import sys
import os.path

floppy_bytes = 1440 * 1024
sector_bytes = 512
dirent_bytes = 32
file_bytes = sector_bytes * 128

floppy = bytearray()

def extend_padded(buffer, alignment, data):
	padding_len = (alignment - len(data)) % alignment
	buffer.extend(data)
	buffer.extend(bytes(padding_len))

if len(sys.argv) < 3:
	print(f'Usage: {sys.argv[0]} disk.img bootsector.bin files…', file=sys.stderr)
	sys.exit(1)

output_path = sys.argv[1]
bootsector_path = sys.argv[2]
files_paths = sys.argv[3:]

with open(bootsector_path, 'rb') as f:
	bootsector = f.read()
assert len(bootsector) == sector_bytes
floppy.extend(bootsector)

files = []
directory = bytearray()

for file_path in files_paths:
	with open(file_path, 'rb') as f:
		file_contents = f.read()
	assert len(file_contents) <= 128 * sector_bytes # 128 sector files
	files.append(file_contents)

	# dirent:
	#  2 bytes size in 512B sectors, 0 for end of listing
	#  30 bytes null-terminated name
	sectors = (len(file_contents) + sector_bytes - 1) // sector_bytes
	file_name = os.path.basename(file_path).encode() + b'\0'
	assert len(file_name) <= 30
	dirent = bytes([sectors & 0xff, sectors >> 8]) + file_name
	extend_padded(directory, dirent_bytes, dirent)

## Add a zero dirent to mark the end of the directory
## (and the start of the consulate)
#directory.extend(bytes(dirent_bytes))

assert len(directory) <= sector_bytes

extend_padded(floppy, sector_bytes, directory)

for file_contents in files:
	extend_padded(floppy, file_bytes, file_contents)

assert len(floppy) <= floppy_bytes

output = bytearray()
extend_padded(output, floppy_bytes, floppy)

with open(output_path, 'wb') as f:
	f.write(output)