import os
import struct
import asyncio
import types

from typing import Dict
from typing import NamedTuple
from typing import Callable
from typing import Type
from typing import Optional
from typing import Any

import pyudev

import aiofiles
import aiofiles.base

from . import aioregion

from .logging import get_logger


# =====
class MsdError(Exception):
    pass


class MsdOperationError(MsdError):
    pass


class MsdIsNotOperationalError(MsdOperationError):
    def __init__(self) -> None:
        super().__init__("Missing path for mass-storage device")


class MsdAlreadyConnectedToPcError(MsdOperationError):
    def __init__(self) -> None:
        super().__init__("Mass-storage is already connected to Server")


class MsdAlreadyConnectedToKvmError(MsdOperationError):
    def __init__(self) -> None:
        super().__init__("Mass-storage is already connected to KVM")


class MsdIsNotConnectedToKvmError(MsdOperationError):
    def __init__(self) -> None:
        super().__init__("Mass-storage is not connected to KVM")


class MsdIsBusyError(MsdOperationError, aioregion.RegionIsBusyError):
    pass


# =====
class _HardwareInfo(NamedTuple):
    manufacturer: str
    product: str
    serial: str


class _ImageInfo(NamedTuple):
    name: str
    size: int
    complete: bool


class _MassStorageDeviceInfo(NamedTuple):
    path: str
    real: str
    size: int
    hw: Optional[_HardwareInfo]
    image: Optional[_ImageInfo]


_IMAGE_INFO_SIZE = 4096
_IMAGE_INFO_MAGIC_SIZE = 16
_IMAGE_INFO_IMAGE_NAME_SIZE = 256
_IMAGE_INFO_PADS_SIZE = _IMAGE_INFO_SIZE - _IMAGE_INFO_IMAGE_NAME_SIZE - 1 - 8 - _IMAGE_INFO_MAGIC_SIZE * 8
_IMAGE_INFO_FORMAT = ">%dL%dc?Q%dx%dL" % (
    _IMAGE_INFO_MAGIC_SIZE,
    _IMAGE_INFO_IMAGE_NAME_SIZE,
    _IMAGE_INFO_PADS_SIZE,
    _IMAGE_INFO_MAGIC_SIZE,
)
_IMAGE_INFO_MAGIC = [0x1ACE1ACE] * _IMAGE_INFO_MAGIC_SIZE


def _make_image_info_bytes(name: str, size: int, complete: bool) -> bytes:
    return struct.pack(
        _IMAGE_INFO_FORMAT,
        *_IMAGE_INFO_MAGIC,
        *memoryview((  # type: ignore
            name.encode("utf-8")
            + b"\x00" * _IMAGE_INFO_IMAGE_NAME_SIZE
        )[:_IMAGE_INFO_IMAGE_NAME_SIZE]).cast("c"),
        complete,
        size,
        *_IMAGE_INFO_MAGIC,
    )


def _parse_image_info_bytes(data: bytes) -> Optional[_ImageInfo]:
    try:
        parsed = list(struct.unpack(_IMAGE_INFO_FORMAT, data))
    except struct.error:
        pass
    else:
        magic_begin = parsed[:_IMAGE_INFO_MAGIC_SIZE]
        magic_end = parsed[-_IMAGE_INFO_MAGIC_SIZE:]
        if magic_begin == magic_end == _IMAGE_INFO_MAGIC:
            image_name_bytes = b"".join(parsed[_IMAGE_INFO_MAGIC_SIZE:_IMAGE_INFO_MAGIC_SIZE + _IMAGE_INFO_IMAGE_NAME_SIZE])
            return _ImageInfo(
                name=image_name_bytes.decode("utf-8", errors="ignore").strip("\x00").strip(),
                size=parsed[_IMAGE_INFO_MAGIC_SIZE + _IMAGE_INFO_IMAGE_NAME_SIZE + 1],
                complete=parsed[_IMAGE_INFO_MAGIC_SIZE + _IMAGE_INFO_IMAGE_NAME_SIZE],
            )
    return None


def _explore_device(device_path: str) -> Optional[_MassStorageDeviceInfo]:
    # udevadm info -a -p  $(udevadm info -q path -n /dev/sda)
    ctx = pyudev.Context()

    device = pyudev.Devices.from_device_file(ctx, device_path)
    if device.subsystem != "block":
        return None
    try:
        size = device.attributes.asint("size") * 512
    except KeyError:
        return None

    hw_info: Optional[_HardwareInfo] = None
    usb_device = device.find_parent("usb", "usb_device")
    if usb_device:
        hw_info = _HardwareInfo(**{
            attr: usb_device.attributes.asstring(attr).strip()
            for attr in ["manufacturer", "product", "serial"]
        })

    with open(device_path, "rb") as device_file:
        device_file.seek(size - _IMAGE_INFO_SIZE)
        image_info = _parse_image_info_bytes(device_file.read())

    return _MassStorageDeviceInfo(
        path=device_path,
        real=os.path.realpath(device_path),
        size=size,
        image=image_info,
        hw=hw_info,
    )


def _msd_operated(method: Callable) -> Callable:
    async def wrap(self: "MassStorageDevice", *args: Any, **kwargs: Any) -> Any:
        if not self._device_path:  # pylint: disable=protected-access
            MsdIsNotOperationalError()
        return (await method(self, *args, **kwargs))
    return wrap


# =====
class MassStorageDevice:  # pylint: disable=too-many-instance-attributes
    def __init__(
        self,
        device_path: str,
        init_delay: float,
        write_meta: bool,
        loop: asyncio.AbstractEventLoop,
    ) -> None:

        self._device_path = device_path
        self.__init_delay = init_delay
        self.__write_meta = write_meta
        self.__loop = loop

        self.__device_info: Optional[_MassStorageDeviceInfo] = None
        self.__saved_device_info: Optional[_MassStorageDeviceInfo] = None
        self.__region = aioregion.AioExclusiveRegion(MsdIsBusyError)
        self.__device_file: Optional[aiofiles.base.AiofilesContextManager] = None
        self.__written = 0

        logger = get_logger(0)
        if self._device_path:
            logger.info("Using %r as mass-storage device", self._device_path)
            try:
                logger.info("Enabled image metadata writing")
                loop.run_until_complete(self.connect_to_kvm(no_delay=True))
            except Exception as err:
                if isinstance(err, MsdError):
                    log = logger.error
                else:
                    log = logger.exception
                log("Mass-storage device is not operational: %s", err)
                self._device_path = ""
        else:
            logger.warning("Mass-storage device is not operational")

    @_msd_operated
    async def connect_to_kvm(self, no_delay: bool=False) -> None:
        with self.__region:
            if self.__device_info:
                raise MsdAlreadyConnectedToKvmError()
            # TODO: disable gpio
            if not no_delay:
                await asyncio.sleep(self.__init_delay)
            await self.__load_device_info()
            get_logger().info("Mass-storage device switched to KVM: %s", self.__device_info)

    @_msd_operated
    async def connect_to_pc(self) -> None:
        with self.__region:
            if not self.__device_info:
                raise MsdAlreadyConnectedToPcError()
            # TODO: enable gpio
            self.__device_info = None
            get_logger().info("Mass-storage device switched to Server")

    def get_state(self) -> Dict:
        info = (self.__saved_device_info._asdict() if self.__saved_device_info else None)
        if info:
            info["hw"] = (info["hw"]._asdict() if info["hw"] else None)
            info["image"] = (info["image"]._asdict() if info["image"] else None)

        connected_to: Optional[str] = None
        if self._device_path:
            connected_to = ("kvm" if self.__device_info else "server")

        return {
            "in_operate": bool(self._device_path),
            "connected_to": connected_to,
            "busy": bool(self.__device_file),
            "written": self.__written,
            "info": info,
        }

    async def cleanup(self) -> None:
        await self.__close_device_file()
        # TODO: disable gpio

    @_msd_operated
    async def __aenter__(self) -> "MassStorageDevice":
        self.__region.enter()
        try:
            if not self.__device_info:
                raise MsdIsNotConnectedToKvmError()
            self.__device_file = await aiofiles.open(self.__device_info.path, mode="w+b", buffering=0)
            self.__written = 0
            return self
        finally:
            self.__region.exit()

    async def write_image_info(self, name: str, complete: bool) -> None:
        assert self.__device_file
        assert self.__device_info
        if self.__write_meta:
            if self.__device_info.size - self.__written > _IMAGE_INFO_SIZE:
                await self.__device_file.seek(self.__device_info.size - _IMAGE_INFO_SIZE)
                await self.__write_to_device_file(_make_image_info_bytes(name, self.__written, complete))
                await self.__device_file.seek(0)
                await self.__load_device_info()
            else:
                get_logger().error("Can't write image info because device is full")

    async def write_image_chunk(self, chunk: bytes) -> int:
        await self.__write_to_device_file(chunk)
        self.__written += len(chunk)
        return self.__written

    async def __aexit__(
        self,
        _exc_type: Type[BaseException],
        _exc: BaseException,
        _tb: types.TracebackType,
    ) -> None:
        try:
            await self.__close_device_file()
        finally:
            self.__region.exit()

    async def __write_to_device_file(self, data: bytes) -> None:
        assert self.__device_file
        await self.__device_file.write(data)
        await self.__device_file.flush()
        await self.__loop.run_in_executor(None, os.fsync, self.__device_file.fileno())

    async def __load_device_info(self) -> None:
        device_info = await self.__loop.run_in_executor(None, _explore_device, self._device_path)
        if not device_info:
            raise MsdError("Can't explore device %r" % (self._device_path))
        self.__device_info = self.__saved_device_info = device_info

    async def __close_device_file(self) -> None:
        try:
            if self.__device_file:
                get_logger().info("Closing mass-storage device file ...")
                await self.__device_file.close()
        except Exception:
            get_logger().exception("Can't close mass-storage device file")
            # TODO: reset device file
        self.__device_file = None
        self.__written = 0