url hash

generateCode.coffee

getAlgorithms = -> ['md5', 'sha1', 'sha256', 'sha512']

generateCode = (url, algorithms, digits, callback)->
  #increase code digits if all codes are registered
  if algorithms.length is 0
    algorithms = getAlgorithms()
    digits += 1

  algorithm = algorithms.shift()

  code = hashUrl(url, digits, algorithm)

  redis.get "url:#{code}", (err, reply)->
    if not reply or reply == url
      redis.set "url:#{code}", url, (err, reply)->
        callback(null, code)
    else generateCode(url, algorithms, digits, callback)

hashUrl.coffee

exports.hashUrl = hashUrl = (url, digits = 5, algorithm = 'md5')->
  symbols = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890'
  length = symbols.length
  code = ""

  hash = crypto.createHash(algorithm)
    .update(url)
    .digest('hex')

  hash_number = parseInt(hash, 16) % Math.pow(length, digits + 1)

  while hash_number >= length
    n = hash_number % length
    code += symbols[n]
    hash_number = parseInt(hash_number / length)

  code