#!/usr/bin/env python3
import struct

def calc_bootblock_checksum(data):
    """Calculate Amiga bootblock checksum"""
    # Clear checksum field first
    data = bytearray(data)
    struct.pack_into('>I', data, 4, 0)
    
    # Sum all longwords with carry
    chksum = 0
    for i in range(0, 1024, 4):
        val = struct.unpack_from('>I', data, i)[0]
        chksum += val
        if chksum > 0xFFFFFFFF:
            chksum = (chksum & 0xFFFFFFFF) + 1
    
    # Return NOT of sum
    chksum = (~chksum) & 0xFFFFFFFF
    return chksum

# Read files
with open('boot.bin', 'rb') as f:
    boot = bytearray(f.read())

with open('game.bin', 'rb') as f:
    game = f.read()

# Pad bootblock to 1024 bytes
if len(boot) < 1024:
    boot += b'\x00' * (1024 - len(boot))

# Calculate and set checksum
chksum = calc_bootblock_checksum(boot)
struct.pack_into('>I', boot, 4, chksum)
print(f"Bootblock checksum: 0x{chksum:08X}")

# Create ADF
adf = bytearray(880 * 1024)
adf[0:1024] = boot
adf[1024:1024+len(game)] = game

# Write ADF
with open('giochino.adf', 'wb') as f:
    f.write(adf)

print(f"Created giochino.adf ({len(adf)} bytes)")
print(f"Game size: {len(game)} bytes")