#!/usr/bin/env python3

import re
import sys
import argparse


ROMSIZE = 512 * 1024


class FileMap:

    def __init__(self, base: int, filename: str):
        self.base = base
        self.filename = filename
        with open(filename, 'rb') as f:
            self.data = f.read()
        if len(self.data) == 0:
            raise AttributeError(f'File {filename} is empty')
        if len(self.data) > 4096:
            raise AttributeError(f'File {filename} exceeds 4KiB')
        self.end = self.base + len(self.data)
        if self.base < 0 or self.end > ROMSIZE:
            raise AttributeError(f'File {filename} out of bounds: {hex(self.base)[2:]}:{hex(self.end-1)[2:]}')
        if self.base & 0x0fff != 0:
            raise AttributeError(f'File {filename} not aligned to 4KiB boundary: {hex(self.base)[2:]}:{hex(self.end-1)[2:]}')

    @staticmethod
    def at(base: int):
        def _filemap(f):
            return FileMap(base, f)
        return _filemap
        

def baseimage(byte):
    b = int(byte, 16)
    return bytearray([b]) * ROMSIZE


def create_image(ns):
    buf = ns.fill
    used = {}
    for m in ns.maps:
        if m.base in used:
            raise KeyError(f'{m.filename} and {used[m.base]} are both mapped at {hex(m.base)[2:]}')
        used[m.base] = m.filename
        buf[m.base:m.end] = m.data
    with open(ns.output, 'wb') as f:
        f.write(buf)


def main():
    ap = argparse.ArgumentParser()
    ap.add_argument('--output', '-o', type=str, metavar='FILE', default='27c040.bin', help='Write image to FILE (default: 27c040.bin)')
    ap.add_argument('--<NNNNN>', type=ValueError, metavar='FILE', help='Map FILE at the 4KiB-aligned sector starting at hex-address NNNNN.')
    ap.add_argument('--fill', '-f', type=baseimage, default='FF', help='Fill unmapped areas with this hex byte (default: FF)')

    # https://stackoverflow.com/a/37367814
    ns, unknown = ap.parse_known_args(sys.argv[1:])
    for arg in unknown:
        m = re.match('^--([0-9a-fA-F]{5})$', arg)
        if m is None:
            continue
        base = int(m.group(1), 16)
        ap.add_argument(arg,  type=FileMap.at(base), dest='maps', action='append')
    ns = ap.parse_args(sys.argv[1:])
            
    create_image(ns)


if __name__ == '__main__':
    main()