import psycopg2
import psycopg2.extensions

import constants
from config import read_db_config
from log_setup import logger


class DBConnectionManager:
    def __init__(self):
        self._conn = None

    def connect(self):
        config = read_db_config()
        logger.debug("Establishing database connection.")
        self._conn = psycopg2.connect("dbname='{}' user='{}' password='{}' host='localhost'".format(
            config.db_name, config.db_user, config.db_pass
        ))
        logger.debug("Established database connection.")

    def get_connection(self) -> psycopg2.extensions.connection:
        """
        Get the database connection.
        If not already connected, this reads the database config file and connects to the DB.
        Otherwise, the already active connection is returned.
        """
        if self._conn is None:
            self.connect()
        return self._conn


# Global instance that will hold our DB connection
conn_manager = DBConnectionManager()


def get_existing_tables():
    conn = conn_manager.get_connection()
    cur = conn.cursor()
    table_names = ", ".join("'{}'".format(tablename) for tablename in constants.DB_TABLE_NAMES)
    cur.execute(
        "SELECT tablename FROM pg_tables WHERE"
        "  schemaname = 'public' AND"
        "  tablename IN ({})".format(
            table_names
        )
    )
    return [table for (table,) in cur.fetchall()]


def init_database(erase: bool = False):
    tables = get_existing_tables()

    if not erase and len(tables) > 0:
        logger.error("Aborting database initialization: Tables {} already exist".format(", ".join(tables)))
        return
    conn = conn_manager.get_connection()
    cur = conn.cursor()

    with open(constants.DATABASE_SCHEMA_PATH, "r") as f:
        cur.execute(f.read())
        conn.commit()
    logger.verbose("Initialized DB tables.")