rom.py

from collections.abc import Buffer

from modes import Addr


class Rom(Buffer):
    """
    Byte buffer with known address-offset.
    """

    _data: bytearray
    _start: Addr
    _size: int

    def __init__(self, *, size: int, start: Addr, init: bytearray | None = None):
        self._start = start
        self._size = size

        if init:
            init.resize(size)
            self._data = init
        else:
            self._data = bytearray(size)

    def __getitem__(self, addr: Addr) -> int:
        return self._data[addr - self._start]

    def __setitem__(self, addr: Addr, value: int | Addr) -> None:
        if not isinstance(value, Addr):
            self._data[addr - self._start] = value
        else:
            self._data[addr - self._start] = value & 0xFF
            self._data[addr - self._start + 1] = value >> 8

    def __buffer__(self, flags: int) -> memoryview:
        return self._data.__buffer__(flags)