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 . import util
  from . import bitcoin
  from . import constants
  from .bitcoin import *
  
  import lyra2re_hash
  import lyra2re2_hash
  import vtc_scrypt_new
  
  MAX_TARGET = 0x00000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
  
  def serialize_header(res):
      s = int_to_hex(res.get('version'), 4) \
          + rev_hex(res.get('prev_block_hash')) \
          + rev_hex(res.get('merkle_root')) \
          + int_to_hex(int(res.get('timestamp')), 4) \
          + int_to_hex(int(res.get('bits')), 4) \
          + int_to_hex(int(res.get('nonce')), 4)
      return s
  
  def deserialize_header(s, height):
      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):
      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):
      height = header.get('block_height')
      header_bytes = bfh(serialize_header(header))
      if height >= 347000:
          return hash_encode(lyra2re2_hash.getPoWHash(header_bytes))
      elif height >= 208301:
          return hash_encode(lyra2re_hash.getPoWHash(header_bytes))
      else:
          return hash_encode(vtc_scrypt_new.getPoWHash(header_bytes))
  
  blockchains = {}
  
  def read_blockchains(config):
      blockchains[0] = Blockchain(config, 0, None)
      fdir = os.path.join(util.get_headers_dir(config), 'forks')
      if not os.path.exists(fdir):
          os.mkdir(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:
          checkpoint = int(filename.split('_')[2])
          parent_id = int(filename.split('_')[1])
          b = Blockchain(config, checkpoint, parent_id)
          h = b.read_header(b.checkpoint)
          if b.parent().can_connect(h, check_height=False):
              blockchains[b.checkpoint] = b
          else:
              util.print_error("cannot connect", filename)
      return blockchains
  
  def check_header(header):
      if type(header) is not dict:
          return False
      for b in blockchains.values():
          if b.check_header(header):
              return b
      return False
  
  def can_connect(header):
      for b in blockchains.values():
          if b.can_connect(header):
              return b
      return False
  
  
  class Blockchain(util.PrintError):
      """
      Manages blockchain headers and their verification
      """
  
      def __init__(self, config, checkpoint, parent_id):
          self.config = config
          self.catch_up = None # interface catching up
          self.checkpoint = checkpoint
          self.checkpoints = constants.net.CHECKPOINTS
          self.parent_id = parent_id
          self.lock = threading.Lock()
          with self.lock:
              self.update_size()
  
      def parent(self):
          return blockchains[self.parent_id]
  
      def get_max_child(self):
          children = list(filter(lambda y: y.parent_id==self.checkpoint, blockchains.values()))
          return max([x.checkpoint for x in children]) if children else None
  
      def get_checkpoint(self):
          mc = self.get_max_child()
          return mc if mc is not None else self.checkpoint
  
      def get_branch_size(self):
          return self.height() - self.get_checkpoint() + 1
  
      def get_name(self):
          return self.get_hash(self.get_checkpoint()).lstrip('00')[0:10]
  
      def check_header(self, header):
          header_hash = hash_header(header)
          height = header.get('block_height')
          return header_hash == self.get_hash(height)
  
      def fork(parent, header):
          checkpoint = header.get('block_height')
          self = Blockchain(parent.config, checkpoint, parent.checkpoint)
          open(self.path(), 'w+').close()
          self.save_header(header)
          return self
  
      def height(self):
          return self.checkpoint + self.size() - 1
  
      def size(self):
          with self.lock:
              return self._size
  
      def update_size(self):
          p = self.path()
          self._size = os.path.getsize(p)//80 if os.path.exists(p) else 0
  
      def verify_header(self, header, prev_hash, bits, target, check_bits_target=True):
          _hash = hash_header(header)
          if prev_hash != header.get('prev_block_hash'):
              raise BaseException("prev hash mismatch: %s vs %s" % (prev_hash, header.get('prev_block_hash')))
          if constants.net.TESTNET:
              return
          if check_bits_target:
              if bits != header.get('bits'):
                  raise BaseException("bits mismatch: %s vs %s" % (bits, header.get('bits')))
              
              _powhash = pow_hash_header(header)
              if int('0x' + _powhash, 16) > target:
                  raise BaseException("insufficient proof of work: %s vs target %s" % (int('0x' + _powhash, 16), target))
  
      def should_check_bits_target(self, height):
          index = height // 2016
          return (index > len(self.checkpoints) + 1) or \
              (index < len(self.checkpoints) and height % 2016 == 0)
      
      def verify_chunk(self, index, data):
          num = len(data) // 80
          prev_hash = self.get_hash(index * 2016 - 1)
          headers = {}
          for i in range(num):
              raw_header = data[i*80:(i+1) * 80]
              header = deserialize_header(raw_header, index*2016 + i)
              headers[header.get('block_height')] = header
  
              bits, target = None, None
              check_bits_target = self.should_check_bits_target(index * 2016 + i)
              if(check_bits_target):
                  bits, target = self.get_target(index * 2016 + i, headers)
  
              self.verify_header(header, prev_hash, bits, target, check_bits_target)
              prev_hash = hash_header(header)
  
      def path(self):
          d = util.get_headers_dir(self.config)
          filename = 'blockchain_headers' if self.parent_id is None else os.path.join('forks', 'fork_%d_%d'%(self.parent_id, self.checkpoint))
          return os.path.join(d, filename)
  
      def save_chunk(self, index, chunk):
          filename = self.path()
          d = (index * 2016 - self.checkpoint) * 80
          if d < 0:
              chunk = chunk[-d:]
              d = 0
          truncate = index >= len(self.checkpoints)
          self.write(chunk, d, truncate)
          self.swap_with_parent()
  
      def swap_with_parent(self):
          if self.parent_id is None:
              return
          parent_branch_size = self.parent().height() - self.checkpoint + 1
          if parent_branch_size >= self.size():
              return
          self.print_error("swap", self.checkpoint, self.parent_id)
          parent_id = self.parent_id
          checkpoint = self.checkpoint
          parent = self.parent()
          with open(self.path(), 'rb') as f:
              my_data = f.read()
          with open(parent.path(), 'rb') as f:
              f.seek((checkpoint - parent.checkpoint)*80)
              parent_data = f.read(parent_branch_size*80)
          self.write(parent_data, 0)
          parent.write(my_data, (checkpoint - parent.checkpoint)*80)
          # store file path
          for b in blockchains.values():
              b.old_path = b.path()
          # swap parameters
          self.parent_id = parent.parent_id; parent.parent_id = parent_id
          self.checkpoint = parent.checkpoint; parent.checkpoint = checkpoint
          self._size = parent._size; parent._size = parent_branch_size
          # move files
          for b in blockchains.values():
              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
          blockchains[self.checkpoint] = self
          blockchains[parent.checkpoint] = parent
  
      def write(self, data, offset, truncate=True):
          filename = self.path()
          with self.lock:
              with open(filename, 'rb+') as f:
                  if truncate and offset != self._size*80:
                      f.seek(offset)
                      f.truncate()
                  f.seek(offset)
                  f.write(data)
                  f.flush()
                  os.fsync(f.fileno())
              self.update_size()
  
      def save_header(self, header):
          delta = header.get('block_height') - self.checkpoint
          data = bfh(serialize_header(header))
          assert delta == self.size()
          assert len(data) == 80
          self.write(data, delta*80)
          self.swap_with_parent()
  
      def read_header(self, height):
          assert self.parent_id != self.checkpoint
          if height < 0:
              return
          if height < self.checkpoint:
              return self.parent().read_header(height)
          if height > self.height():
              return
          delta = height - self.checkpoint
          name = self.path()
          if os.path.exists(name):
              with open(name, 'rb') as f:
                  f.seek(delta * 80)
                  h = f.read(80)
          elif not os.path.exists(util.get_headers_dir(self.config)):
              raise Exception('Electrum datadir does not exist. Was it deleted while running?')
          else:
              raise Exception('Cannot find headers file but datadir is there. Should be at {}'.format(name))
          if h == bytes([0])*80:
              return None
          return deserialize_header(h, height)
  
      def get_hash(self, height):
          if height == -1:
              return '0000000000000000000000000000000000000000000000000000000000000000'
          elif height == 0:
              return constants.net.GENESIS
          elif height < len(self.checkpoints) * 2016:
              assert (height+1) % 2016 == 0, height
              index = height // 2016
              h, _, _, _ = self.checkpoints[index]
              return h
          else:
              return hash_header(self.read_header(height))
  
      def convbits(self, new_target):
          c = ("%064x" % int(new_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
          new_bits = bitsN << 24 | bitsBase
          return new_bits
          
      def convbignum(self, bits):
          bitsN = (bits >> 24) & 0xff
          if not (bitsN >= 0x03 and bitsN <= 0x1e):
              raise BaseException("First part of bits should be in [0x03, 0x1e]")
          bitsBase = bits & 0xffffff
          if not (bitsBase >= 0x8000 and bitsBase <= 0x7fffff):
              raise BaseException("Second part of bits should be in [0x8000, 0x7fffff]")
          target = bitsBase << (8 * (bitsN-3))
          return target
  
      def KimotoGravityWell(self, height, chain={}):
          BlocksTargetSpacing = 2.5 * 60  # 2.5 minutes
          TimeDaySeconds = 60 * 60 * 24
          PastSecondsMin = TimeDaySeconds * 0.25
          PastSecondsMax = TimeDaySeconds * 7
          PastBlocksMin = PastSecondsMin / BlocksTargetSpacing
          PastBlocksMax = PastSecondsMax / BlocksTargetSpacing
  
          BlockReadingIndex = height - 1
          BlockLastSolvedIndex = height - 1
          TargetBlocksSpacingSeconds = BlocksTargetSpacing
          PastRateAdjustmentRatio = 1.0
          bnProofOfWorkLimit = 0x00000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
  
          if (BlockLastSolvedIndex <= 0 or BlockLastSolvedIndex < PastSecondsMin):
              new_target = bnProofOfWorkLimit
              new_bits = self.convbits(new_target)
              return new_bits, new_target
  
          last = chain.get(BlockLastSolvedIndex)
          if last == None:
              last = self.read_header(BlockLastSolvedIndex)
  
          for i in range(1, int(PastBlocksMax)+1):
              PastBlocksMass = i
  
              reading = chain.get(BlockReadingIndex)
              if reading == None:
                  reading = self.read_header(BlockReadingIndex)
                  chain[BlockReadingIndex] = reading
  
              if (reading == None or last == None):
                  raise BaseException("Could not find previous blocks when calculating difficulty reading: " + str(BlockReadingIndex) + ", last: " + str(BlockLastSolvedIndex) + ", height: " + str(height))
  
              if (i == 1):
                  PastDifficultyAverage = self.convbignum(reading.get('bits'))
              else:
                  PastDifficultyAverage = float((self.convbignum(reading.get('bits')) - PastDifficultyAveragePrev) / float(i)) + PastDifficultyAveragePrev
  
              PastDifficultyAveragePrev = PastDifficultyAverage
  
              PastRateActualSeconds = last.get('timestamp') - reading.get('timestamp')
              PastRateTargetSeconds = TargetBlocksSpacingSeconds * PastBlocksMass
              PastRateAdjustmentRatio = 1.0
              if (PastRateActualSeconds < 0):
                  PastRateActualSeconds = 0.0
  
              if (PastRateActualSeconds != 0 and PastRateTargetSeconds != 0):
                  PastRateAdjustmentRatio = float(PastRateTargetSeconds) / float(PastRateActualSeconds)
  
              EventHorizonDeviation = 1 + (0.7084 * pow(float(PastBlocksMass)/float(144), -1.228))
              EventHorizonDeviationFast = EventHorizonDeviation
              EventHorizonDeviationSlow = float(1) / float(EventHorizonDeviation)
  
              if (PastBlocksMass >= PastBlocksMin):
  
                  if ((PastRateAdjustmentRatio <= EventHorizonDeviationSlow) or (PastRateAdjustmentRatio >= EventHorizonDeviationFast)):
                      break
  
                  if (BlockReadingIndex < 1):
                      break
  
              BlockReadingIndex = BlockReadingIndex - 1
  
          bnNew = PastDifficultyAverage
          if (PastRateActualSeconds != 0 and PastRateTargetSeconds != 0):
              bnNew *= float(PastRateActualSeconds)
              bnNew /= float(PastRateTargetSeconds)
  
          if (bnNew > bnProofOfWorkLimit):
              bnNew = bnProofOfWorkLimit
  
          # new target
          new_target = bnNew
          new_bits = self.convbits(new_target)
  
          #print_msg("bits", new_bits , "(", hex(new_bits),")")
          #print_msg ("PastRateAdjustmentRatio=",PastRateAdjustmentRatio,"EventHorizonDeviationSlow",EventHorizonDeviationSlow,"PastSecondsMin=",PastSecondsMin,"PastSecondsMax=",PastSecondsMax,"PastBlocksMin=",PastBlocksMin,"PastBlocksMax=",PastBlocksMax)
          return new_bits, new_target
  
      def get_target(self, height, chain={}):
          if constants.net.TESTNET:
              return 0, 0
          if height <= 0 or height == 208301:
              return 0x1e0ffff0, 0x00000FFFF0000000000000000000000000000000000000000000000000000000
          if height == 468741:
              bits = 469820683
              bitsBase = bits & 0xffffff
              bitsN = (bits >> 24) & 0xff
              target = bitsBase << (8 * (bitsN - 3))
              return bits, target 
          index = height // 2016
          if index < len(self.checkpoints) and (height % 2016 == 0):
              _, t, b, _ = self.checkpoints[index]
              return b, t
          if height < 26754:
              # Litecoin: go back the full period unless it's the first retarget
              first = self.read_header((height - 2016 - 1 if height > 2016 else 0))
              last = self.read_header(height - 1)
              if last is None:
                  last = chain.get(height - 1)
              assert last is not None
              # bits to target
              bits = last.get('bits')
              bitsN = (bits >> 24) & 0xff
              if not (bitsN >= 0x03 and bitsN <= 0x1e):
                  raise BaseException("First part of bits should be in [0x03, 0x1e]")
              bitsBase = bits & 0xffffff
              if not (bitsBase >= 0x8000 and bitsBase <= 0x7fffff):
                  raise BaseException("Second part of bits should be in [0x8000, 0x7fffff]")
              target = bitsBase << (8 * (bitsN-3))
              if height % 2016 != 0:
                  return bits, target
              # new target
              nActualTimespan = last.get('timestamp') - first.get('timestamp')
              nTargetTimespan = 84 * 60 * 60
              nActualTimespan = max(nActualTimespan, nTargetTimespan // 4)
              nActualTimespan = min(nActualTimespan, nTargetTimespan * 4)
              new_target = min(MAX_TARGET, (target*nActualTimespan) // nTargetTimespan)
              # convert new target to bits
              c = ("%064x" % int(new_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
              new_bits = bitsN << 24 | bitsBase
              return new_bits, bitsBase << (8 * (bitsN-3))                
          else:
              return self.KimotoGravityWell(height, chain)
  
      def can_connect(self, header, check_height=True):
          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
          bits, target = None, None
          check_bits_target = self.should_check_bits_target(height)
          if(check_bits_target):
              bits, target = self.get_target(height)
          try:
              self.verify_header(header, prev_hash, bits, target, check_bits_target)
          except BaseException as e:
              return False
          return True
  
      def connect_chunk(self, idx, hexdata):
          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)
              bits, target = self.get_target(index * 2016)
              cp.append((h, target, bits, index))
          return cp
  