"""

Move a file in the safest way possible::

    >>> from django.core.files.move import file_move_save

    >>> file_move_save("/tmp/old_file", "/tmp/new_file")

"""

import os

from django.core.files import locks

try:

    from shutil import copystat

except ImportError:

    import stat

    def copystat(src, dst):

        """Copy all stat info (mode bits, atime and mtime) from src to dst"""

        st = os.stat(src)

        mode = stat.S_IMODE(st.st_mode)

        if hasattr(os, 'utime'):

            os.utime(dst, (st.st_atime, st.st_mtime))

        if hasattr(os, 'chmod'):

            os.chmod(dst, mode)

__all__ = ['file_move_safe']

def _samefile(src, dst):

    # Macintosh, Unix.

    if hasattr(os.path,'samefile'):

        try:

            return os.path.samefile(src, dst)

        except OSError:

            return False

    # All other platforms: check for same pathname.

    return (os.path.normcase(os.path.abspath(src)) ==

            os.path.normcase(os.path.abspath(dst)))

def file_move_safe(old_file_name, new_file_name, chunk_size = 1024*64, allow_overwrite=False):

    """

    Moves a file from one location to another in the safest way possible.

    First, try using ``shutils.move``, which is OS-dependent but doesn't break

    if moving across filesystems. Then, try ``os.rename``, which will break

    across filesystems. Finally, streams manually from one file to another in

    pure Python.

    If the destination file exists and ``allow_overwrite`` is ``False``, this

    function will throw an ``IOError``.

    """

    # There's no reason to move if we don't have to.

    if _samefile(old_file_name, new_file_name):

        return

    try:

        os.rename(old_file_name, new_file_name)

        return

    except OSError:

        # This will happen with os.rename if moving to another filesystem

        # or when moving opened files on certain operating systems

        pass

    # first open the old file, so that it won't go away

    old_file = open(old_file_name, 'rb')

    try:

        # now open the new file, not forgetting allow_overwrite

        fd = os.open(new_file_name, os.O_WRONLY | os.O_CREAT | getattr(os, 'O_BINARY', 0) |

                                    (not allow_overwrite and os.O_EXCL or 0))

        try:

            locks.lock(fd, locks.LOCK_EX)

            current_chunk = None

            while current_chunk != '':

                current_chunk = old_file.read(chunk_size)

                os.write(fd, current_chunk)

        finally:

            locks.unlock(fd)

            os.close(fd)

    finally:

        old_file.close()

    copystat(old_file_name, new_file_name)

    try:

        os.remove(old_file_name)

    except OSError, e:

        # Certain operating systems (Cygwin and Windows)

        # fail when deleting opened files, ignore it

        if getattr(e, 'winerror', 0) != 32:

            # FIXME: should we also ignore errno 13?

            raise