last };