import hashlib
import time

from binascii import hexlify
from cachetools import lru_cache

import bencode
import jwt
import resumablehashlib

from app import app, instance_keys


ANNOUNCE_URL = app.config['BITTORRENT_ANNOUNCE_URL']
FILENAME_PEPPER = app.config['BITTORRENT_FILENAME_PEPPER']
REGISTRY_TITLE = app.config['REGISTRY_TITLE']


@lru_cache(maxsize=1)
def _load_private_key(private_key_file_path):
  with open(private_key_file_path) as private_key_file:
    return private_key_file.read()


def jwt_from_infodict(infodict):
  """ Returns an encoded JWT for the given BitTorrent info dict, signed by the local instance's
      private key.
  """
  digest = hashlib.sha1()
  digest.update(bencode.bencode(infodict))
  return jwt_from_infohash(digest.digest())


def jwt_from_infohash(infohash_digest):
  """ Returns an encoded JWT for the given BitTorrent infohash, signed by the local instance's
      private key.
  """
  token_data = {
    'iss': instance_keys.service_name,
    'aud': ANNOUNCE_URL,
    'infohash': hexlify(infohash_digest),
  }
  return jwt.encode(token_data, instance_keys.local_private_key, algorithm='RS256',
                    headers={'kid': instance_keys.local_key_id})


def make_torrent(name, webseed, length, piece_length, pieces):
  info_dict = {
    'name': name,
    'length': length,
    'piece length': piece_length,
    'pieces': pieces,
    'private': 1,
  }

  return bencode.bencode({
    'announce': ANNOUNCE_URL + "?jwt=" + jwt_from_infodict(info_dict),
    'url-list': str(webseed),
    'encoding': 'UTF-8',
    'created by': REGISTRY_TITLE,
    'creation date': int(time.time()),
    'info': info_dict,
  })


def public_torrent_filename(blob_uuid):
  return hashlib.sha256(blob_uuid).hexdigest()


def per_user_torrent_filename(user_uuid, blob_uuid):
  return hashlib.sha256(FILENAME_PEPPER + "||" + blob_uuid + "||" + user_uuid).hexdigest()


class PieceHasher(object):
  """ Utility for computing torrent piece hashes as the data flows through the update
      method of this class. Users should get the final value by calling final_piece_hashes
      since new chunks are allocated lazily.
  """
  def __init__(self, piece_size, starting_offset=0, starting_piece_hash_bytes='',
               hash_fragment_to_resume=None):
    if not isinstance(starting_offset, (int, long)):
      raise TypeError('starting_offset must be an integer')
    elif not isinstance(piece_size, (int, long)):
      raise TypeError('piece_size must be an integer')

    self._current_offset = starting_offset
    self._piece_size = piece_size
    self._piece_hashes = bytearray(starting_piece_hash_bytes)

    if hash_fragment_to_resume is None:
      self._hash_fragment = resumablehashlib.sha1()
    else:
      self._hash_fragment = hash_fragment_to_resume


  def update(self, buf):
    buf_offset = 0
    while buf_offset < len(buf):
      buf_bytes_to_hash = buf[0:self._piece_length_remaining()]
      to_hash_len = len(buf_bytes_to_hash)

      if self._piece_offset() == 0 and to_hash_len > 0 and self._current_offset > 0:
        # We are opening a new piece
        self._piece_hashes.extend(self._hash_fragment.digest())
        self._hash_fragment = resumablehashlib.sha1()

      self._hash_fragment.update(buf_bytes_to_hash)
      self._current_offset += to_hash_len
      buf_offset += to_hash_len

  @property
  def hashed_bytes(self):
    return self._current_offset

  def _piece_length_remaining(self):
    return self._piece_size - (self._current_offset % self._piece_size)

  def _piece_offset(self):
    return self._current_offset % self._piece_size

  @property
  def piece_hashes(self):
    return self._piece_hashes

  @property
  def hash_fragment(self):
    return self._hash_fragment

  def final_piece_hashes(self):
    return self._piece_hashes + self._hash_fragment.digest()