import hashlib

def hash256(data):
    """Bitcoin's Double-SHA256."""
    first_pass = hashlib.sha256(data).digest()
    return hashlib.sha256(first_pass).digest()

def get_merkle_root(txids):
    """
    Recursively calculates the Merkle Root from a list of TXIDs.
    TXIDs should be in hex format.
    """
    if not txids:
        return None

    # 1. Convert hex TXIDs to bytes (Little-Endian)
    hashes = [bytes.fromhex(tx)[::-1] for tx in txids]

    while len(hashes) > 1:
        # 2. Handle Odd Count (Duplication Rule)
        if len(hashes) % 2 != 0:
            hashes.append(hashes[-1])

        new_level = []
        # 3. Pair and Hash
        for i in range(0, len(hashes), 2):
            # Concatenate pair and hash twice
            combined = hashes[i] + hashes[i+1]
            new_level.append(hash256(combined))

        hashes = new_level

    # 4. Return result as Big-Endian Hex for display
    return hashes[0][::-1].hex()

# --- Simulation ---

# Block 800,000 Sample TXIDs (Simplified)
tx_list = [
    "5231c6298642289c02d645938986a7d5e69e46a9a08e7514a34f4929a0e698a9", # Coinbase
    "f182c62c3f769f36f3323c276f7f2b6e8a4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f", # TX 1
    "d5a4c3b2a1f0e9d8c7b6a594837261504a3b2c1d0e9f8a7b6c5d4e3f2a1b0c9d"  # TX 2 (Odd count!)
]

print(f"--- Calculating Merkle Root for {len(tx_list)} Transactions ---")
root = get_merkle_root(tx_list)

print(f"[*] Generated Merkle Root: {root}")
print(f"[*] Correct Length: {len(root)} chars (32 bytes)")