# Copyright (C) 2012-2016 by the Free Software Foundation, Inc.
#
# This file is part of GNU Mailman.
#
# GNU Mailman 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.
#
# GNU Mailman 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
# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.

"""Database factory."""

import os
import types
import alembic.command

from alembic.migration import MigrationContext
from alembic.script import ScriptDirectory
from flufl.lock import Lock
from mailman import public
from mailman.config import config
from mailman.database.alembic import alembic_cfg
from mailman.database.model import Model
from mailman.interfaces.database import (
    DatabaseError, IDatabase, IDatabaseFactory)
from mailman.utilities.modules import call_name
from sqlalchemy import MetaData
from zope.interface import implementer
from zope.interface.verify import verifyObject


LAST_STORM_SCHEMA_VERSION = '20130406000000'


@public
@implementer(IDatabaseFactory)
class DatabaseFactory:
    """Create a new database."""

    @staticmethod
    def create():
        """See `IDatabaseFactory`."""
        with Lock(os.path.join(config.LOCK_DIR, 'dbcreate.lck')):
            database_class = config.database['class']
            database = call_name(database_class)
            verifyObject(IDatabase, database)
            database.initialize()
            SchemaManager(database).setup_database()
            database.commit()
            return database


@public
class SchemaManager:
    "Manage schema migrations."""

    def __init__(self, database):
        self._database = database
        self._script = ScriptDirectory.from_config(alembic_cfg)

    def _get_storm_schema_version(self):
        metadata = MetaData()
        metadata.reflect(bind=self._database.engine)
        if 'version' not in metadata.tables:
            # There are no Storm artifacts left.
            return None
        Version = metadata.tables['version']
        last_version = self._database.store.query(Version.c.version).filter(
            Version.c.component == 'schema'
            ).order_by(Version.c.version.desc()).first()
        # Don't leave open transactions or they will block any schema change.
        self._database.commit()
        return last_version

    def setup_database(self):
        context = MigrationContext.configure(self._database.store.connection())
        current_rev = context.get_current_revision()
        head_rev = self._script.get_current_head()
        if current_rev == head_rev:
            # We're already at the latest revision so there's nothing to do.
            return head_rev
        if current_rev is None:
            # No Alembic information is available.
            storm_version = self._get_storm_schema_version()
            if storm_version is None:
                # Initial database creation.
                Model.metadata.create_all(self._database.engine)
                self._database.commit()
                alembic.command.stamp(alembic_cfg, 'head')
            else:
                # The database was previously managed by Storm.
                if storm_version.version < LAST_STORM_SCHEMA_VERSION:
                    raise DatabaseError(
                        'Upgrades skipping beta versions is not supported.')
                # Run migrations to remove the Storm-specific table and upgrade
                # to SQLAlchemy and Alembic.
                alembic.command.upgrade(alembic_cfg, 'head')
        elif current_rev != head_rev:
            alembic.command.upgrade(alembic_cfg, 'head')
        return head_rev


def _reset(self):
    """See `IDatabase`."""
    # Avoid a circular import at module level.
    from mailman.database.model import Model
    self.store.rollback()
    self._pre_reset(self.store)
    Model._reset(self)
    self._post_reset(self.store)
    self.store.commit()


@public
@implementer(IDatabaseFactory)
class DatabaseTestingFactory:
    """Create a new database for testing."""

    @staticmethod
    def create():
        """See `IDatabaseFactory`."""
        database_class = config.database['class']
        database = call_name(database_class)
        verifyObject(IDatabase, database)
        database.initialize()
        # Remove existing tables (PostgreSQL will keep them across runs)
        metadata = MetaData(bind=database.engine)
        metadata.reflect()
        metadata.drop_all()
        database.commit()
        # Now create the current model without Alembic upgrades.
        Model.metadata.create_all(database.engine)
        database.commit()
        # Make _reset() a bound method of the database instance.
        database._reset = types.MethodType(_reset, database)
        return database