import re
import string

from unidecode import unidecode


INVALID_PASSWORD_MESSAGE = 'Invalid password, password must be at least ' + \
                           '8 characters and contain no whitespace.'
INVALID_USERNAME_CHARACTERS = r'[^a-z0-9_]'
VALID_CHARACTERS = '_' + string.digits + string.lowercase
MIN_LENGTH = 4
MAX_LENGTH = 30


def validate_email(email_address):
  if re.match(r'[^@]+@[^@]+\.[^@]+', email_address):
    return True
  return False


def validate_username(username):
  # Based off the restrictions defined in the Docker Registry API spec
  regex_match = (re.search(INVALID_USERNAME_CHARACTERS, username) is None)
  if not regex_match:
    return (False, 'Username must match expression [a-z0-9_]+')

  length_match = (len(username) >= MIN_LENGTH and len(username) <= MAX_LENGTH)
  if not length_match:
    return (False, 'Username must be between %s and %s characters in length' %
            (MIN_LENGTH, MAX_LENGTH))

  return (True, '')


def validate_password(password):
  # No whitespace and minimum length of 8
  if re.search(r'\s', password):
    return False
  return len(password) > 7


def _gen_filler_chars(num_filler_chars):
  if num_filler_chars == 0:
    yield ''
  else:
    for char in VALID_CHARACTERS:
      for suffix in _gen_filler_chars(num_filler_chars - 1):
        yield char + suffix


def generate_valid_usernames(input_username):
  normalized = unidecode(input_username).strip().lower()
  prefix = re.sub(INVALID_USERNAME_CHARACTERS, '_', normalized)[:30]

  num_filler_chars = max(0, MIN_LENGTH - len(prefix))

  while num_filler_chars + len(prefix) <= MAX_LENGTH:
    for suffix in _gen_filler_chars(num_filler_chars):
      yield prefix + suffix
    num_filler_chars += 1