# Copyright 2012 New Dream Network, LLC (DreamHost)
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

import contextlib
import functools

import alembic
from alembic import context
from alembic import op
import sqlalchemy as sa
from sqlalchemy.engine import reflection

# Neutron milestones for upgrade aliases
LIBERTY = 'liberty'

NEUTRON_MILESTONES = [
    # earlier milestones were not tagged
    LIBERTY,
]

CREATION_OPERATIONS = (sa.sql.ddl.CreateIndex,
                       sa.sql.ddl.CreateTable,
                       sa.sql.ddl.CreateColumn,
                       )
DROP_OPERATIONS = (sa.sql.ddl.DropConstraint,
                   sa.sql.ddl.DropIndex,
                   sa.sql.ddl.DropTable,
                   alembic.ddl.base.DropColumn)


def skip_if_offline(func):
    """Decorator for skipping migrations in offline mode."""
    @functools.wraps(func)
    def decorator(*args, **kwargs):
        if context.is_offline_mode():
            return
        return func(*args, **kwargs)

    return decorator


def raise_if_offline(func):
    """Decorator for raising if a function is called in offline mode."""
    @functools.wraps(func)
    def decorator(*args, **kwargs):
        if context.is_offline_mode():
            raise RuntimeError(_("%s cannot be called while in offline mode") %
                               func.__name__)
        return func(*args, **kwargs)

    return decorator


@raise_if_offline
def schema_has_table(table_name):
    """Check whether the specified table exists in the current schema.

    This method cannot be executed in offline mode.
    """
    bind = op.get_bind()
    insp = sa.engine.reflection.Inspector.from_engine(bind)
    return table_name in insp.get_table_names()


@raise_if_offline
def schema_has_column(table_name, column_name):
    """Check whether the specified column exists in the current schema.

    This method cannot be executed in offline mode.
    """
    bind = op.get_bind()
    insp = sa.engine.reflection.Inspector.from_engine(bind)
    # first check that the table exists
    if not schema_has_table(table_name):
        return
    # check whether column_name exists in table columns
    return column_name in [column['name'] for column in
                           insp.get_columns(table_name)]


@raise_if_offline
def alter_column_if_exists(table_name, column_name, **kwargs):
    """Alter a column only if it exists in the schema."""
    if schema_has_column(table_name, column_name):
        op.alter_column(table_name, column_name, **kwargs)


@raise_if_offline
def drop_table_if_exists(table_name):
    if schema_has_table(table_name):
        op.drop_table(table_name)


@raise_if_offline
def rename_table_if_exists(old_table_name, new_table_name):
    if schema_has_table(old_table_name):
        op.rename_table(old_table_name, new_table_name)


def alter_enum(table, column, enum_type, nullable):
    bind = op.get_bind()
    engine = bind.engine
    if engine.name == 'postgresql':
        values = {'table': table,
                  'column': column,
                  'name': enum_type.name}
        op.execute("ALTER TYPE %(name)s RENAME TO old_%(name)s" % values)
        enum_type.create(bind, checkfirst=False)
        op.execute("ALTER TABLE %(table)s RENAME COLUMN %(column)s TO "
                   "old_%(column)s" % values)
        op.add_column(table, sa.Column(column, enum_type, nullable=nullable))
        op.execute("UPDATE %(table)s SET %(column)s = "
                   "old_%(column)s::text::%(name)s" % values)
        op.execute("ALTER TABLE %(table)s DROP COLUMN old_%(column)s" % values)
        op.execute("DROP TYPE old_%(name)s" % values)
    else:
        op.alter_column(table, column, type_=enum_type,
                        existing_nullable=nullable)


def create_table_if_not_exist_psql(table_name, values):
    if op.get_bind().engine.dialect.server_version_info < (9, 1, 0):
        op.execute("CREATE LANGUAGE plpgsql")
    op.execute("CREATE OR REPLACE FUNCTION execute(TEXT) RETURNS VOID AS $$"
               "BEGIN EXECUTE $1; END;"
               "$$ LANGUAGE plpgsql STRICT;")
    op.execute("CREATE OR REPLACE FUNCTION table_exist(TEXT) RETURNS bool as "
               "$$ SELECT exists(select 1 from pg_class where relname=$1);"
               "$$ language sql STRICT;")
    op.execute("SELECT execute($$CREATE TABLE %(name)s %(columns)s $$) "
               "WHERE NOT table_exist(%(name)r);" %
               {'name': table_name,
                'columns': values})


def remove_foreign_keys(table, foreign_keys):
    for fk in foreign_keys:
        op.drop_constraint(
            constraint_name=fk['name'],
            table_name=table,
            type_='foreignkey'
        )


def create_foreign_keys(table, foreign_keys):
    for fk in foreign_keys:
        op.create_foreign_key(
            constraint_name=fk['name'],
            source_table=table,
            referent_table=fk['referred_table'],
            local_cols=fk['constrained_columns'],
            remote_cols=fk['referred_columns'],
            ondelete='CASCADE'
        )


@contextlib.contextmanager
def remove_fks_from_table(table):
    try:
        inspector = reflection.Inspector.from_engine(op.get_bind())
        foreign_keys = inspector.get_foreign_keys(table)
        remove_foreign_keys(table, foreign_keys)
        yield
    finally:
        create_foreign_keys(table, foreign_keys)
