import base64
import string
import json

from random import SystemRandom

import bcrypt
import resumablehashlib

from peewee import TextField, CharField, SmallIntegerField
from data.text import prefix_search


def random_string(length=16):
  random = SystemRandom()
  return ''.join([random.choice(string.ascii_uppercase + string.digits)
                  for _ in range(length)])


class _ResumableSHAField(TextField):
  def _create_sha(self):
    raise NotImplementedError

  def db_value(self, value):
    if value is None:
      return None

    sha_state = value.state()

    # One of the fields is a byte string, let's base64 encode it to make sure
    # we can store and fetch it regardless of default collocation.
    sha_state[3] = base64.b64encode(sha_state[3])

    return json.dumps(sha_state)

  def python_value(self, value):
    if value is None:
      return None

    sha_state = json.loads(value)

    # We need to base64 decode the data bytestring.
    sha_state[3] = base64.b64decode(sha_state[3])
    to_resume = self._create_sha()
    to_resume.set_state(sha_state)
    return to_resume


class ResumableSHA256Field(_ResumableSHAField):
  def _create_sha(self):
    return resumablehashlib.sha256()


class ResumableSHA1Field(_ResumableSHAField):
  def _create_sha(self):
    return resumablehashlib.sha1()


class JSONField(TextField):
  def db_value(self, value):
    return json.dumps(value)

  def python_value(self, value):
    if value is None or value == "":
      return {}
    return json.loads(value)


class Base64BinaryField(TextField):
  def db_value(self, value):
    if value is None:
      return None
    return base64.b64encode(value)

  def python_value(self, value):
    if value is None:
      return None
    return base64.b64decode(value)


class DecryptedValue(object):
  """ Wrapper around an already decrypted value to be placed into an encrypted field. """
  def __init__(self, decrypted_value):
    assert decrypted_value is not None
    self.value = decrypted_value

  def decrypt(self):
    return self.value

  def matches(self, unencrypted_value):
    """ Returns whether the value of this field matches the unencrypted_value. """
    return self.decrypt() == unencrypted_value


class LazyEncryptedValue(object):
  """ Wrapper around an encrypted value in an encrypted field. Will decrypt lazily. """
  def __init__(self, encrypted_value, field):
    self.encrypted_value = encrypted_value
    self._field = field

  def decrypt(self):
    """ Decrypts the value. """
    return self._field.model._meta.encrypter.decrypt_value(self.encrypted_value)

  def matches(self, unencrypted_value):
    """ Returns whether the value of this field matches the unencrypted_value. """
    return self.decrypt() == unencrypted_value

  def __eq__(self, _):
    raise Exception('Disallowed operation; use `matches`')

  def __mod__(self, _):
    raise Exception('Disallowed operation; use `matches`')

  def __pow__(self, _):
    raise Exception('Disallowed operation; use `matches`')

  def __contains__(self, _):
    raise Exception('Disallowed operation; use `matches`')

  def contains(self, _):
    raise Exception('Disallowed operation; use `matches`')

  def startswith(self, _):
    raise Exception('Disallowed operation; use `matches`')

  def endswith(self, _):
    raise Exception('Disallowed operation; use `matches`')


def _add_encryption(field_class, requires_length_check=True):
  """ Adds support for encryption and decryption to the given field class. """
  class indexed_class(field_class):
    def __init__(self, default_token_length=None, *args, **kwargs):
      def _generate_default():
        return DecryptedValue(random_string(default_token_length))

      if default_token_length is not None:
        kwargs['default'] = _generate_default

      field_class.__init__(self, *args, **kwargs)
      assert not self.index

    def db_value(self, value):
      if value is None:
        return None

      if isinstance(value, LazyEncryptedValue):
        return value.encrypted_value

      if isinstance(value, DecryptedValue):
        value = value.value

      meta = self.model._meta
      return meta.encrypter.encrypt_value(value, self.max_length if requires_length_check else None)

    def python_value(self, value):
      if value is None:
        return None

      return LazyEncryptedValue(value, self)

    def __eq__(self, _):
      raise Exception('Disallowed operation; use `matches`')

    def __mod__(self, _):
      raise Exception('Disallowed operation; use `matches`')

    def __pow__(self, _):
      raise Exception('Disallowed operation; use `matches`')

    def __contains__(self, _):
      raise Exception('Disallowed operation; use `matches`')

    def contains(self, _):
      raise Exception('Disallowed operation; use `matches`')

    def startswith(self, _):
      raise Exception('Disallowed operation; use `matches`')

    def endswith(self, _):
      raise Exception('Disallowed operation; use `matches`')

  return indexed_class


EncryptedCharField = _add_encryption(CharField)
EncryptedTextField = _add_encryption(TextField, requires_length_check=False)


class EnumField(SmallIntegerField):
  def __init__(self, enum_type, *args, **kwargs):
    kwargs.pop('index', None)

    super(EnumField, self).__init__(index=True, *args, **kwargs)
    self.enum_type = enum_type

  def db_value(self, value):
      """Convert the python value for storage in the database."""
      return int(value.value)

  def python_value(self, value):
      """Convert the database value to a pythonic value."""
      return self.enum_type(value) if value is not None else None

  def clone_base(self, **kwargs):
    return super(EnumField, self).clone_base(
      enum_type=self.enum_type,
      **kwargs)


def _add_fulltext(field_class):
  """ Adds support for full text indexing and lookup to the given field class. """
  class indexed_class(field_class):
    # Marker used by SQLAlchemy translation layer to add the proper index for full text searching.
    __fulltext__ = True

    def __init__(self, match_function, *args, **kwargs):
      field_class.__init__(self, *args, **kwargs)
      self.match_function = match_function

    def match(self, query):
      return self.match_function(self, query)

    def match_prefix(self, query):
      return prefix_search(self, query)

    def __mod__(self, _):
      raise Exception('Unsafe operation: Use `match` or `match_prefix`')

    def __pow__(self, _):
      raise Exception('Unsafe operation: Use `match` or `match_prefix`')

    def __contains__(self, _):
      raise Exception('Unsafe operation: Use `match` or `match_prefix`')

    def contains(self, _):
      raise Exception('Unsafe operation: Use `match` or `match_prefix`')

    def startswith(self, _):
      raise Exception('Unsafe operation: Use `match` or `match_prefix`')

    def endswith(self, _):
      raise Exception('Unsafe operation: Use `match` or `match_prefix`')

  return indexed_class


FullIndexedCharField = _add_fulltext(CharField)
FullIndexedTextField = _add_fulltext(TextField)


class Credential(object):
  """ Credential represents a hashed credential. """
  def __init__(self, hashed):
    self.hashed = hashed

  def matches(self, value):
    """ Returns true if this credential matches the unhashed value given. """
    return bcrypt.hashpw(value.encode('utf-8'), self.hashed) == self.hashed

  @classmethod
  def from_string(cls, string_value):
    """ Returns a Credential object from an unhashed string value. """
    return Credential(bcrypt.hashpw(string_value.encode('utf-8'), bcrypt.gensalt()))

  @classmethod
  def generate(cls, length=20):
    """ Generates a new credential and returns it, along with its unhashed form. """
    token = random_string(length)
    return Credential.from_string(token), token


class CredentialField(CharField):
  """ A character field that stores crytographically hashed credentials that should never be
      available to the user in plaintext after initial creation. This field automatically
      provides verification.
  """
  def __init__(self, *args, **kwargs):
    CharField.__init__(self, *args, **kwargs)
    assert 'default' not in kwargs
    assert not self.index

  def db_value(self, value):
    if value is None:
      return None

    if isinstance(value, basestring):
      raise Exception('A string cannot be given to a CredentialField; please wrap in a Credential')

    return value.hashed

  def python_value(self, value):
    if value is None:
      return None

    return Credential(value)