#!/usr/bin/env python3
"""Pack/unpack 4-byte LE sensor reports and slot/config replies."""
from __future__ import annotations

from dataclasses import dataclass
from typing import Optional, Tuple

BATT_UNKNOWN = 0xFF
DIST_NO_TARGET = 0xFFFF
SLOT_UNASSIGNED = 0xFF

FLAG_LOW_BATT = 0x01
FLAG_FAULT = 0x02
FLAG_NO_TARGET = 0x04
FLAG_UNCHANGED = 0x08

CFG_JOIN_OPEN = 0x01
CFG_POOL_FULL = 0x02
CFG_BUSY = 0x04


@dataclass(frozen=True)
class SensorReport:
    battery: int
    flags: int
    dist: int


@dataclass(frozen=True)
class SlotConfig:
    slot: int
    flags: int
    period_s: int


def unpack_report(data: bytes) -> Optional[SensorReport]:
    if data is None or len(data) != 4:
        return None
    battery = data[0]
    flags = data[1]
    dist = data[2] | (data[3] << 8)
    return SensorReport(battery=battery, flags=flags, dist=dist)


def pack_report(battery: int, flags: int, dist: int) -> bytes:
    batt = max(0, min(255, int(battery))) & 0xFF
    fl = int(flags) & 0xFF
    d = max(0, min(0xFFFF, int(dist))) & 0xFFFF
    return bytes((batt, fl, d & 0xFF, (d >> 8) & 0xFF))


def unpack_slot_config(data: bytes) -> Optional[SlotConfig]:
    if data is None or len(data) != 4:
        return None
    slot = data[0]
    flags = data[1]
    period = data[2] | (data[3] << 8)
    return SlotConfig(slot=slot, flags=flags, period_s=period)


def pack_slot_config(slot: int, flags: int, period_s: int) -> bytes:
    s = max(0, min(255, int(slot))) & 0xFF
    fl = int(flags) & 0xFF
    p = max(0, min(0xFFFF, int(period_s))) & 0xFFFF
    return bytes((s, fl, p & 0xFF, (p >> 8) & 0xFF))


def report_to_bytes(r: SensorReport) -> bytes:
    return pack_report(r.battery, r.flags, r.dist)


def pack_interval_min(minutes: int) -> bytes:
    """2-byte LE uint16 report interval in minutes."""
    m = max(1, min(0xFFFF, int(minutes))) & 0xFFFF
    return bytes((m & 0xFF, (m >> 8) & 0xFF))


def unpack_interval_min(data: bytes) -> Optional[int]:
    if data is None or len(data) != 2:
        return None
    return data[0] | (data[1] << 8)