text: # Electrum - lightweight Bitcoin client
  # Copyright (C) 2012 thomasv@ecdsa.org
  #
  # Permission is hereby granted, free of charge, to any person
  # obtaining a copy of this software and associated documentation files
  # (the "Software"), to deal in the Software without restriction,
  # including without limitation the rights to use, copy, modify, merge,
  # publish, distribute, sublicense, and/or sell copies of the Software,
  # and to permit persons to whom the Software is furnished to do so,
  # subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be
  # included in all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  # EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  # MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  # NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  # BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  # ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  # CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  # SOFTWARE.
  import os
  import threading
  from typing import Optional
  
  from . import util
  from .bitcoin import Hash, hash_encode, int_to_hex, rev_hex
  from . import constants
  from .util import bfh, bh2u
  
  try:
      import scrypt
      getPoWHash = lambda x: scrypt.hash(x, x, N=1024, r=1, p=1, buflen=32)
  except ImportError:
      util.print_msg("Warning: package scrypt not available; synchronization could be very slow")
      from .scrypt import scrypt_1024_1_1_80 as getPoWHash
  
  
  HEADER_SIZE = 80  # bytes
  MAX_TARGET = 0x00000FFFFF000000000000000000000000000000000000000000000000000000
  
  
  class MissingHeader(Exception):
      pass
  
  class InvalidHeader(Exception):
      pass
  
  def serialize_header(header_dict: dict) -> str:
      s = int_to_hex(header_dict['version'], 4) \
          + rev_hex(header_dict['prev_block_hash']) \
          + rev_hex(header_dict['merkle_root']) \
          + int_to_hex(int(header_dict['timestamp']), 4) \
          + int_to_hex(int(header_dict['bits']), 4) \
          + int_to_hex(int(header_dict['nonce']), 4)
      return s
  
  def deserialize_header(s: bytes, height: int) -> dict:
      if not s:
          raise InvalidHeader('Invalid header: {}'.format(s))
      if len(s) != HEADER_SIZE:
          raise InvalidHeader('Invalid header length: {}'.format(len(s)))
      hex_to_int = lambda s: int('0x' + bh2u(s[::-1]), 16)
      h = {}
      h['version'] = hex_to_int(s[0:4])
      h['prev_block_hash'] = hash_encode(s[4:36])
      h['merkle_root'] = hash_encode(s[36:68])
      h['timestamp'] = hex_to_int(s[68:72])
      h['bits'] = hex_to_int(s[72:76])
      h['nonce'] = hex_to_int(s[76:80])
      h['block_height'] = height
      return h
  
  def hash_header(header: dict) -> str:
      if header is None:
          return '0' * 64
      if header.get('prev_block_hash') is None:
          header['prev_block_hash'] = '00'*32
      return hash_encode(Hash(bfh(serialize_header(header))))
  
  def pow_hash_header(header):
      return hash_encode(getPoWHash(bfh(serialize_header(header))))
  
  
  blockchains = {}
  blockchains_lock = threading.Lock()
  
  
  def read_blockchains(config):
      blockchains[0] = Blockchain(config, 0, None)
      fdir = os.path.join(util.get_headers_dir(config), 'forks')
      util.make_dir(fdir)
      l = filter(lambda x: x.startswith('fork_'), os.listdir(fdir))
      l = sorted(l, key = lambda x: int(x.split('_')[1]))
      for filename in l:
          forkpoint = int(filename.split('_')[2])
          parent_id = int(filename.split('_')[1])
          b = Blockchain(config, forkpoint, parent_id)
          h = b.read_header(b.forkpoint)
          if b.parent().can_connect(h, check_height=False):
              blockchains[b.forkpoint] = b
          else:
              util.print_error("cannot connect", filename)
      return blockchains
  
  
  class Blockchain(util.PrintError):
      """
      Manages blockchain headers and their verification
      """
  
      def __init__(self, config, forkpoint: int, parent_id: int):
          self.config = config
          self.forkpoint = forkpoint
          self.checkpoints = constants.net.CHECKPOINTS
          self.parent_id = parent_id
          assert parent_id != forkpoint
          self.lock = threading.RLock()
          with self.lock:
              self.update_size()
  
      def with_lock(func):
          def func_wrapper(self, *args, **kwargs):
              with self.lock:
                  return func(self, *args, **kwargs)
          return func_wrapper
  
      def parent(self) -> 'Blockchain':
          return blockchains[self.parent_id]
  
      def get_max_child(self) -> Optional[int]:
          with blockchains_lock: chains = list(blockchains.values())
          children = list(filter(lambda y: y.parent_id==self.forkpoint, chains))
          return max([x.forkpoint for x in children]) if children else None
  
      def get_forkpoint(self) -> int:
          mc = self.get_max_child()
          return mc if mc is not None else self.forkpoint
  
      def get_branch_size(self) -> int:
          return self.height() - self.get_forkpoint() + 1
  
      def get_name(self) -> str:
          return self.get_hash(self.get_forkpoint()).lstrip('00')[0:10]
  
      def check_header(self, header: dict) -> bool:
          header_hash = hash_header(header)
          height = header.get('block_height')
          try:
              return header_hash == self.get_hash(height)
          except MissingHeader:
              return False
  
      def fork(parent, header: dict) -> 'Blockchain':
          forkpoint = header.get('block_height')
          self = Blockchain(parent.config, forkpoint, parent.forkpoint)
          open(self.path(), 'w+').close()
          self.save_header(header)
          return self
  
      def height(self) -> int:
          return self.forkpoint + self.size() - 1
  
      def size(self) -> int:
          with self.lock:
              return self._size
  
      def update_size(self) -> None:
          p = self.path()
          self._size = os.path.getsize(p)//HEADER_SIZE if os.path.exists(p) else 0
  
      def verify_header(self, header: dict, prev_hash: str, target: int, expected_header_hash: str=None) -> None:
          _hash = hash_header(header)
          _powhash = pow_hash_header(header)
          if expected_header_hash and expected_header_hash != _hash:
              raise Exception("hash mismatches with expected: {} vs {}".format(expected_header_hash, _hash))
          if prev_hash != header.get('prev_block_hash'):
              raise Exception("prev hash mismatch: %s vs %s" % (prev_hash, header.get('prev_block_hash')))
          if constants.net.TESTNET:
              return
          bits = self.target_to_bits(target)
          if bits != header.get('bits'):
              raise Exception("bits mismatch: %s vs %s" % (bits, header.get('bits')))
          if int('0x' + _powhash, 16) > target:
              raise Exception("insufficient proof of work: %s vs target %s" % (int('0x' + _powhash, 16), target))
  
      def verify_chunk(self, index: int, data: bytes) -> None:
          num = len(data) // HEADER_SIZE
          start_height = index * 2016
          prev_hash = self.get_hash(start_height - 1)
          target = self.get_target(index-1)
          for i in range(num):
              height = start_height + i
              try:
                  expected_header_hash = self.get_hash(height)
              except MissingHeader:
                  expected_header_hash = None
              raw_header = data[i*HEADER_SIZE : (i+1)*HEADER_SIZE]
              header = deserialize_header(raw_header, index*2016 + i)
              self.verify_header(header, prev_hash, target, expected_header_hash)
              prev_hash = hash_header(header)
  
      def path(self):
          d = util.get_headers_dir(self.config)
          if self.parent_id is None:
              filename = 'blockchain_headers'
          else:
              basename = 'fork_%d_%d' % (self.parent_id, self.forkpoint)
              filename = os.path.join('forks', basename)
          return os.path.join(d, filename)
  
      @with_lock
      def save_chunk(self, index: int, chunk: bytes):
          chunk_within_checkpoint_region = index < len(self.checkpoints)
          # chunks in checkpoint region are the responsibility of the 'main chain'
          if chunk_within_checkpoint_region and self.parent_id is not None:
              main_chain = blockchains[0]
              main_chain.save_chunk(index, chunk)
              return
  
          delta_height = (index * 2016 - self.forkpoint)
          delta_bytes = delta_height * HEADER_SIZE
          # if this chunk contains our forkpoint, only save the part after forkpoint
          # (the part before is the responsibility of the parent)
          if delta_bytes < 0:
              chunk = chunk[-delta_bytes:]
              delta_bytes = 0
          truncate = not chunk_within_checkpoint_region
          self.write(chunk, delta_bytes, truncate)
          self.swap_with_parent()
  
      @with_lock
      def swap_with_parent(self) -> None:
          if self.parent_id is None:
              return
          parent_branch_size = self.parent().height() - self.forkpoint + 1
          if parent_branch_size >= self.size():
              return
          self.print_error("swap", self.forkpoint, self.parent_id)
          parent_id = self.parent_id
          forkpoint = self.forkpoint
          parent = self.parent()
          self.assert_headers_file_available(self.path())
          with open(self.path(), 'rb') as f:
              my_data = f.read()
          self.assert_headers_file_available(parent.path())
          with open(parent.path(), 'rb') as f:
              f.seek((forkpoint - parent.forkpoint)*HEADER_SIZE)
              parent_data = f.read(parent_branch_size*HEADER_SIZE)
          self.write(parent_data, 0)
          parent.write(my_data, (forkpoint - parent.forkpoint)*HEADER_SIZE)
          # store file path
          with blockchains_lock: chains = list(blockchains.values())
          for b in chains:
              b.old_path = b.path()
          # swap parameters
          self.parent_id = parent.parent_id; parent.parent_id = parent_id
          self.forkpoint = parent.forkpoint; parent.forkpoint = forkpoint
          self._size = parent._size; parent._size = parent_branch_size
          # move files
          for b in chains:
              if b in [self, parent]: continue
              if b.old_path != b.path():
                  self.print_error("renaming", b.old_path, b.path())
                  os.rename(b.old_path, b.path())
          # update pointers
          with blockchains_lock:
              blockchains[self.forkpoint] = self
              blockchains[parent.forkpoint] = parent
  
      def assert_headers_file_available(self, path):
          if os.path.exists(path):
              return
          elif not os.path.exists(util.get_headers_dir(self.config)):
              raise FileNotFoundError('Electrum headers_dir does not exist. Was it deleted while running?')
          else:
              raise FileNotFoundError('Cannot find headers file but headers_dir is there. Should be at {}'.format(path))
  
      def write(self, data: bytes, offset: int, truncate: bool=True) -> None:
          filename = self.path()
          with self.lock:
              self.assert_headers_file_available(filename)
              with open(filename, 'rb+') as f:
                  if truncate and offset != self._size * HEADER_SIZE:
                      f.seek(offset)
                      f.truncate()
                  f.seek(offset)
                  f.write(data)
                  f.flush()
                  os.fsync(f.fileno())
              self.update_size()
  
      @with_lock
      def save_header(self, header: dict) -> None:
          delta = header.get('block_height') - self.forkpoint
          data = bfh(serialize_header(header))
          # headers are only _appended_ to the end:
          assert delta == self.size()
          assert len(data) == HEADER_SIZE
          self.write(data, delta*HEADER_SIZE)
          self.swap_with_parent()
  
      def read_header(self, height: int) -> Optional[dict]:
          assert self.parent_id != self.forkpoint
          if height < 0:
              return
          if height < self.forkpoint:
              return self.parent().read_header(height)
          if height > self.height():
              return
          delta = height - self.forkpoint
          name = self.path()
          self.assert_headers_file_available(name)
          with open(name, 'rb') as f:
              f.seek(delta * HEADER_SIZE)
              h = f.read(HEADER_SIZE)
              if len(h) < HEADER_SIZE:
                  raise Exception('Expected to read a full header. This was only {} bytes'.format(len(h)))
          if h == bytes([0])*HEADER_SIZE:
              return None
          return deserialize_header(h, height)
  
      def get_hash(self, height: int) -> str:
          def is_height_checkpoint():
              within_cp_range = height <= constants.net.max_checkpoint()
              at_chunk_boundary = (height+1) % 2016 == 0
              return within_cp_range and at_chunk_boundary
  
          if height == -1:
              return '0000000000000000000000000000000000000000000000000000000000000000'
          elif height == 0:
              return constants.net.GENESIS
          elif is_height_checkpoint():
              index = height // 2016
              h, t, _ = self.checkpoints[index]
              return h
          else:
              header = self.read_header(height)
              if header is None:
                  raise MissingHeader(height)
              return hash_header(header)
  
      def get_timestamp(self, height):
          if height < len(self.checkpoints) * 2016 and (height+1) % 2016 == 0:
              index = height // 2016
              _, _, ts = self.checkpoints[index]
              return ts
          return self.read_header(height).get('timestamp')
  
      def get_target(self, index: int) -> int:
          # compute target from chunk x, used in chunk x+1
          if constants.net.TESTNET:
              return 0
          if index == -1:
              return 0x00000FFFF0000000000000000000000000000000000000000000000000000000
          if index < len(self.checkpoints):
              h, t, _ = self.checkpoints[index]
              return t
          # new target
          # Bitcored: go back the full period unless it's the first retarget
          first_timestamp = self.get_timestamp(index * 2016 - 1 if index > 0 else 0)
          last = self.read_header(index * 2016 + 2015)
          if not first_timestamp or not last:
              raise MissingHeader()
          bits = last.get('bits')
          target = self.bits_to_target(bits)
          nActualTimespan = last.get('timestamp') - first_timestamp
          nTargetTimespan = 84 * 60 * 60
          nActualTimespan = max(nActualTimespan, nTargetTimespan // 4)
          nActualTimespan = min(nActualTimespan, nTargetTimespan * 4)
          new_target = min(MAX_TARGET, (target * nActualTimespan) // nTargetTimespan)
          return new_target
  
      def bits_to_target(self, bits: int) -> int:
          bitsN = (bits >> 24) & 0xff
          if not (bitsN >= 0x03 and bitsN <= 0x1e):
              raise Exception("First part of bits should be in [0x03, 0x1e]")
          bitsBase = bits & 0xffffff
          if not (bitsBase >= 0x8000 and bitsBase <= 0x7fffff):
              raise Exception("Second part of bits should be in [0x8000, 0x7fffff]")
          return bitsBase << (8 * (bitsN-3))
  
      def target_to_bits(self, target: int) -> int:
          c = ("%064x" % target)[2:]
          while c[:2] == '00' and len(c) > 6:
              c = c[2:]
          bitsN, bitsBase = len(c) // 2, int('0x' + c[:6], 16)
          if bitsBase >= 0x800000:
              bitsN += 1
              bitsBase >>= 8
          return bitsN << 24 | bitsBase
  
      def can_connect(self, header: dict, check_height: bool=True) -> bool:
          if header is None:
              return False
          height = header['block_height']
          if check_height and self.height() != height - 1:
              #self.print_error("cannot connect at height", height)
              return False
          if height == 0:
              return hash_header(header) == constants.net.GENESIS
          try:
              prev_hash = self.get_hash(height - 1)
          except:
              return False
          if prev_hash != header.get('prev_block_hash'):
              return False
          try:
              target = self.get_target(height // 2016 - 1)
          except MissingHeader:
              return False
          try:
              self.verify_header(header, prev_hash, target)
          except BaseException as e:
              return False
          return True
  
      def connect_chunk(self, idx: int, hexdata: str) -> bool:
          try:
              data = bfh(hexdata)
              self.verify_chunk(idx, data)
              #self.print_error("validated chunk %d" % idx)
              self.save_chunk(idx, data)
              return True
          except BaseException as e:
              self.print_error('verify_chunk %d failed'%idx, str(e))
              return False
  
      def get_checkpoints(self):
          # for each chunk, store the hash of the last block and the target after the chunk
          cp = []
          n = self.height() // 2016
          for index in range(n):
              h = self.get_hash((index+1) * 2016 -1)
              target = self.get_target(index)
              # Bitcored: also store the timestamp of the last block
              tstamp = self.get_timestamp((index+1) * 2016 - 1)
              cp.append((h, target, tstamp))
          return cp
  
  
  def check_header(header: dict) -> Optional[Blockchain]:
      if type(header) is not dict:
          return None
      with blockchains_lock: chains = list(blockchains.values())
      for b in chains:
          if b.check_header(header):
              return b
      return None
  
  
  def can_connect(header: dict) -> Optional[Blockchain]:
      with blockchains_lock: chains = list(blockchains.values())
      for b in chains:
          if b.can_connect(header):
              return b
      return None
  