text: #!/usr/bin/env python3
  # Copyright (c) 2015-2017 The Bitcoin Core developers
  # Distributed under the MIT software license, see the accompanying
  # file COPYING or http://www.opensource.org/licenses/mit-license.php.
  """Utilities for manipulating blocks and transactions."""
  
  from .address import (
      key_to_p2sh_p2wpkh,
      key_to_p2wpkh,
      script_to_p2sh_p2wsh,
      script_to_p2wsh,
  )
  from .mininode import *
  from .script import (
      CScript,
      OP_0,
      OP_1,
      OP_CHECKMULTISIG,
      OP_CHECKSIG,
      OP_RETURN,
      OP_TRUE,
      hash160,
  )
  from .util import assert_equal
  
  # Create a block (with regtest difficulty)
  def create_block(hashprev, coinbase, nTime=None):
      block = CBlock()
      if nTime is None:
          import time
          block.nTime = int(time.time()+600)
      else:
          block.nTime = nTime
      block.hashPrevBlock = hashprev
      block.nBits = 0x207fffff # Will break after a difficulty adjustment...
      block.vtx.append(coinbase)
      block.hashMerkleRoot = block.calc_merkle_root()
      block.calc_sha256()
      return block
  
  # From BIP141
  WITNESS_COMMITMENT_HEADER = b"\xaa\x21\xa9\xed"
  
  
  def get_witness_script(witness_root, witness_nonce):
      witness_commitment = uint256_from_str(hash256(ser_uint256(witness_root)+ser_uint256(witness_nonce)))
      output_data = WITNESS_COMMITMENT_HEADER + ser_uint256(witness_commitment)
      return CScript([OP_RETURN, output_data])
  
  
  # According to BIP141, blocks with witness rules active must commit to the
  # hash of all in-block transactions including witness.
  def add_witness_commitment(block, nonce=0):
      # First calculate the merkle root of the block's
      # transactions, with witnesses.
      witness_nonce = nonce
      witness_root = block.calc_witness_merkle_root()
      # witness_nonce should go to coinbase witness.
      block.vtx[0].wit.vtxinwit = [CTxInWitness()]
      block.vtx[0].wit.vtxinwit[0].scriptWitness.stack = [ser_uint256(witness_nonce)]
  
      # witness commitment is the last OP_RETURN output in coinbase
      block.vtx[0].vout.append(CTxOut(0, get_witness_script(witness_root, witness_nonce)))
      block.vtx[0].rehash()
      block.hashMerkleRoot = block.calc_merkle_root()
      block.rehash()
  
  
  def serialize_script_num(value):
      r = bytearray(0)
      if value == 0:
          return r
      neg = value < 0
      absvalue = -value if neg else value
      while (absvalue):
          r.append(int(absvalue & 0xff))
          absvalue >>= 8
      if r[-1] & 0x80:
          r.append(0x80 if neg else 0)
      elif neg:
          r[-1] |= 0x80
      return r
  
  # Create a coinbase transaction, assuming no miner fees.
  # If pubkey is passed in, the coinbase output will be a P2PK output;
  # otherwise an anyone-can-spend output.
  def create_coinbase(height, pubkey = None):
      coinbase = CTransaction()
      coinbase.vin.append(CTxIn(COutPoint(0, 0xffffffff), 
                  ser_string(serialize_script_num(height)), 0xffffffff))
      coinbaseoutput = CTxOut()
      coinbaseoutput.nValue = 1 * COIN
      halvings = int(height/150) # regtest
      coinbaseoutput.nValue >>= halvings
      if (pubkey != None):
          coinbaseoutput.scriptPubKey = CScript([pubkey, OP_CHECKSIG])
      else:
          coinbaseoutput.scriptPubKey = CScript([OP_TRUE])
      coinbase.vout = [ coinbaseoutput ]
      coinbase.calc_sha256()
      return coinbase
  
  # Create a transaction.
  # If the scriptPubKey is not specified, make it anyone-can-spend.
  def create_transaction(prevtx, n, sig, value, scriptPubKey=CScript()):
      tx = CTransaction()
      assert(n < len(prevtx.vout))
      tx.vin.append(CTxIn(COutPoint(prevtx.sha256, n), sig, 0xffffffff))
      tx.vout.append(CTxOut(value, scriptPubKey))
      tx.calc_sha256()
      return tx
  
  def get_legacy_sigopcount_block(block, fAccurate=True):
      count = 0
      for tx in block.vtx:
          count += get_legacy_sigopcount_tx(tx, fAccurate)
      return count
  
  def get_legacy_sigopcount_tx(tx, fAccurate=True):
      count = 0
      for i in tx.vout:
          count += i.scriptPubKey.GetSigOpCount(fAccurate)
      for j in tx.vin:
          # scriptSig might be of type bytes, so convert to CScript for the moment
          count += CScript(j.scriptSig).GetSigOpCount(fAccurate)
      return count
  
  # Create a scriptPubKey corresponding to either a P2WPKH output for the
  # given pubkey, or a P2WSH output of a 1-of-1 multisig for the given
  # pubkey. Returns the hex encoding of the scriptPubKey.
  def witness_script(use_p2wsh, pubkey):
      if (use_p2wsh == False):
          # P2WPKH instead
          pubkeyhash = hash160(hex_str_to_bytes(pubkey))
          pkscript = CScript([OP_0, pubkeyhash])
      else:
          # 1-of-1 multisig
          witness_program = CScript([OP_1, hex_str_to_bytes(pubkey), OP_1, OP_CHECKMULTISIG])
          scripthash = sha256(witness_program)
          pkscript = CScript([OP_0, scripthash])
      return bytes_to_hex_str(pkscript)
  
  # Return a transaction (in hex) that spends the given utxo to a segwit output,
  # optionally wrapping the segwit output using P2SH.
  def create_witness_tx(node, use_p2wsh, utxo, pubkey, encode_p2sh, amount):
      if use_p2wsh:
          program = CScript([OP_1, hex_str_to_bytes(pubkey), OP_1, OP_CHECKMULTISIG])
          addr = script_to_p2sh_p2wsh(program) if encode_p2sh else script_to_p2wsh(program)
      else:
          addr = key_to_p2sh_p2wpkh(pubkey) if encode_p2sh else key_to_p2wpkh(pubkey)
      if not encode_p2sh:
          assert_equal(node.validateaddress(addr)['scriptPubKey'], witness_script(use_p2wsh, pubkey))
      return node.createrawtransaction([utxo], {addr: amount})
  
  # Create a transaction spending a given utxo to a segwit output corresponding
  # to the given pubkey: use_p2wsh determines whether to use P2WPKH or P2WSH;
  # encode_p2sh determines whether to wrap in P2SH.
  # sign=True will have the given node sign the transaction.
  # insert_redeem_script will be added to the scriptSig, if given.
  def send_to_witness(use_p2wsh, node, utxo, pubkey, encode_p2sh, amount, sign=True, insert_redeem_script=""):
      tx_to_witness = create_witness_tx(node, use_p2wsh, utxo, pubkey, encode_p2sh, amount)
      if (sign):
          signed = node.signrawtransaction(tx_to_witness)
          assert("errors" not in signed or len(["errors"]) == 0)
          return node.sendrawtransaction(signed["hex"])
      else:
          if (insert_redeem_script):
              tx = FromHex(CTransaction(), tx_to_witness)
              tx.vin[0].scriptSig += CScript([hex_str_to_bytes(insert_redeem_script)])
              tx_to_witness = ToHex(tx)
  
      return node.sendrawtransaction(tx_to_witness)
  