"""custom storages for the system source"""

from os import unlink, path as osp

from yams.schema import role_name

from cubicweb import Binary

def set_attribute_storage(repo, etype, attr, storage):

    repo.system_source.set_storage(etype, attr, storage)

def unset_attribute_storage(repo, etype, attr):

    repo.system_source.unset_storage(etype, attr)

class Storage(object):

    """abstract storage

    * If `source_callback` is true (by default), the callback will be run during

      query result process of fetched attribute's valu and should have the

      following prototype::

        callback(self, source, value)

      where `value` is the value actually stored in the backend. None values

      will be skipped (eg callback won't be called).

    * if `source_callback` is false, the callback will be run during sql

      generation when some attribute with a custom storage is accessed and

      should have the following prototype::

        callback(self, generator, relation, linkedvar)

      where `generator` is the sql generator, `relation` the current rql syntax

      tree relation and linkedvar the principal syntax tree variable holding the

      attribute.

    """

    is_source_callback = True

    def callback(self, *args):

        """see docstring for prototype, which vary according to is_source_callback

        """

        raise NotImplementedError()

    def entity_added(self, entity, attr):

        """an entity using this storage for attr has been added"""

        raise NotImplementedError()

    def entity_updated(self, entity, attr):

        """an entity using this storage for attr has been updatded"""

        raise NotImplementedError()

    def entity_deleted(self, entity, attr):

        """an entity using this storage for attr has been deleted"""

        raise NotImplementedError()

# TODO

# * make it configurable without code

# * better file path attribution

# * handle backup/restore

def uniquify_path(dirpath, basename):

    """return a unique file name for `basename` in `dirpath`, or None

    if all attemps failed.

    XXX subject to race condition.

    """

    path = osp.join(dirpath, basename)

    if not osp.isfile(path):

        return path

    base, ext = osp.splitext(path)

    for i in xrange(1, 256):

        path = '%s%s%s' % (base, i, ext)

        if not osp.isfile(path):

            return path

    return None

class BytesFileSystemStorage(Storage):

    """store Bytes attribute value on the file system"""

    def __init__(self, defaultdir, fsencoding='utf-8'):

        self.default_directory = defaultdir

        self.fsencoding = fsencoding

    def callback(self, source, value):

        """sql generator callback when some attribute with a custom storage is

        accessed

        """

        fpath = source.binary_to_str(value)

        try:

            return Binary(file(fpath).read())

        except OSError, ex:

            source.critical("can't open %s: %s", value, ex)

            return None

    def entity_added(self, entity, attr):

        """an entity using this storage for attr has been added"""

        if entity._cw.transaction_data.get('fs_importing'):

            binary = Binary(file(entity[attr].getvalue()).read())

        else:

            binary = entity.pop(attr)

            fpath = self.new_fs_path(entity, attr)

            # bytes storage used to store file's path

            entity[attr] = Binary(fpath)

            file(fpath, 'w').write(binary.getvalue())

        return binary

    def entity_updated(self, entity, attr):

        """an entity using this storage for attr has been updatded"""

        if entity._cw.transaction_data.get('fs_importing'):

            oldpath = self.current_fs_path(entity, attr)

            fpath = entity[attr].getvalue()

            if oldpath != fpath:

            binary = Binary(file(fpath).read())

        else:

            binary = entity.pop(attr)

            fpath = self.current_fs_path(entity, attr)

            UpdateFileOp(entity._cw, filepath=fpath, filedata=binary.getvalue())

        return binary

    def entity_deleted(self, entity, attr):

        """an entity using this storage for attr has been deleted"""

    def new_fs_path(self, entity, attr):

        # We try to get some hint about how to name the file using attribute's

        # name metadata, so we use the real file name and extension when

        # available. Keeping the extension is useful for example in the case of

        # PIL processing that use filename extension to detect content-type, as

        # well as providing more understandable file names on the fs.

        basename = [str(entity.eid), attr]

        name = entity.attr_metadata(attr, 'name')

        if name is not None:

            basename.append(name.encode(self.fsencoding))

        fspath = uniquify_path(self.default_directory, '_'.join(basename))

        if fspath is None:

            msg = entity._cw._('failed to uniquify path (%s, %s)') % (

                dirpath, '_'.join(basename))

            raise ValidationError(entity.eid, {role_name(attr, 'subject'): msg})

        return fspath

    def current_fs_path(self, entity, attr):

        sysource = entity._cw.pool.source('system')

        cu = sysource.doexec(entity._cw,

                             'SELECT cw_%s FROM cw_%s WHERE cw_eid=%s' % (

                             attr, entity.__regid__, entity.eid))

        rawvalue = cu.fetchone()[0]

        if rawvalue is None: # no previous value

            return self.new_fs_path(entity, attr)

        return sysource._process_value(rawvalue, cu.description[0],

                                       binarywrap=str)

    def rollback_event(self):

    def commit_event(self):

    def precommit_event(self):

        try:

            file(self.filepath, 'w').write(self.filedata)

        except Exception, ex:

            self.exception(str(ex))