import os, stat
import ctypes, ctypes.util
##from ctypes_configure import configure
##from ctypes_configure.cbuild import ExternalCompilationInfo

_libc_name = ctypes.util.find_library('c')
_c_lib = ctypes.cdll.LoadLibrary(_libc_name)

_openat = _c_lib.openat
_openat.argtypes = [ctypes.c_int, ctypes.c_char_p, ctypes.c_int, ctypes.c_int]
_openat.restype = ctypes.c_int

##class _CConfig:
##    _compilation_info_ = ExternalCompilationInfo(
##        pre_include_lines = ['#define _ATFILE_SOURCE'],
##        includes = ['sys/types.h',
##                    'fcntl.h',
##                    'sys/stat.h',
##                    'unistd.h'])
##    struct_stat = configure.Struct("struct stat",
##                                   [("st_dev", ctypes.c_int),
##                                    ("st_ino", ctypes.c_int)])

##    AT_SYMLINK_NOFOLLOW = configure.ConstantInteger('AT_SYMLINK_NOFOLLOW')

##_cConfig = configure.configure(_CConfig)
##_struct_stat = _cConfig['struct_stat']
##_AT_SYMLINK_NOFOLLOW = _cConfig['AT_SYMLINK_NOFOLLOW']

##_fstatat = _c_lib.__fxstatat
##_fstatat.argtypes = [ctypes.c_int, ctypes.c_char_p,
##                     ctypes.POINTER(_struct_stat), ctypes.c_int]
##_fstatat.restype = ctypes.c_int

DEFAULT_FLAGS = (os.O_RDONLY |
                 os.O_LARGEFILE |
                 os.O_NOCTTY |
                 os.O_NONBLOCK)

def openat(fd, name, flags=DEFAULT_FLAGS, mode=0):
    fd = _openat(fd, name, flags, mode)
    if fd < 0:
        raise OSError
    return fd


class DirAt(object):
    __os_close = os.close

    def __init__(self, fd):
        self.fd = fd

    def __del__(self):
        self.__os_close(self.fd)

    def join(self, relpath):
        fd = openat(self.fd, relpath)
        return DirAt(fd)

    def parentdir(self):
        return self.join('..')

    def listdir(self):
        # XXX hack
        return os.listdir('/proc/self/fd/%d' % self.fd)

    def _key(self):
        st = os.fstat(self.fd)
        return (st.st_ino, st.st_dev)

    def __eq__(self, other):
        if not isinstance(other, DirAt):
            return NotImplemented
        return self._key() == other._key()

    def __ne__(self, other):
        if not isinstance(other, DirAt):
            return NotImplemented
        return self._key() != other._key()

    def __hash__(self):
        return hash(self._key())

    def __repr__(self):
        try:
            s = repr(str(self))
        except OSError:
            s = '???'
        return '<DirAt %s>' % (s,)

    def __str__(self):
        parent = self.parentdir()
        if parent == self:
            return '/'
        st1 = os.fstat(self.fd)
        for name in parent.listdir():
            # XXX hack
            try:
                st2 = os.lstat('/proc/self/fd/%d/%s' % (parent.fd, name))
            except OSError:
                continue
            if os.path.samestat(st1, st2):
                return os.path.join(str(parent), name)
        else:
            raise OSError("directory not found in its parent")


def opendir(dir):
    fd = os.open(dir + '/', DEFAULT_FLAGS)
    return DirAt(fd)

def opencwd():
    return opendir('.')