"""module contains all db related stuff"""
import contextlib
import logging
from typing import Any, Iterator, Protocol
from urllib.parse import urlparse
import MySQLdb as mdb
import xapian


LOGGER = logging.getLogger(__file__)


def __check_true__(val: str) -> bool:
    """Check whether the variable 'val' has the string value `true`."""
    return val.strip().lower() == "true"


def __parse_db_opts__(opts: str) -> dict:
    """Parse database options into their appropriate values.

    This assumes use of python-mysqlclient library."""
    allowed_opts = (
        "unix_socket", "connect_timeout", "compress", "named_pipe",
        "init_command", "read_default_file", "read_default_group",
        "cursorclass", "use_unicode", "charset", "collation", "auth_plugin",
        "sql_mode", "client_flag", "multi_statements", "ssl_mode", "ssl",
        "local_infile", "autocommit", "binary_prefix")
    conversion_fns = {
        **{opt: str for opt in allowed_opts},
        "connect_timeout": int,
        "compress": __check_true__,
        "use_unicode": __check_true__,
        # "cursorclass": __load_cursor_class__
        "client_flag": int,
        "multi_statements": __check_true__,
        # "ssl": __parse_ssl_options__,
        "local_infile": __check_true__,
        "autocommit": __check_true__,
        "binary_prefix": __check_true__
    }
    keyvals = tuple(filter(bool, opts.split("&")))
    if len(keyvals) > 0:
        keyvals = tuple(tuple(item.strip() for item in keyval.split("=")) for keyval in keyvals)
        def __check_opt__(opt):
            assert opt in allowed_opts, (
                f"Invalid database connection option ({opt}) provided.")
            return opt
        return {
            __check_opt__(key): conversion_fns[key](val)
            for key, val in keyvals
        }
    return {}


def parse_db_url(sql_uri: str) -> dict:
    """Parse the `sql_uri` variable into a dict of connection parameters."""
    parsed_db = urlparse(sql_uri)
    return {
        "host": parsed_db.hostname,
        "port": parsed_db.port or 3306,
        "user": parsed_db.username,
        "password": parsed_db.password,
        "database": parsed_db.path.strip("/").strip(),
        **__parse_db_opts__(parsed_db.query)
    }


# pylint: disable=missing-class-docstring, missing-function-docstring, too-few-public-methods
class Connection(Protocol):
    """Type Annotation for MySQLdb's connection object"""
    def cursor(self, *args, **kwargs) -> Any:
        """A cursor in which queries may be performed"""


@contextlib.contextmanager
def database_connection(sql_uri: str, logger: logging.Logger = LOGGER) -> Iterator[Connection]:
    """Connect to MySQL database."""
    connection = mdb.connect(**parse_db_url(sql_uri))
    try:
        yield connection
    except mdb.Error as _mbde:
        logger.error("DB error encountered", exc_info=True)
        connection.rollback()
    finally:
        connection.commit()
        connection.close()


@contextlib.contextmanager
def xapian_database(path):
    """Open xapian database read-only."""
    # pylint: disable-next=invalid-name
    db = xapian.Database(path)
    try:
        yield db
    finally:
        db.close()