"""This module contains functionality for interacting with a PostgreSQL database. It will automatically handle error
conditions (i.e. missing columns) without terminating the entire program. Use the :py:class:`DBConnector` class to
handle database interactions, either as a standalone object or in a context manager."""
import os
import psycopg2
from psycopg2 import DatabaseError

DB_ADDRESS = os.getenv('DB_ADDRESS', 'localhost')
DB_PORT = os.getenv('DB_PORT', 5432)
DB_USER = os.getenv('DB_USER', 'postgres')
DB_PASSWORD = os.getenv('DB_PASSWORD', '')
DB_NAME = os.getenv('DB_NAME', 'postgres')
DB_TABLE = os.getenv('DB_TABLE', 'cables')


class DBConnector:
    """Context managed database class. Use with statements to automatically open and close the database connection, like
    so:

    .. code-block:: python
       with DBConnector() as db:
           db.read()
    """
    def _db_start(self):
        try:
            self.conn = psycopg2.connect(
                f"host={DB_ADDRESS} port={DB_PORT} dbname={DB_NAME} user={DB_USER} password={DB_PASSWORD}")
            self.cur = self.conn.cursor()
        except DatabaseError as e:


    def _db_stop(self):
        self.cur.close()
        self.conn.close()

    def __init__(self):
        self._db_start()

    def __del__(self):
        self._db_stop()

    def __enter__(self):
        self._db_start()

    def __exit__(self):
        self._db_stop()

    def _query(self, sql):
        try:
            self.cur.execute(sql)
            result = self.cur.fetchall()
        except DatabaseError as e:
            print(f"DB ERROR [{e.pgcode}]: {e.pgerror}")
            result = []
        return result

    def read(self, **kwargs):
        """Read rows from a database that match the specified filters.

        :param kwargs: Column constraints; i.e. what value to filter by in what column.
        :returns: A list of dictionaries of all matching rows, or an empty list if no match."""
        args = []
        for kw in kwargs.keys():
            args.append(f"{kw} ILIKE {kwargs['kw']}")
        query = f"SELECT * FROM {DB_TABLE}"
        if len(args) > 0:
            query += f" WHERE {' AND '.join(args)}"
        return self._query(query)

    def write(self, **kwargs):
        """Write a row to the database.

        :param kwargs: Values to write for each database; specify each column separately!"""
        pass