#!/usr/bin/env python3

# Copyright (C) 2014 The python-bitcoinlib developers
#
# This file is part of python-bitcoinlib.
#
# It is subject to the license terms in the LICENSE file found in the top-level
# directory of this distribution.
#
# No part of python-bitcoinlib, including this file, may be copied, modified,
# propagated, or distributed except according to the terms contained in the
# LICENSE file.

"""Low-level example of how to spend a P2WSH/BIP141 txout"""

import hashlib

from bitcoin import SelectParams
from bitcoin.core import b2x, lx, COIN, COutPoint, CMutableTxOut, CMutableTxIn, CMutableTransaction, CTxInWitness, CTxWitness
from bitcoin.core.script import CScript, CScriptWitness, OP_0, OP_CHECKSIG, SignatureHash, SIGHASH_ALL, SIGVERSION_WITNESS_V0
from bitcoin.wallet import CBitcoinSecret, CBitcoinAddress, P2WSHBitcoinAddress

SelectParams('testnet')

# Create the (in)famous correct brainwallet secret key.
h = hashlib.sha256(b'correct horse battery staple').digest()
seckey = CBitcoinSecret.from_secret_bytes(h)

# Create a witnessScript and corresponding redeemScript. Similar to a scriptPubKey
# the redeemScript must be satisfied for the funds to be spent.
txin_redeemScript = CScript([seckey.pub, OP_CHECKSIG])
txin_scriptHash = hashlib.sha256(txin_redeemScript).digest()
txin_scriptPubKey = CScript([OP_0, txin_scriptHash])


# Convert the P2WSH scriptPubKey to a base58 Bitcoin address and print it.
# You'll need to send some funds to it to create a txout to spend.
txin_p2wsh_address = P2WSHBitcoinAddress.from_scriptPubKey(txin_scriptPubKey)
print('Pay to:', str(txin_p2wsh_address))

# Same as the txid:vout the createrawtransaction RPC call requires
# lx() takes *little-endian* hex and converts it to bytes; in Bitcoin
# transaction hashes are shown little-endian rather than the usual big-endian.
txid = lx('ace9dc7c987a52266e38fe8544c2d12182401341c98d151f4b394cf69aa5c3e5')
vout = 0

# Specify the amount send to your P2WSH address.
amount = int(0.0001 * COIN)

# Calculate an amount for the upcoming new UTXO. Set a high fee (5%) to bypass
# bitcoind minfee setting.
amount_less_fee = amount * 0.95

# Create the txin structure, which includes the outpoint. The scriptSig
# defaults to being empty as is necessary for spending a P2WSH output.
txin = CMutableTxIn(COutPoint(txid, vout))


# Specify a destination address and create the txout.
destination_address = CBitcoinAddress(
    '2NGZrVvZG92qGYqzTLjCAewvPZ7JE8S8VxE').to_scriptPubKey()
txout = CMutableTxOut(amount_less_fee, destination_address)

# Create the unsigned transaction.
tx = CMutableTransaction([txin], [txout])

# Calculate the signature hash for that transaction.
sighash = SignatureHash(script=txin_redeemScript, txTo=tx, inIdx=0,
                        hashtype=SIGHASH_ALL, amount=amount, sigversion=SIGVERSION_WITNESS_V0)

# Now sign it. We have to append the type of signature we want to the end, in
# this case the usual SIGHASH_ALL.
sig = seckey.sign(sighash) + bytes([SIGHASH_ALL])


# # Construct a witness for this P2WSH transaction and add to tx.
witness = CScriptWitness([sig, txin_redeemScript])
tx.wit = CTxWitness([CTxInWitness(witness)])

# TODO: upgrade VerifyScript to support Segregated Witness and place verify the witness program here.

# Done! Print the transaction to standard output with the bytes-to-hex
# function.
print(b2x(tx.serialize()))