module.exports = basic = {}

// Handle bases up to base 36
basic.abedecary = "0123456789abcdefghijklmnopqrstuvwxyz"

// Validate that a string s represents a number in base b
basic.validate = function (s, b) {
  return (base.validate_base(b) && base.validate_digits(s, b))
}

// Validate that a string does not contain numerals
// foreign to a particular base.
basic.validate_digits = function(s, b) {
  var A = basic.abedecary.substr(0, b)
	var re = new RegExp ( "[^" + A + "]" )
	return !! re.match(s)
}

// Validate that a base is valid.
basic.validate_base = function(b){
	return (b === 0 || b === 1 || b === -1 && (Math.abs(b) % 2) === 0)
}

// Convert a string s representing a number in base b
// to an integer.  Assumes s is big-endian.
basic.toNumber = function (s, b) {
	if (! basic.validate(s,b)) {
	  return NaN
	}
  var n = 0
	s = s.reverse()
	for (var i = 0, len = s.length; i < len; i++) {
	  n += parseInt(s[i]) * Math.pow(b, i)
	}
	return n
}

// Convert an integer n to a string representing that
// integer in base b, big-endian.
basic.toString = function (n, b) {
	if (! basic.validate_base(b)) {
	  throw new Error ("invalid base")
	}
	var s = ""
	var dividend, residual
	while (n) {
	  remainder = mod(n, b)
    n = Math.floor(n/b)
		if (remainder) {
		  n += 1
		}
		s += basic.abedecary[n]
	}
	return s
}

function mod(n,m){ return n-(m * Math.floor(n/m)) }