"""A clean wrapper around Windows APIs allowing interprocess communication over named pipes

Here is a clear, simple explanation of the incantation needed to do this correctly:

* From the client, spawn the server.
* The server should CreateNamedPipe, then ConnectNamedPipe
* The client must poll for the pipe, then open with CreateFile
* Then each can read/write from the pipe as needed.
* Finally, the client should close the pipe.
"""

import io
import time
from types import TracebackType
from typing import Optional, Type
import _winapi
import time
from contextlib import ContextDecorator


class NamedPipeBase(io.StringIO):
    handle = _winapi.NULL
    buffer_size = 2**16

    def __init__(self, name: str) -> None:
        self.name = r'\\.\pipe\{}'.format(name)

    def read(self, size: Optional[int] = None) -> str:
        if self.handle != _winapi.NULL:
            msg, status = _winapi.ReadFile(self.handle, size if size else self.buffer_size)
            return msg.decode()
        else:
            raise WindowsError("Cannot read pipe")

    def write(self, msg: str) -> int:
        if self.handle != _winapi.NULL:
            return _winapi.WriteFile(self.handle, msg.encode(), len(msg))
        else:
            raise WindowsError("Cannot read pipe")

    def __exit__(self,
                 exc_ty: Optional[Type[BaseException]] = None,
                 exc_val: Optional[BaseException] = None,
                 exc_tb: Optional[TracebackType] = None,
                 ) -> bool:
        if self.handle != _winapi.NULL:
            _winapi.CloseHandle(self.handle)
        return False


class NamedPipeServer(NamedPipeBase):
    def __init__(self, name: str) -> None:
        super().__init__(name)
        self.handle = _winapi.CreateNamedPipe(
            self.name,
            _winapi.PIPE_ACCESS_DUPLEX | _winapi.FILE_FLAG_FIRST_PIPE_INSTANCE,
            _winapi.PIPE_READMODE_MESSAGE | _winapi.PIPE_TYPE_MESSAGE | _winapi.PIPE_WAIT,
            1,  # one instance
            self.buffer_size,
            self.buffer_size,
            0,
            _winapi.NULL,
        )
        if _winapi.GetLastError() != 0:
            err = _winapi.GetLastError()
            raise WindowsError(f'Error creating pipe: {err}')

    def __enter__(self) -> 'NamedPipeServer':
        _winapi.ConnectNamedPipe(self.handle, _winapi.NULL)
        return self


class NamedPipeClient(NamedPipeBase):
    def __init__(self, name: str) -> None:
        super().__init__(name)
        # Sadly we need to try several times until this works, or it times out
        # thanks Windows
        done = False
        while not done:
            try:
                self.handle = _winapi.CreateFile(
                    self.name,
                    _winapi.GENERIC_READ | _winapi.GENERIC_WRITE,
                    0,
                    _winapi.NULL,
                    _winapi.OPEN_EXISTING,
                    0,
                    _winapi.NULL,
                )
                _winapi.SetNamedPipeHandleState(self.handle,
                                                _winapi.PIPE_READMODE_MESSAGE,
                                                _winapi.NULL,
                                                _winapi.NULL)
            except FileNotFoundError:
                raise WindowsError(
                        "Unable to open connection to pipe at {}".format(self.name)
                    )
            except WindowsError as e:
                if e.winerror not in (_winapi.ERROR_SEM_TIMEOUT, _winapi.ERROR_PIPE_BUSY):
                    break
                else:
                    time.sleep(1)
            break

    def __enter__(self) -> 'NamedPipeClient':
        return self