# -*- coding: utf-8 -*-

##########################################################################
# OpenLP - Open Source Lyrics Projection                                 #
# ---------------------------------------------------------------------- #
# Copyright (c) 2008-2019 OpenLP Developers                              #
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# This program is free software: you can redistribute it and/or modify   #
# it under the terms of the GNU General Public License as published by   #
# the Free Software Foundation, either version 3 of the License, or      #
# (at your option) any later version.                                    #
#                                                                        #
# This program 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 General Public License for more details.                           #
#                                                                        #
# You should have received a copy of the GNU General Public License      #
# along with this program.  If not, see <https://www.gnu.org/licenses/>. #
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"""
The :mod:`db` module provides helper functions for database related methods.
"""
import logging
from copy import deepcopy

import sqlalchemy


log = logging.getLogger(__name__)


def drop_column(op, tablename, columnname):
    drop_columns(op, tablename, [columnname])


def drop_columns(op, tablename, columns):
    """
    Column dropping functionality for SQLite, as there is no DROP COLUMN support in SQLite

    From https://github.com/klugjohannes/alembic-sqlite
    """

    # get the db engine and reflect database tables
    engine = op.get_bind()
    meta = sqlalchemy.MetaData(bind=engine)
    meta.reflect()

    # create a select statement from the old table
    old_table = meta.tables[tablename]
    select = sqlalchemy.sql.select([c for c in old_table.c if c.name not in columns])

    # get remaining columns without table attribute attached
    remaining_columns = [deepcopy(c) for c in old_table.columns if c.name not in columns]
    for column in remaining_columns:
        column.table = None

    # create a temporary new table
    new_tablename = '{0}_new'.format(tablename)
    op.create_table(new_tablename, *remaining_columns)
    meta.reflect()
    new_table = meta.tables[new_tablename]

    # copy data from old table
    insert = sqlalchemy.sql.insert(new_table).from_select([c.name for c in remaining_columns], select)
    engine.execute(insert)

    # drop the old table and rename the new table to take the old tables
    # position
    op.drop_table(tablename)
    op.rename_table(new_tablename, tablename)