"""LowCmd 序列化 (PRO 格式 616B + Blowfish 加密).

PRO 格式跟 free-dog-sdk EDU 版的关键差异:
  - 总长 616B (EDU 614B)
  - CRC 偏移 612..616 (EDU 在 610..614)
  - CRC 前有 2 字节 0x0000 固定填充 (位置 610..612)
  - CRC 算法用裸 gen_crc, 不 XOR (EDU 用 encryptCrc XOR 0xedcab9de)
  - bandWidth 字节序是 BE (EDU 用 LE)
  - SN/version 全 0 (EDU 填实际值)

发送前必须 Blowfish 加密 (MCU 期待加密数据).

布局表 (616 字节明文):
  offset  bytes 字段
  0..2    2     head 0xfeef
  2..3    1     levelFlag 0xff
  3..4    1     frameReserve
  4..12   8     SN (全 0)
  12..20  8     version (全 0)
  20..22  2     bandWidth 0x3ac0 BE
  22..562 540   motorCmd[20] × 27B
  562..566 4    bms (全 0)
  566..606 40   wirelessRemote (全 0)
  606..610 4    reserve (全 0)
  610..612 2    固定填充 0x0000
  612..616 4    CRC = gen_crc(cmd[:612])
"""
import struct
from typing import Optional
from ..types.low_cmd import LowCmd
from ..types.motor import MotorCmd
from ..utils.common import gen_crc
from .blowfish import Blowfish


def build_low_cmd_plain(lowcmd: LowCmd) -> bytes:
    """构造 PRO 格式 616B 明文 LowCmd."""
    cmd = bytearray(616)

    # 0..2  head
    cmd[0:2] = lowcmd.head
    # 2..3  levelFlag
    cmd[2] = lowcmd.levelFlag
    # 3..4  frameReserve
    cmd[3] = lowcmd.frameReserve
    # 4..12 SN
    cmd[4:12] = lowcmd.SN
    # 12..20 version
    cmd[12:20] = lowcmd.version
    # 20..22 bandWidth BE
    cmd[20:22] = struct.pack('>H', lowcmd.bandWidth)
    # 22..562 motorCmd[20] × 27B
    offset = 22
    for motor in lowcmd.motorCmd:
        motor_bytes = motor.to_bytes()
        assert len(motor_bytes) == 27, f'motorCmd 序列化长度错: {len(motor_bytes)}'
        cmd[offset:offset + 27] = motor_bytes
        offset += 27
    # 562..566 bms (默认 0)
    # 566..606 wirelessRemote
    cmd[566:606] = lowcmd.wirelessRemote
    # 606..610 reserve
    cmd[606:610] = lowcmd.reserve
    # 610..612 固定填充 0x0000
    # 612..616 CRC
    cmd[612:616] = gen_crc(memoryview(cmd)[:612])

    return bytes(cmd)


def build_low_cmd_encrypted(lowcmd: LowCmd, bf: Blowfish) -> bytes:
    """构造并加密 LowCmd (PRO 真实发包格式).

    Returns:
        616 字节 Blowfish ECB 密文, 直接 sendto MCU :8007.
    """
    plain = build_low_cmd_plain(lowcmd)
    return bf.encrypt_ecb(plain)


def make_damping_cmd() -> LowCmd:
    """快捷: 全 damping 的 LowCmd (常用于初始化/紧急停)."""
    cmd = LowCmd()
    cmd.all_damping()
    return cmd