#!/usr/bin/env python3
"""Inspect an *address-ordered* VT1200 ROM image.

Expects the image produced by ``reconstruct.py`` in the default (linear) mode,
where file offset == physical byte - 0x07E40000.  Reports the reset vector, the
interrupt vector page and each bank header checksum.

Usage:
    python3 vt1200_map.py vt1200_v22.bin
"""
import struct
import sys

ROM_BASE = 0x07E40000
BANK = 0x40000                 # 256 KiB per EPROM pair
N_BANKS = 7
VECTOR_PAGE = 0x80             # 32 x 32-bit entries at the top of the image


def main(path):
    d = open(path, "rb").read()
    n = len(d)
    print(f"image      : {path}  ({n} bytes = 0x{n:X})")
    print(f"load base  : byte 0x{ROM_BASE:08X}   bit 0x{ROM_BASE << 3:08X}")
    print(f"top byte   : 0x{ROM_BASE + n - 1:08X}   bit 0x{(ROM_BASE + n - 1) << 3:08X}")

    # --- reset vector: last entry of the vector page ---
    rv = struct.unpack_from("<I", d, n - 4)[0]
    tgt = rv >> 3
    off = tgt - ROM_BASE
    where = f"file 0x{off:06X}" if 0 <= off < n else "OUT OF RANGE"
    print(f"\nreset vector: 0x{rv:08X}  -> byte 0x{tgt:08X} ({where})")
    print(f"              [8:16] = {d[8:16].hex(' ')}")

    # --- interrupt vector page (last 128 bytes) ---
    print(f"\nvector page @ file 0x{n - VECTOR_PAGE:06X} "
          f"(logical bit 0xFFFFFC00..0xFFFFFFFF):")
    base = n - VECTOR_PAGE
    for k in range(VECTOR_PAGE // 4):
        v = struct.unpack_from("<I", d, base + 4 * k)[0]
        o = (v >> 3) - ROM_BASE
        tag = f"-> file 0x{o:06X}" if 0 <= o < n else f"(0x{v:08X})"
        print(f"  vec{k:2d} = 0x{v:08X}  {tag}")

    # --- per-bank header: [checksum16][?][0xAAAA][0x5555] ---
    print("\nbank headers (h0 = 16-bit word sum from the magic word to bank end):")
    for b in range(N_BANKS):
        off = b * BANK
        h0, h1 = struct.unpack_from("<HH", d, off)
        words = struct.unpack_from(f"<{(BANK - 4) // 2}H", d, off + 4)
        s = sum(words) & 0xFFFF
        print(f"  bank {b}  byte 0x{ROM_BASE + off:08X}"
              f"  hdr=0x{h0:04X} 0x{h1:04X} aaaa 5555"
              f"  sum=0x{s:04X}  checksum_ok={s == h0}")


if __name__ == "__main__":
    if len(sys.argv) != 2:
        raise SystemExit(__doc__)
    main(sys.argv[1])