# copyright 2003-2013 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
#
# This file is part of CubicWeb.
#
# CubicWeb is free software: you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free
# Software Foundation, either version 2.1 of the License, or (at your option)
# any later version.
#
# CubicWeb is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License along
# with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.
"""custom storages for the system source"""

import os
import sys
from os import unlink, path as osp
from contextlib import contextmanager
import tempfile

from logilab.common import nullobject

from yams.schema import role_name

from cubicweb import Binary, ValidationError
from cubicweb.server import hook
from cubicweb.server.edition import EditedEntity


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 value and should have the
      following prototype::

        callback(self, source, cnx, 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()
    def migrate_entity(self, entity, attribute):
        """migrate an entity attribute to the storage"""
        raise NotImplementedError()

# TODO
# * make it configurable without code
# * better file path attribution
# * handle backup/restore

def uniquify_path(dirpath, basename):
    """return a file descriptor and unique file name for `basename` in `dirpath`
    """
    path = basename.replace(osp.sep, '-')
    base, ext = osp.splitext(path)
    return tempfile.mkstemp(prefix=base, suffix=ext, dir=dirpath)

@contextmanager
def fsimport(cnx):
    present = 'fs_importing' in cnx.transaction_data
    old_value = cnx.transaction_data.get('fs_importing')
    cnx.transaction_data['fs_importing'] = True
    yield
    if present:
        cnx.transaction_data['fs_importing'] = old_value
    else:
        del cnx.transaction_data['fs_importing']


_marker = nullobject()


class BytesFileSystemStorage(Storage):
    """store Bytes attribute value on the file system"""
    def __init__(self, defaultdir, fsencoding=_marker, wmode=0o444):
        if fsencoding is not _marker:
            raise ValueError('fsencoding is no longer supported in python 3')
        self.default_directory = defaultdir
        # extra umask to use when creating file
        # 0444 as in "only allow read bit in permission"
        self._wmode = wmode

    def _writecontent(self, fd, binary):
        """write the content of a binary in readonly file

        As the bfss never alters an existing file it does not prevent it from
        working as intended. This is a better safe than sorry approach.
        """
        os.fchmod(fd, self._wmode)
        fileobj = os.fdopen(fd, 'wb')
        binary.to_file(fileobj)
        fileobj.close()


    def callback(self, source, cnx, value):
        """sql generator callback when some attribute with a custom storage is
        accessed
        """
        fpath = source.binary_to_str(value)
        try:
            return Binary.from_file(fpath)
        except EnvironmentError as 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.from_file(entity.cw_edited[attr].getvalue())
            entity._cw_dont_cache_attribute(attr, repo_side=True)
        else:
            binary = entity.cw_edited.pop(attr)
            if binary is not None:
                fd, fpath = self.new_fs_path(entity, attr)
                # bytes storage used to store file's path
                binary_obj = Binary(fpath.encode('utf-8'))
                entity.cw_edited.edited_attribute(attr, binary_obj)
                self._writecontent(fd, binary)
                AddFileOp.get_instance(entity._cw).add_data(fpath)
        return binary

    def entity_updated(self, entity, attr):
        """an entity using this storage for attr has been updated"""
        # get the name of the previous file containing the value
        oldpath = self.current_fs_path(entity, attr)
        if entity._cw.transaction_data.get('fs_importing'):
            # If we are importing from the filesystem, the file already exists.
            # We do not need to create it but we need to fetch the content of
            # the file as the actual content of the attribute
            fpath = entity.cw_edited[attr].getvalue()
            entity._cw_dont_cache_attribute(attr, repo_side=True)
            assert fpath is not None
            binary = Binary.from_file(fpath)
        else:
            # We must store the content of the attributes
            # into a file to stay consistent with the behaviour of entity_add.
            # Moreover, the BytesFileSystemStorage expects to be able to
            # retrieve the current value of the attribute at anytime by reading
            # the file on disk. To be able to rollback things, use a new file
            # and keep the old one that will be removed on commit if everything
            # went ok.
            #
            # fetch the current attribute value in memory
            binary = entity.cw_edited.pop(attr)
            if binary is None:
                fpath = None
            else:
                # Get filename for it
                fd, fpath = self.new_fs_path(entity, attr)
                # write attribute value on disk
                self._writecontent(fd, binary)
                # Mark the new file as added during the transaction.
                # The file will be removed on rollback
                AddFileOp.get_instance(entity._cw).add_data(fpath)
            # reinstall poped value
            if fpath is None:
                entity.cw_edited.edited_attribute(attr, None)
            else:
                # register the new location for the file.
                binary_obj = Binary(fpath.encode('utf-8'))
                entity.cw_edited.edited_attribute(attr, binary_obj)
        if oldpath is not None and oldpath != fpath:
            # Mark the old file as useless so the file will be removed at
            # commit.
            DeleteFileOp.get_instance(entity._cw).add_data(oldpath)
        return binary

    def entity_deleted(self, entity, attr):
        """an entity using this storage for attr has been deleted"""
        fpath = self.current_fs_path(entity, attr)
        if fpath is not None:
            DeleteFileOp.get_instance(entity._cw).add_data(fpath)

    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.cw_attr_metadata(attr, 'name')
        if name is not None:
            basename.append(name)
        fd, fspath = uniquify_path(self.default_directory,
                               '_'.join(basename))
        if fspath is None:
            msg = entity._cw._('failed to uniquify path (%s, %s)') % (
                self.default_directory, '_'.join(basename))
            raise ValidationError(entity.eid, {role_name(attr, 'subject'): msg})
        assert isinstance(fspath, str)
        return fd, fspath

    def current_fs_path(self, entity, attr):
        """return the current fs_path of the attribute, or None is the attr is
        not stored yet.
        """
        sysource = entity._cw.repo.system_source
        cu = sysource.doexec(entity._cw,
                             'SELECT cw_%s FROM cw_%s WHERE cw_eid=%s' % (
                             attr, entity.cw_etype, entity.eid))
        rawvalue = cu.fetchone()[0]
        if rawvalue is None: # no previous value
            return None
        fspath = sysource._process_value(rawvalue, cu.description[0],
                                         binarywrap=bytes)
        return fspath.decode('utf-8')

    def migrate_entity(self, entity, attribute):
        """migrate an entity attribute to the storage"""
        entity.cw_edited = EditedEntity(entity, **entity.cw_attr_cache)
        binary = self.entity_added(entity, attribute)
        if binary is not None:
            cnx = entity._cw
            source = cnx.repo.system_source
            attrs = source.preprocess_entity(entity)
            sql = source.sqlgen.update('cw_' + entity.cw_etype, attrs,
                                       ['cw_eid'])
            source.doexec(cnx, sql, attrs)
        entity.cw_edited = None


class AddFileOp(hook.DataOperationMixIn, hook.Operation):
    def rollback_event(self):
        for filepath in self.get_data():
            assert isinstance(filepath, str)
            try:
                unlink(filepath)
            except Exception as ex:
                self.error("can't remove %s: %s" % (filepath, ex))

class DeleteFileOp(hook.DataOperationMixIn, hook.Operation):
    def postcommit_event(self):
        for filepath in self.get_data():
            assert isinstance(filepath, str)
            try:
                unlink(filepath)
            except Exception as ex:
                self.error("can't remove %s: %s" % (filepath, ex))