#!/usr/bin/env python3
"""Build Berger/JBD BLE frames observed in the Android app."""

from __future__ import annotations

import argparse


def checksum(command: int, payload: bytes = b"") -> int:
    """JBD two's-complement checksum over command, length, and payload."""
    total = (command + len(payload) + sum(payload)) & 0xFFFF
    return ((total ^ 0xFFFF) + 1) & 0xFFFF


def frame(mode: int, command: int, payload: bytes = b"") -> bytes:
    check = checksum(command, payload)
    return bytes([0xDD, mode, command, len(payload), *payload, check >> 8, check & 0xFF, 0x77])


def read_frame(command: int) -> bytes:
    return frame(0xA5, command)


def write_frame(command: int, payload: bytes) -> bytes:
    return frame(0x5A, command, payload)


def name_frame(command: int, payload: bytes = b"") -> bytes:
    check = (command + len(payload) + sum(payload)) & 0xFF
    return bytes([0xFF, 0xAA, command, len(payload), *payload, check])


def parse_hex_bytes(value: str) -> bytes:
    clean = value.replace(" ", "").replace(":", "")
    return bytes.fromhex(clean)


def main() -> None:
    parser = argparse.ArgumentParser()
    sub = parser.add_subparsers(dest="cmd", required=True)

    p_read = sub.add_parser("read")
    p_read.add_argument("command", type=lambda x: int(x, 0))

    p_write = sub.add_parser("write")
    p_write.add_argument("command", type=lambda x: int(x, 0))
    p_write.add_argument("payload_hex", nargs="?", default="")

    p_name = sub.add_parser("name")
    p_name.add_argument("value")

    args = parser.parse_args()
    if args.cmd == "read":
        print(read_frame(args.command).hex().upper())
    elif args.cmd == "write":
        print(write_frame(args.command, parse_hex_bytes(args.payload_hex)).hex().upper())
    elif args.cmd == "name":
        print(name_frame(0x07, args.value.encode("ascii")).hex().upper())


if __name__ == "__main__":
    main()