btc-transaction-builder.py

import requests
from bit import Key
from bit.network import NetworkAPI

def get_user_input():
    print("🟢 Bitcoin Transaction Builder")
    wif = input("Enter your private key (WIF format): ").strip()
    recipient = input("Enter recipient address: ").strip()
    amount = float(input("Enter amount to send (BTC): ").strip())
    fee = float(input("Enter transaction fee (BTC): ").strip())
    return wif, recipient, amount, fee

def fetch_utxos(address):
    print("🔍 Fetching UTXOs...")
    url = f'https://blockstream.info/api/address/{address}/utxo'
    response = requests.get(url)
    if response.status_code != 200:
        raise Exception("Failed to fetch UTXOs from Blockstream API.")
    return response.json()

def build_transaction(wif, recipient, amount, fee):
    key = Key(wif)
    sender_address = key.address
    utxos = fetch_utxos(sender_address)

    inputs = []
    total_input = 0
    for utxo in utxos:
        inputs.append({
            'txid': utxo['txid'],
            'vout': utxo['vout'],
            'value': utxo['value'] / 1e8  # Convert from satoshis to BTC
        })
        total_input += utxo['value'] / 1e8
        if total_input >= amount + fee:
            break

    if total_input < amount + fee:
        raise Exception("Not enough balance to cover amount + fee.")

    outputs = [
        (recipient, amount, 'btc'),
    ]

    change = round(total_input - amount - fee, 8)
    if change > 0:
        outputs.append((sender_address, change, 'btc'))

    print("✍️ Signing and creating transaction...")
    tx_hex = key.create_transaction(
        outputs=outputs,
        unspents=key.get_unspents(),  # Optional: Use our UTXOs
        fee=fee,
        leftover=sender_address,
    )
    return tx_hex

def main():
    try:
        wif, recipient, amount, fee = get_user_input()
        tx = build_transaction(wif, recipient, amount, fee)
        print("\n✅ Transaction Created!")
        print("Raw TX (hex):")
        print(tx)
        print("\n💡 You can broadcast this via: https://blockstream.info/pushtx")
    except Exception as e:
        print(f"❌ Error: {str(e)}")

if __name__ == "__main__":
    main()