"""Validate the PM35 RAM-load SCI8 image against the selected EEPROM profile."""
import argparse
from pathlib import Path
import struct


def check_image(path, eeprom):
    data = path.read_bytes()
    limit = {"AT25256B": 32508, "M95M02": 261884}[eeprom]
    if not 24 <= len(data) <= limit:
        raise ValueError(f"Image size {len(data)} outside 24..{limit}")
    if struct.unpack_from("<H", data)[0] != 0x08AA:
        raise ValueError("Not a SCI8 boot image")
    high, low = struct.unpack_from("<HH", data, 18)
    entry = (high << 16) | low
    position, blocks = 22, []
    while True:
        if position + 2 > len(data):
            raise ValueError("Missing boot terminator")
        words = struct.unpack_from("<H", data, position)[0]
        position += 2
        if not words:
            if position != len(data):
                raise ValueError("Trailing bytes after boot terminator")
            break
        if position + 4 + words * 2 > len(data):
            raise ValueError("Truncated boot block")
        high, low = struct.unpack_from("<HH", data, position)
        address = (high << 16) | low
        end = address + words
        if not 0x8000 <= address < end <= 0xD000:
            raise ValueError(f"Boot destination {address:#x}..{end:#x} outside code RAM")
        if any(address < old_end and old_start < end for old_start, old_end in blocks):
            raise ValueError("Overlapping boot blocks")
        blocks.append((address, end))
        position += 4 + words * 2
    if not any(start <= entry < end for start, end in blocks):
        raise ValueError("Entry point not loaded by the boot table")
    return len(data), len(blocks), limit - len(data)


if __name__ == "__main__":
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("image", type=Path)
    parser.add_argument("--eeprom", choices=("AT25256B", "M95M02"), required=True)
    args = parser.parse_args()
    size, blocks, free = check_image(args.image, args.eeprom)
    print(f"PASS SCI8 {args.eeprom}: {size} bytes, {blocks} RAM blocks, {free} bytes free")