#  ___________________________________________________________________________
#
#  Pyomo: Python Optimization Modeling Objects
#  Copyright 2017 National Technology and Engineering Solutions of Sandia, LLC
#  Under the terms of Contract DE-NA0003525 with National Technology and
#  Engineering Solutions of Sandia, LLC, the U.S. Government retains certain
#  rights in this software.
#  This software is distributed under the 3-clause BSD License.
#  ___________________________________________________________________________

import ctypes
import multiprocessing
import os

def _as_bytes(val):
    """Helper function to coerce a string to a bytes() object"""
    if isinstance(val, bytes):
        return val
    elif val is not None:
        return val.encode('utf-8')
    return None


def _as_unicode(val):
    """Helper function to coerce a string to a unicode() object"""
    if isinstance(val, str):
        return val
    elif val is not None:
        return val.decode()
    return None


def _attempt_ctypes_cdll(name):
    """Load a CDLL library, returning bool indicating success"""
    try:
        dll = ctypes.CDLL(name)
        return True
    except OSError:
        return False


def _load_dll(name, timeout=10):
    """Load a DLL with a timeout

    On some platforms and some DLLs (notably Windows GitHub Actions with
    Python 3.5, 3.6, and 3.7 and the msvcr90.dll) we have observed
    behavior where the ctypes.CDLL() call hangs indefinitely. This uses
    multiprocessing to attempt the import in a subprocess (with a
    timeout) and then only calls the import in the main process if the
    subprocess succeeded.

    Performance note: CtypesEnviron only ever attempts to load a DLL
    once (the DLL reference is then held in a class attribute), and this
    interface only spawns the subprocess if ctypes.util.find_library
    actually locates the target library. This will have a measurable
    impact on Windows (where the DLLs exist), but not on other platforms.

    The default timeout of 10 is arbitrary. For simple situations, 1
    seems adequate. However, more complex examples have been observed
    that needed timeout==5. Using a default of 10 is simply doubling
    that observed case.

    """
    if not ctypes.util.find_library(name):
        return False, None
    if _load_dll.pool is None:
        _load_dll.pool = multiprocessing.Pool(1)
    job = _load_dll.pool.apply_async(_attempt_ctypes_cdll, (name,))
    try:
        result = job.get(timeout)
    except multiprocessing.TimeoutError:
        result = False
        # If there was a timeout, then the subprocess is likely hung and
        # cannot be reused.  Terminate it here (subsequent calls will
        # create a new Pool)
        _load_dll.pool.terminate()
        _load_dll.pool = None
    if result:
        return result, ctypes.CDLL(name)
    else:
        return result, None

# For efficiency, cache the multiprocessing Pool between calls to _load_dll
_load_dll.pool = None


class _RestorableEnvironInterface(object):
    """Interface to track environment changes and restore state"""

    def __init__(self, dll):
        assert dll.available()
        self.dll = dll
        self._original_state = {}

        # Transfer over the current os.environ
        for key, val in list(os.environ.items()):
            if val != self[key]:
                self[key] = val

        # If we can get a dictionary of the current environment (not
        # always possible), then remove any keys that are not in
        # os.environ
        origEnv = self.dll.get_env_dict()
        if origEnv is not None:
            for key in origEnv:
                if key not in os.environ:
                    del self[key]

    def restore(self):
        for key, val in self._original_state.items():
            if not val:
                if self[key] is not None:
                    del self[key]
            else:
                self[key] = val
        self._original_state = {}

    def __getitem__(self, key):
        if isinstance(key, str):
            return self.dll.wgetenv(key)
        else:
            return self.dll.getenv(key)

    def __setitem__(self, key, val):
        if key not in self._original_state:
            self._original_state[key] = self[key]

        if isinstance(key, str):
            if isinstance(val, str):
                self.dll.wputenv_s(key, val)
            else:
                self.dll.wputenv_s(key, _as_unicode(val))
        elif isinstance(val, str):
            self.dll.wputenv_s(_as_unicode(key), val)
        else:
            self.dll.putenv_s(key, val)

    def __delitem__(self, key):
        if key not in self._original_state:
            self._original_state[key] = self[key]

        if isinstance(key, str):
            self.dll.wputenv_s(key, u'')
        else:
            self.dll.putenv_s(key, b'')


class _OSEnviron(object):
    """Helper class to proxy a "DLL-like" interface to os.environ"""

    _libname = 'os.environ'

    def available(self):
        return True

    def get_env_dict(self):
        return dict(os.environ)

    def getenv(self, key):
        # environb is not always present and depends on how the
        # interpreter was compiled.  Fall back on casting environ if
        # it is not available.
        try:
            return os.environb.get(key, None)
        except AttributeError:
            return _as_bytes(os.environ.get(_as_unicode(key),None))

    def wgetenv(self, key):
        # PY2 doesn't distinguish, and PY3's environ is nominally
        # unicode.  We will coerce the result to unicode to guarantee
        # the result type.
        return _as_unicode(os.environ.get(key, None))

    def putenv_s(self, key, val):
        # Win32 convention deletes environ entries when the string is empty
        if not val:
            if key in os.environ:
                del os.environ[key]
            return

        os.environb[key] = val

    def wputenv_s(self, key, val):
        # Win32 convention deletes environ entries when the string is empty
        if not val:
            if key in os.environ:
                del os.environ[key]
            return

        os.environ[key] = val


class _MsvcrtDLL(object):
    """Helper class to manage the interface with the MSVCRT runtime"""

    def __init__(self, name):
        self._libname = name
        if name is None:
            self._loaded = False
        else:
            self._loaded = None
        self.dll = None

    def available(self):
        if self._loaded is not None:
            return self._loaded

        self._loaded,  self.dll = _load_dll(self._libname)
        if not self._loaded:
            return self._loaded

        self.putenv_s = self.dll._putenv_s
        self.putenv_s.argtypes = [ctypes.c_char_p, ctypes.c_char_p]
        self.putenv_s.restype = ctypes.c_int

        self.wputenv_s = self.dll._wputenv_s
        self.wputenv_s.argtypes = [ctypes.c_wchar_p, ctypes.c_wchar_p]
        self.wputenv_s.restype = ctypes.c_int

        self.getenv = self.dll.getenv
        self.getenv.argtypes = [ctypes.c_char_p]
        self.getenv.restype = ctypes.c_char_p

        self.wgetenv = self.dll._wgetenv
        self.wgetenv.argtypes = [ctypes.c_wchar_p]
        self.wgetenv.restype = ctypes.c_wchar_p

        return self._loaded

    def get_env_dict(self):
        if not self.available():
            return None

        try:
            envp = ctypes.POINTER(ctypes.c_wchar_p).in_dll(
                self.dll, '_wenviron')
            if not envp.contents:
                envp = None
        except ValueError:
            envp = None
        if envp is None:
            try:
                envp = ctypes.POINTER(ctypes.c_char_p).in_dll(
                    self.dll, '_environ')
                if not envp.contents:
                    return None
            except ValueError:
                return None

        ans = {}
        size = 0
        for line in envp:
            if not line:
                break
            size += len(line)
            if len(line) == 0:
                raise ValueError(
                    "Error processing MSVCRT _environ: "
                    "0-length string encountered")
            if size > 32767:
                raise ValueError(
                    "Error processing MSVCRT _environ: "
                    "exceeded max environment block size (32767)")
            key, val = line.split('=', 1)
            ans[key] = val
        return ans


class _Win32DLL(object):
    """Helper class to manage the interface with the Win32 runtime"""

    def __init__(self, name):
        self._libname = name
        if name is None:
            self._loaded = False
        else:
            self._loaded = None
        self.dll = None

    def available(self):
        if self._loaded is not None:
            return self._loaded

        self._loaded,  self.dll = _load_dll(self._libname)
        if not self._loaded:
            return self._loaded

        self.putenv_s = self.dll.SetEnvironmentVariableA
        self.putenv_s.argtypes = [ctypes.c_char_p, ctypes.c_char_p]
        self.putenv_s.restype = ctypes.c_bool

        self.wputenv_s = self.dll.SetEnvironmentVariableW
        self.wputenv_s.argtypes = [ctypes.c_wchar_p, ctypes.c_wchar_p]
        self.wputenv_s.restype = ctypes.c_bool

        # Note DWORD == c_ulong
        self._getenv_dll = self.dll.GetEnvironmentVariableA
        self._getenv_dll.argtypes = [
            ctypes.c_char_p, ctypes.c_char_p, ctypes.c_ulong]
        self._getenv_dll.restype = ctypes.c_ulong

        self._wgetenv_dll = self.dll.GetEnvironmentVariableW
        self._wgetenv_dll.argtypes = [
            ctypes.c_wchar_p, ctypes.c_wchar_p, ctypes.c_ulong]
        self._wgetenv_dll.restype = ctypes.c_ulong

        # We (arbitrarily) choose to return the unicode environ
        self._envstr = self.dll.GetEnvironmentStringsW
        self._envstr.argtypes = []
        self._envstr.restype = ctypes.POINTER(ctypes.c_wchar)
        self._free_envstr = self.dll.FreeEnvironmentStringsW
        self._free_envstr.argtypes = [ctypes.POINTER(ctypes.c_wchar)]
        self._free_envstr.restype = ctypes.c_bool

        return self._loaded

    def getenv(self, key):
        size = self._getenv_dll(key, None, 0)
        if not size:
            return None
        buf = ctypes.create_string_buffer(b'\0' * size)
        self._getenv_dll(key, buf, size)
        return buf.value or None

    def wgetenv(self, key):
        size = self._wgetenv_dll(key, None, 0)
        if not size:
            return None
        buf = ctypes.create_unicode_buffer(u'\0' * size)
        self._wgetenv_dll(key, buf, size)
        return buf.value or None

    def get_env_dict(self):
        ans = {}
        _str_buf = self._envstr()
        # I am sure there is an easier way to parse this.
        # GetEnvironmentStringsW returns a single const char* that
        # points to a block of memory that contains the environment
        # strings.  Each environment string is NULL terminated, and an
        # empty string (effectively two consecutive NULLs) indicates the
        # end of the block.  The following just parses that data
        # character by character to reconstitute the original
        # environment strings.
        _null = {u'\0', b'\0'}
        i = 0
        while _str_buf[i] not in _null:
            _str = ''
            while _str_buf[i] not in _null:
                _str += _str_buf[i]
                i += len(_str_buf[i])
                if len(_str_buf[i]) == 0:
                    raise ValueError(
                        "Error processing Win32 GetEnvironmentStringsW: "
                        "0-length character encountered")
                if i > 32767: # max var length
                    raise ValueError(
                        "Error processing Win32 GetEnvironmentStringsW: "
                        "exceeded max environment block size (32767)")
            key, val = _str.split('=', 1)
            ans[key] = val
            i += len(_str_buf[i]) # Skip the NULL
        self._free_envstr(_str_buf)
        return ans


class CtypesEnviron(object):
    """A context manager for managing environment variables

    This class provides a simplified interface for consistently setting
    and restoring environment variables, with special handling to ensure
    consistency with the C Runtime Library environment on Windows
    platforms.

    `os.environ` reflects the current python environment variables, and
    will be passed to subprocesses.  However, it does not reflect the C
    Runtime Library (MSVCRT) environment on Windows platforms.  This can
    be problemmatic as DLLs loaded through the CTYPES interface will see
    the MSVCRT environment and not os.environ.  This class provides a
    way to manage environment variables and pass changes to both
    os.environ and the MSVCRT runtime.

    This class implements a context manager API, so that clients can
    temporarily change - and then subsequently restore - the
    environment.

    .. testcode::
       :hide:

       import os
       from pyomo.common.env import TemporaryEnv
       orig_env_val = os.environ.get('TEMP_ENV_VAR', None)

    .. doctest::

       >>> os.environ['TEMP_ENV_VAR'] = 'original value'
       >>> print(os.environ['TEMP_ENV_VAR'])
       original value

       >>> with CtypesEnviron(TEMP_ENV_VAR='temporary value'):
       ...    print(os.envion['TEMP_ENV_VAR'])
       temporary value

       >>> print(os.environ['TEMP_ENV_VAR'])
       original value

    .. testcode::
       :hide:

       if orig_env_val is None:
           del os.environ['TEMP_ENV_VAR']
       else:
           os.environ['TEMP_ENV_VAR'] = orig_env_val

    """

    # Windows has a number of C Runtime Libraries, each of which can
    # hold its own independent copy of the system environment
    #
    # Note that this order is important: kernel32 appears to track
    # os.envion (and it is possible that it could be omitted).  It is
    # important to deal with it before the msvcrt libraries.
    DLLs = [
        _Win32DLL('kernel32'),
        _MsvcrtDLL(getattr(ctypes.util,'find_msvcrt',lambda: None)()),
        _MsvcrtDLL('api-ms-win-crt-environment-l1-1-0'),
        _MsvcrtDLL('msvcrt'),
        _MsvcrtDLL('msvcr120'),
        _MsvcrtDLL('msvcr110'),
        _MsvcrtDLL('msvcr100'),
        _MsvcrtDLL('msvcr90'),
        _MsvcrtDLL('msvcr80'),
        _MsvcrtDLL('msvcr71'),
        _MsvcrtDLL('msvcr70'),
    ]

    def __init__(self, **kwds):
        self.interfaces = [
            _RestorableEnvironInterface(_OSEnviron()),
        ]
        self.interfaces.extend(_RestorableEnvironInterface(dll)
                               for dll in self.DLLs if dll.available())
        # If this is the first time a CtypesEnviron was created, the
        # calls to dll.activate() may have spawned a multiprocessing
        # pool, which we should clean up.
        if _load_dll.pool is not None:
             _load_dll.pool.terminate()
             _load_dll.pool = None
        # Set the incoming env strings on all interfaces...
        for k, v in kwds.items():
            self[k] = v

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, exc_traceback):
        self.restore()

    def restore(self):
        """Restore the environment to the original state

        This restores all environment variables modified through this
        object to the state they were in before this instance made any
        changes.  Note that any changes made directly to os.environ
        outside this instance will not be detected / undone.

        """
        # It is possible that os.environ and the MSVCRT did not start
        # off in sync; e.g., if someone had set a value in os.environ
        # directly.  We will be especially careful and restore each
        # environ back to its original state.  Note that there are cases
        # where some of the libs refer to the same DLL space, so we will
        # restore them in the opposite order that we set them, so that
        # cases where multiple libs point to the same environment things
        # are all restored correctly.
        for lib in reversed(self.interfaces):
            lib.restore()

    def __getitem__(self, key):
        """Return the current environment variable value from os.environ"""
        return os.environ[key]

    def __contains__(self, key):
        """Return True if the key is in os.environ"""
        return key in os.environ

    def __setitem__(self, key, val):
        """Set an environment variable in all known runtime environments"""
        for lib in self.interfaces:
            lib[key] = val

    def __delitem__(self, key):
        """Remove an environment variable from all known runtime environments"""
        for lib in self.interfaces:
            del lib[key]
