"""Windows-specific implementation of process utilities.

This file is only meant to be imported by process.py, not by end-users.
"""

#-----------------------------------------------------------------------------
#  Copyright (C) 2010  The IPython Development Team
#
#  Distributed under the terms of the BSD License.  The full license is in
#  the file COPYING, distributed as part of this software.
#-----------------------------------------------------------------------------

#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------
from __future__ import print_function

# stdlib
import os
import sys

from subprocess import STDOUT

# our own imports
from ._process_common import read_no_interrupt, process_handler

#-----------------------------------------------------------------------------
# Function definitions
#-----------------------------------------------------------------------------

class AvoidUNCPath(object):
    """A context manager to protect command execution from UNC paths.

    In the Win32 API, commands can't be invoked with the cwd being a UNC path.
    This context manager temporarily changes directory to the 'C:' drive on
    entering, and restores the original working directory on exit.

    The context manager returns the starting working directory *if* it made a
    change and None otherwise, so that users can apply the necessary adjustment
    to their system calls in the event of a change.

    Example
    -------
    ::
        cmd = 'dir'
        with AvoidUNCPath() as path:
            if path is not None:
                cmd = '"pushd %s &&"%s' % (path, cmd)
            os.system(cmd)
    """
    def __enter__(self):
        self.path = os.getcwd()
        self.is_unc_path = self.path.startswith(r"\\")
        if self.is_unc_path:
            # change to c drive (as cmd.exe cannot handle UNC addresses)
            os.chdir("C:")
        return self.path

    def __exit__(self, exc_type, exc_value, traceback):
        if self.is_unc_path:
            os.chdir(self.path)


def _find_cmd(cmd):
    """Find the full path to a .bat or .exe using the win32api module."""
    try:
        from win32api import SearchPath
    except ImportError:
        raise ImportError('you need to have pywin32 installed for this to work')
    else:
        PATH = os.environ['PATH']
        extensions = ['.exe', '.com', '.bat', '.py']
        path = None
        for ext in extensions:
            try:
                path = SearchPath(PATH, cmd + ext)[0]
            except:
                pass
        if path is None:
            raise OSError("command %r not found" % cmd)
        else:
            return path


def _system_body(p):
    """Callback for _system."""
    for line in read_no_interrupt(p.stdout).splitlines():
        print(line, file=sys.stdout)
    for line in read_no_interrupt(p.stderr).splitlines():
        print(line, file=sys.stderr)


def system(cmd):
    """Win32 version of os.system() that works with network shares.

    Note that this implementation returns None, as meant for use in IPython.

    Parameters
    ----------
    cmd : str
      A command to be executed in the system shell.

    Returns
    -------
    None : we explicitly do NOT return the subprocess status code, as this
    utility is meant to be used extensively in IPython, where any return value
    would trigger :func:`sys.displayhook` calls.
    """
    with AvoidUNCPath() as path:
        if path is not None:
            cmd = '"pushd %s &&"%s' % (path, cmd)
        process_handler(cmd, _system_body)


def getoutput(cmd):
    """Return standard output of executing cmd in a shell.

    Accepts the same arguments as os.system().

    Parameters
    ----------
    cmd : str
      A command to be executed in the system shell.

    Returns
    -------
    stdout : str
    """

    with AvoidUNCPath() as path:
        if path is not None:
            cmd = '"pushd %s &&"%s' % (path, cmd)
        out = process_handler(cmd, lambda p: p.communicate()[0], STDOUT)

    if out is None:
        out = ''
    return out