import os
import fcntl
import math
import time
import struct
import logging
import threading
from contextlib import contextmanager
from functools import reduce
from typing import List

from .base import BaseHandle

try:
  import spidev
except ImportError:
  spidev = None

# Constants
SYNC = 0x5A
HACK = 0x79
DACK = 0x85
NACK = 0x1F
CHECKSUM_START = 0xAB

ACK_TIMEOUT_SECONDS = 0.1
MAX_XFER_RETRY_COUNT = 5

USB_MAX_SIZE = 0x40

DEV_PATH = "/dev/spidev0.0"


class PandaSpiException(Exception):
  pass

class PandaSpiUnavailable(PandaSpiException):
  pass

class PandaSpiNackResponse(PandaSpiException):
  pass

class PandaSpiMissingAck(PandaSpiException):
  pass

class PandaSpiBadChecksum(PandaSpiException):
  pass

class PandaSpiTransferFailed(PandaSpiException):
  pass


SPI_LOCK = threading.Lock()

class SpiDevice:
  """
  Provides locked, thread-safe access to a panda's SPI interface.
  """
  def __init__(self, speed=30000000):
    if not os.path.exists(DEV_PATH):
      raise PandaSpiUnavailable(f"SPI device not found: {DEV_PATH}")
    if spidev is None:
      raise PandaSpiUnavailable("spidev is not installed")

    self._spidev = spidev.SpiDev()  # pylint: disable=c-extension-no-member
    self._spidev.open(0, 0)
    self._spidev.max_speed_hz = speed

  @contextmanager
  def acquire(self):
    try:
      SPI_LOCK.acquire()
      fcntl.flock(self._spidev, fcntl.LOCK_EX)
      yield self._spidev
    finally:
      fcntl.flock(self._spidev, fcntl.LOCK_UN)
      SPI_LOCK.release()

  def close(self):
    self._spidev.close()


class PandaSpiHandle(BaseHandle):
  """
  A class that mimics a libusb1 handle for panda SPI communications.
  """
  def __init__(self):
    self.dev = SpiDevice()

  # helpers
  def _calc_checksum(self, data: List[int]) -> int:
    cksum = CHECKSUM_START
    for b in data:
      cksum ^= b
    return cksum

  def _wait_for_ack(self, spi, ack_val: int) -> None:
    start = time.monotonic()
    while (time.monotonic() - start) < ACK_TIMEOUT_SECONDS:
      dat = spi.xfer2(b"\x12")[0]
      if dat == NACK:
        raise PandaSpiNackResponse
      elif dat == ack_val:
        return

    raise PandaSpiMissingAck

  def _transfer(self, spi, endpoint: int, data, max_rx_len: int = 1000) -> bytes:
    logging.debug("starting transfer: endpoint=%d, max_rx_len=%d", endpoint, max_rx_len)
    logging.debug("==============================================")

    exc = PandaSpiException()
    for n in range(MAX_XFER_RETRY_COUNT):
      logging.debug("\ntry #%d", n+1)
      try:
        logging.debug("- send header")
        packet = struct.pack("<BBHH", SYNC, endpoint, len(data), max_rx_len)
        packet += bytes([reduce(lambda x, y: x^y, packet) ^ CHECKSUM_START])
        spi.xfer2(packet)

        logging.debug("- waiting for header ACK")
        self._wait_for_ack(spi, HACK)

        # send data
        logging.debug("- sending data")
        packet = bytes([*data, self._calc_checksum(data)])
        spi.xfer2(packet)

        logging.debug("- waiting for data ACK")
        self._wait_for_ack(spi, DACK)

        # get response length, then response
        response_len_bytes = bytes(spi.xfer2(b"\x00" * 2))
        response_len = struct.unpack("<H", response_len_bytes)[0]

        logging.debug("- receiving response")
        dat = bytes(spi.xfer2(b"\x00" * (response_len + 1)))
        if self._calc_checksum([DACK, *response_len_bytes, *dat]) != 0:
          raise PandaSpiBadChecksum

        return dat[:-1]
      except PandaSpiException as e:
        exc = e
        logging.debug("SPI transfer failed, %d retries left", n, exc_info=True)
    raise exc

  # libusb1 functions
  def close(self):
    self.dev.close()

  def controlWrite(self, request_type: int, request: int, value: int, index: int, data, timeout: int = 0):
    with self.dev.acquire() as spi:
      return self._transfer(spi, 0, struct.pack("<BHHH", request, value, index, 0))

  def controlRead(self, request_type: int, request: int, value: int, index: int, length: int, timeout: int = 0):
    with self.dev.acquire() as spi:
      return self._transfer(spi, 0, struct.pack("<BHHH", request, value, index, length))

  # TODO: implement these properly
  def bulkWrite(self, endpoint: int, data: List[int], timeout: int = 0) -> int:
    with self.dev.acquire() as spi:
      for x in range(math.ceil(len(data) / USB_MAX_SIZE)):
        self._transfer(spi, endpoint, data[USB_MAX_SIZE*x:USB_MAX_SIZE*(x+1)])
      return len(data)

  def bulkRead(self, endpoint: int, length: int, timeout: int = 0) -> bytes:
    ret: List[int] = []
    with self.dev.acquire() as spi:
      for _ in range(math.ceil(length / USB_MAX_SIZE)):
        d = self._transfer(spi, endpoint, [], max_rx_len=USB_MAX_SIZE)
        ret += d
        if len(d) < USB_MAX_SIZE:
          break
    return bytes(ret)