# CodeQ: an online programming tutor.
# Copyright (C) 2015 UL FRI
#
# This program is free software: you can redistribute it and/or modify it under
# the terms of the GNU Affero 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 Affero General Public License for more
# details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.

import os
import threading
import psycopg2

__all__ = ['get_connection', 'return_connection', 'setup', 'models']

_module_access_lock = threading.Lock()

_host = None  # the database hostname/IP
_port = None  # the database port number
_database = None  # the name of the database
_username = None  # the username to access the database
_password = None  # the password to access the database


# database parameters setup

def _get_port():
    try:
        return int(os.environ.get('CODEQ_DB_PORT'))
    except:
        return 5432


def setup(
        host=os.environ.get('CODEQ_DB_HOST') or 'localhost',
        port=_get_port(),
        database=os.environ.get('CODEQ_DB_DATABASE') or 'codeq',
        username=os.environ.get('CODEQ_DB_USER') or 'codeq',
        password=os.environ.get('CODEQ_DB_PASS') or 'c0d3q'
):
    """Sets the database location and authentication parameters."""
    global _host, _port, _database, _username, _password
    _host = host
    _port = port
    _database = database
    _username = username
    _password = password

# connection pooling

_connection_pool = []


def get_connection():
    """Retrieves a database connection from the connection pool."""
    with _module_access_lock:
        if _host is None:
            setup()  # lazy init
        if len(_connection_pool) > 0:
            return _connection_pool.pop()
    return psycopg2.connect(host=_host, port=_port, database=_database, user=_username, password=_password)


def return_connection(connection):
    """Returns the given database connection to the pool."""
    try:
        connection.rollback()  # sanity check
    except:
        return
    with _module_access_lock:
        _connection_pool.append(connection)


if __name__ == '__main__':
    setup()