"""
coax.serial_interface
~~~~~~~~~~~~~~~~~~~~~
"""

import time
import os
import struct
from copy import copy
from contextlib import contextmanager
from serial import Serial, SerialException
from sliplib import SlipWrapper, ProtocolError

from .interface import Interface, InterfaceFeature, normalize_frame
from .exceptions import InterfaceError, InterfaceTimeout, ReceiveError, ReceiveTimeout

class SerialInterface(Interface):
    """Serial attached 3270 coax interface."""

    def __init__(self, serial):
        if serial is None:
            raise ValueError('Serial port is required')

        super().__init__()

        self.serial = serial

        self.slip_serial = SlipSerial(self.serial)

        self.legacy_firmware_detected = None
        self.legacy_firmware_version = None

    def reset(self):
        """Reset the interface."""
        original_serial_timeout = self.serial.timeout

        self.serial.timeout = 5

        self.serial.reset_input_buffer()

        self._write_message(bytes([0x01]))

        try:
            message = self._read_message()
        finally:
            self.serial.timeout = original_serial_timeout

            self.serial.reset_input_buffer()

        if message[0] != 0x01:
            raise _convert_error(message)

        if message[1:] == b'\x32\x70':
            self.legacy_firmware_detected = False
            self.legacy_firmware_version = None
        elif len(message) == 4:
            (major, minor, patch) = struct.unpack('BBB', message[1:])

            self.legacy_firmware_detected = True
            self.legacy_firmware_version = f'{major}.{minor}.{patch}'
        else:
            raise InterfaceError(f'Invalid reset response: {message}')

        # Query features, if this is not a legacy firmware.
        if not self.legacy_firmware_detected:
            try:
                self.features = self._get_features()
            except InterfaceError:
                pass

    def enter_dfu_mode(self):
        """Enter device firmware upgrade mode."""
        message = bytes([0xf2])

        self._write_message(message)

        message = self._read_message()

        if message[0] != 0x01:
            raise _convert_error(message)

    def _get_features(self):
        """Get interface features."""
        message = bytes([0xf0, 0x07])

        self._write_message(message)

        message = self._read_message()

        if message[0] != 0x01:
            raise _convert_error(message)

        known_feature_values = {feature.value for feature in InterfaceFeature}

        features = {InterfaceFeature(value) for value in message[1:] if value in known_feature_values}

        return features

    def _transmit_receive(self, outbound_frames, response_lengths, timeout):
        if len(response_lengths) != len(outbound_frames):
            raise ValueError('Response lengths length must equal outbound frames length')

        if any(address is not None for (address, _) in outbound_frames) and InterfaceFeature.PROTOCOL_3299 not in self.features:
            raise NotImplementedError('Interface does not support 3299 protocol')

        # Pack all messages before sending.
        timeout_milliseconds = self._calculate_timeout_milliseconds(timeout)

        messages = [_pack_transmit_receive_message(address, frame, response_length, timeout_milliseconds)
                    for ((address, frame), response_length) in zip(outbound_frames, response_lengths)]

        responses = []

        for message in messages:
            self._write_message(message)

            message = self._read_message()

            if message[0] == 0x01:
                response = _unpack_transmit_receive_response(message[1:])
            else:
                error = _convert_error(message)

                if not isinstance(error, (ReceiveError, ReceiveTimeout)):
                    raise error

                response = error

            responses.append(response)

        return responses

    def _calculate_timeout_milliseconds(self, timeout):
        milliseconds = 0

        if timeout:
            if self.serial.timeout and timeout > self.serial.timeout:
                raise ValueError('Timeout cannot be greater than serial timeout')

            milliseconds = int(timeout * 1000)

        return milliseconds

    def _read_message(self):
        try:
            message = self.slip_serial.recv_msg()
        except ProtocolError:
            raise InterfaceError('SLIP protocol error')

        if len(message) < 4:
            raise InterfaceError(f'Invalid response message: {message}')

        (length,) = struct.unpack('>H', message[:2])

        if length != len(message) - 4:
            raise InterfaceError('Response message length mismatch')

        if length < 1:
            raise InterfaceError('Empty response message')

        return message[2:-2]

    def _write_message(self, message):
        self.slip_serial.send_msg(struct.pack('>H', len(message)) + message +
                                  struct.pack('>H', 0))

@contextmanager
def open_serial_interface(serial_port, reset=True):
    """Opens serial port and initializes serial attached 3270 coax interface."""
    with WindowsSafeSerial(serial_port, 115200) as serial:
        serial.reset_input_buffer()
        serial.reset_output_buffer()

        # Allow the interface firmware time to start, this is only required for the
        # original Arduino Mega based interface.
        if 'COAX_FAST_START' not in os.environ:
            time.sleep(3)

        interface = SerialInterface(serial)

        if reset:
            interface.reset()

        yield interface

def _pack_transmit_receive_message(address, frame, response_length, timeout_milliseconds):
    # Convert the three frame formats to a simple list of 10-bit words with
    # a repeat count and offset.
    (words, repeat_count, repeat_offset) = normalize_frame(address, frame)

    message = bytes([0x06])

    # NOTE: Although the frame normalization routine may result in a repeat
    # offset greater than 1 if an addressed WORD_DATA frame has a repeat
    # count, this WILL fail to be packed below as it will overflow the
    # unsigned short field here. Today, oec does not use a repeat with an
    # addressed WORD_DATA frame as the "jumbo write" function will always
    # expand addressed frames.
    message += struct.pack('>H', (repeat_offset << 15) | repeat_count)

    # Set the 3299 mode flag.
    if address is not None:
        words[0] |= 0x8000

    for word in words:
        message += struct.pack('<H', word)

    message += struct.pack('>HH', response_length, timeout_milliseconds)

    return message

def _unpack_transmit_receive_response(bytes_):
    return [(hi << 8) | lo for (lo, hi) in zip(bytes_[::2], bytes_[1::2])]

ERROR_MAP = {
    1: InterfaceError('Invalid request message'),
    2: InterfaceError('Unknown command'),

    101: InterfaceError('Receiver active'),
    102: ReceiveTimeout(),
    103: ReceiveError('Receiver buffer overflow'),
    104: ReceiveError('Receiver error')
}

def _convert_error(message):
    if message[0] != 0x02:
        return InterfaceError(f'Invalid response: {message}')

    if len(message) < 2:
        return InterfaceError(f'Invalid error response: {message}')

    if message[1] in ERROR_MAP:
        error = copy(ERROR_MAP[message[1]])

        # Append description if included.
        if len(message) > 2:
            description = message[2:].decode('ascii')

            if error.args:
                error.args = (f'{error.args[0]}: {description}', *error.args[1:])
            else:
                error.args = (description,)

        return error

    return InterfaceError(f'Unknown error: {message[1]}')

class SlipSerial(SlipWrapper):
    """sliplib wrapper for pySerial."""

    def send_bytes(self, packet):
        """Sends a packet over the serial port."""
        self.stream.write(packet)
        self.stream.flush()

    def recv_bytes(self):
        """Receive data from the serial port."""
        if self.stream.closed:
            return b''

        count = self.stream.in_waiting

        if count:
            return self.stream.read(count)

        byte = self.stream.read(1)

        if byte == b'':
            raise InterfaceTimeout()

        return byte

# Based on workaround detailed in https://github.com/pyserial/pyserial/issues/362
class WindowsSafeSerial(Serial):
    def _reconfigure_port(self, *args, **kwargs):
        try:
            super()._reconfigure_port(*args, **kwargs)
        except SerialException as error:
            if not self._is_windows_open_error(error):
                raise

    def _is_windows_open_error(self, error):
        message = str(error)

        if os.name == 'nt' and 'OSError(22, \'The parameter is incorrect.\', None, 87)' in message:
            return True

        return False