"""Build a ColecoVision/Adam cartridge ROM (.col) holding the Z80 viewer + image.

Cartridge maps at $8000.  Header: magic $55 $AA (skip the Coleco title screen and
run immediately), eight pointer words, then a table of JP vectors -- the BIOS
jumps to the one at $800A (the game entry).  We point that at our viewer; the RST
and interrupt vectors go to a stub (we run with interrupts disabled).
"""

from __future__ import annotations

import struct

from . import viewer

CART_BASE = 0x8000
CART_SIZE = 0x2000           # 8 KB (viewer + 6912-byte image fit comfortably)
VECTORS = 8                  # entry + 7 RST/INT stubs
CODE_BASE = CART_BASE + 10 + VECTORS * 3      # after magic(2)+ptrs(8)+vectors


def build_rom(data: bytes, display: str = "forever", seconds: int = 0) -> bytes:
    if len(data) != viewer.PATTERN_BYTES + viewer.NCELLS:
        raise ValueError(f"unexpected image length {len(data)}")

    vk = dict(display=display, seconds=seconds)
    code = viewer.build(CODE_BASE, 0, **vk)          # pass 1: measure code length
    data_addr = CODE_BASE + len(code) + 1            # +1 for the stub RET
    code = viewer.build(CODE_BASE, data_addr, **vk)  # pass 2: real data address
    stub_addr = CODE_BASE + len(code)
    data_addr = stub_addr + 1

    if data_addr - CART_BASE + len(data) > CART_SIZE:
        raise ValueError("viewer + image exceed the 8KB cartridge")

    header = bytearray([0x55, 0xAA]) + bytes(8)      # magic + 8 pointer bytes
    vecs = bytearray()
    targets = [CODE_BASE] + [stub_addr] * (VECTORS - 1)
    for t in targets:
        vecs += bytes([0xC3]) + struct.pack("<H", t)  # JP t

    rom = bytearray(header + vecs + code + bytes([0xC9]))   # stub = RET
    rom += bytes(data)
    return bytes(rom) + bytes(CART_SIZE - len(rom))


def write_col(rom: bytes, path: str) -> str:
    with open(path, "wb") as f:
        f.write(rom)
    return path