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#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License, version 2.0, as
# published by the Free Software Foundation.
#
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"""Implementing pooling of connections to MySQL servers."""

from __future__ import annotations

import asyncio
import os
import random
import re
import sys

from types import TracebackType
from typing import TYPE_CHECKING, Any, Dict, NoReturn, Optional, Tuple, Type, Union
from uuid import UUID, uuid4

from mysql.connector.constants import CNX_POOL_ARGS

try:
    import dns.asyncresolver
    import dns.exception
except ImportError:
    HAVE_DNSPYTHON = False
else:
    HAVE_DNSPYTHON = True

from ..errors import (
    Error,
    InterfaceError,
    NotSupportedError,
    PoolError,
    ProgrammingError,
)
from ..pooling import DEFAULT_CONFIGURATION, generate_pool_name, read_option_files
from .connection import MySQLConnection

if TYPE_CHECKING:
    from .abstracts import MySQLConnectionAbstract


CONNECTION_POOL_LOCK = asyncio.Lock()
CNX_POOL_MAXSIZE = 32
CNX_POOL_MAXNAMESIZE = 64
CNX_POOL_NAMEREGEX = re.compile(r"[^a-zA-Z0-9._:\-*$#]")
MYSQL_CNX_CLASS: Union[type, Tuple[type, ...]] = (MySQLConnection,)

_CONNECTION_POOLS: Dict[str, MySQLConnectionPool] = {}


async def _get_pooled_connection(**kwargs: Any) -> PooledMySQLConnection:
    """Return a pooled MySQL connection."""
    # If no pool name specified, generate one
    pool_name = (
        kwargs["pool_name"] if "pool_name" in kwargs else generate_pool_name(**kwargs)
    )

    # Setup the pool, ensuring only 1 thread can update at a time
    if pool_name not in _CONNECTION_POOLS:
        pool = MySQLConnectionPool(**kwargs)
        await pool.initialize_pool()

        async with CONNECTION_POOL_LOCK:
            _CONNECTION_POOLS[pool_name] = pool
    elif isinstance(_CONNECTION_POOLS[pool_name], MySQLConnectionPool):
        # pool_size must be the same
        check_size = _CONNECTION_POOLS[pool_name].pool_size
        if "pool_size" in kwargs and kwargs["pool_size"] != check_size:
            raise PoolError("Size can not be changed for active pools.")

    # Return pooled connection
    try:
        return await _CONNECTION_POOLS[pool_name].get_connection()
    except AttributeError:
        raise InterfaceError(
            f"Failed getting connection from pool '{pool_name}'"
        ) from None


async def _get_failover_connection(
    **kwargs: Any,
) -> Union[PooledMySQLConnection, MySQLConnectionAbstract]:
    """Return a MySQL connection and try to failover if needed.

    An InterfaceError is raise when no MySQL is available. ValueError is
    raised when the failover server configuration contains an illegal
    connection argument. Supported arguments are user, password, host, port,
    unix_socket and database. ValueError is also raised when the failover
    argument was not provided.

    Returns MySQLConnection instance.
    """
    config = kwargs.copy()
    try:
        failover = config["failover"]
    except KeyError:
        raise ValueError("failover argument not provided") from None
    del config["failover"]

    support_cnx_args = {
        "user",
        "password",
        "host",
        "port",
        "unix_socket",
        "database",
        "pool_name",
        "pool_size",
        "priority",
    }

    # First check if we can add all use the configuration
    priority_count = 0
    for server in failover:
        diff = set(server.keys()) - support_cnx_args
        if diff:
            arg = "s" if len(diff) > 1 else ""
            lst = ", ".join(diff)
            raise ValueError(
                f"Unsupported connection argument {arg} in failover: {lst}"
            )
        if hasattr(server, "priority"):
            priority_count += 1

        server["priority"] = server.get("priority", 100)
        if server["priority"] < 0 or server["priority"] > 100:
            raise InterfaceError(
                "Priority value should be in the range of 0 to 100, "
                f"got : {server['priority']}"
            )
        if not isinstance(server["priority"], int):
            raise InterfaceError(
                "Priority value should be an integer in the range of 0 to "
                f"100, got : {server['priority']}"
            )

    if 0 < priority_count < len(failover):
        raise ProgrammingError(
            "You must either assign no priority to any "
            "of the routers or give a priority for "
            "every router"
        )

    server_directory = {}
    server_priority_list = []
    for server in sorted(failover, key=lambda x: x["priority"], reverse=True):
        if server["priority"] not in server_directory:
            server_directory[server["priority"]] = [server]
            server_priority_list.append(server["priority"])
        else:
            server_directory[server["priority"]].append(server)

    for priority in server_priority_list:
        failover_list = server_directory[priority]
        for _ in range(len(failover_list)):
            last = len(failover_list) - 1
            index = random.randint(0, last)
            server = failover_list.pop(index)
            new_config = config.copy()
            new_config.update(server)
            new_config.pop("priority", None)
            try:
                return await connect(**new_config)
            except Error:
                # If we failed to connect, we try the next server
                pass

    raise InterfaceError("Unable to connect to any of the target hosts")


async def connect(
    *args: Any, **kwargs: Any
) -> Union[PooledMySQLConnection, MySQLConnectionAbstract]:
    """Creates a MySQL connection object.

    In its simpliest form, `connect()` will open a connection to a
    MySQL server and return a `MySQLConnectionAbstract` subclass
    object such as `MySQLConnection` or `CMySQLConnection`.

    Args:
        *args: N/A.
        **kwargs: For a complete list of possible arguments, see [1]. If no arguments
                  are given, it uses the already configured or default values.

    Returns:
        A `MySQLConnectionAbstract` subclass instance (such as `MySQLConnection`)
        or a `PooledMySQLConnection` instance.

    Raises:
        `mysql.connector.errors.NotSupportedError`: if pooled connection is not supported
        for the Python version and OS that are being used.

    Examples:
        A connection with the MySQL server can be established using either the
        `mysql.connector.aio.connect()` method or a `MySQLConnectionAbstract` subclass:
        ```
        >>> from mysql.connector.aio import MySQLConnection
        >>>
        >>> cnx1 = await mysql.connector.aio.connect(user='joe', database='test')
        >>> cnx2 = MySQLConnection(user='joe', database='test')
        >>>
        ```
    References:
        [1]: https://dev.mysql.com/doc/connector-python/en/connector-python-connectargs.html
    """
    # DNS SRV
    dns_srv = kwargs.pop("dns_srv") if "dns_srv" in kwargs else False

    if not isinstance(dns_srv, bool):
        raise InterfaceError("The value of 'dns-srv' must be a boolean")

    if dns_srv:
        if not HAVE_DNSPYTHON:
            raise InterfaceError(
                "MySQL host configuration requested DNS "
                "SRV. This requires the Python dnspython "
                "module. Please refer to documentation"
            )
        if "unix_socket" in kwargs:
            raise InterfaceError(
                "Using Unix domain sockets with DNS SRV lookup is not allowed"
            )
        if "port" in kwargs:
            raise InterfaceError(
                "Specifying a port number with DNS SRV lookup is not allowed"
            )
        if "failover" in kwargs:
            raise InterfaceError(
                "Specifying multiple hostnames with DNS SRV look up is not allowed"
            )
        if "host" not in kwargs:
            kwargs["host"] = DEFAULT_CONFIGURATION["host"]

        try:
            srv_records = await dns.asyncresolver.query(kwargs["host"], "SRV")
        except dns.exception.DNSException:
            raise InterfaceError(
                f"Unable to locate any hosts for '{kwargs['host']}'"
            ) from None

        failover = []
        for srv in srv_records:
            failover.append(
                {
                    "host": srv.target.to_text(omit_final_dot=True),
                    "port": srv.port,
                    "priority": srv.priority,
                    "weight": srv.weight,
                }
            )

        failover.sort(key=lambda x: (x["priority"], -x["weight"]))
        kwargs["failover"] = [
            {"host": srv["host"], "port": srv["port"]} for srv in failover
        ]

    # Failover
    if "failover" in kwargs:
        return await _get_failover_connection(**kwargs)

    # Pooled connections
    try:
        if any(key in kwargs for key in CNX_POOL_ARGS):
            return await _get_pooled_connection(**kwargs)
    except NameError:
        # No pooling
        pass

    # Option files
    if "read_default_file" in kwargs:
        kwargs["option_files"] = kwargs["read_default_file"]
        kwargs.pop("read_default_file")

    if "option_files" in kwargs:
        new_config = read_option_files(**kwargs)
        return await connect(**new_config)

    if "use_pure" in kwargs:
        del kwargs["use_pure"]  # Remove 'use_pure' from kwargs

    cnx = MySQLConnection(*args, **kwargs)
    await cnx.connect()
    return cnx


def _check_support() -> None:
    """Raises error if the Python version and OS combination is not
    supported for Pooling."""
    py_version_info = sys.version_info
    if os.name == "nt" and py_version_info.major == 3 and py_version_info.minor <= 10:
        raise NotSupportedError(
            "Pooled connections are not supported for Python versions "
            "lower than 3.11 on Windows"
        )


class PooledMySQLConnection:
    """Class holding a MySQL Connection in a pool
    PooledMySQLConnection is used by MySQLConnectionPool to return an
    instance holding a MySQL connection. It works like a MySQLConnection
    except for methods like close() and config().
    The close()-method will add the connection back to the pool rather
    than disconnecting from the MySQL server.
    Configuring the connection have to be done through the MySQLConnectionPool
    method set_config(). Using config() on pooled connection will raise a
    PoolError.
    Attributes:
        pool_name (str): Returns the name of the connection pool to which the
                         connection belongs.
    """

    def __init__(self, pool: MySQLConnectionPool, cnx: MySQLConnectionAbstract) -> None:
        """Constructor.
        Args:
            pool: A `MySQLConnectionPool` instance.
            cnx: A `MySQLConnectionAbstract` subclass instance.
        """
        _check_support()

        if not isinstance(pool, MySQLConnectionPool):
            raise AttributeError("pool must be an instance of MySQLConnectionPool")
        if not isinstance(cnx, MYSQL_CNX_CLASS):
            raise AttributeError("cnx should be an instance of MySQLConnection")
        self._cnx_pool: MySQLConnectionPool = pool
        self._cnx: MySQLConnectionAbstract = cnx

    async def __aenter__(self) -> PooledMySQLConnection:
        return self

    async def __aexit__(
        self,
        exc_type: Type[BaseException],
        exc_value: BaseException,
        traceback: TracebackType,
    ) -> None:
        await self.close()

    def __getattr__(self, attr: Any) -> Any:
        """Calls attributes of the MySQLConnection instance"""
        return getattr(self._cnx, attr)

    async def close(self) -> None:
        """Do not close, but adds connection back to pool.
        For a pooled connection, close() does not actually close it but returns it
        to the pool and makes it available for subsequent connection requests. If the
        pool configuration parameters are changed, a returned connection is closed
        and reopened with the new configuration before being returned from the pool
        again in response to a connection request.
        """
        cnx = self._cnx
        try:
            if self._cnx_pool.can_reset_session and await cnx.is_connected():
                await cnx.reset_session()
        finally:
            await self._cnx_pool.add_connection(cnx)
            self._cnx = None

    @staticmethod
    def config(**kwargs: Any) -> NoReturn:
        """Configuration is done through the pool.
        For pooled connections, the `config()` method raises a `PoolError`
        exception. Configuration for pooled connections should be done
        using the pool object.
        """
        raise PoolError(
            "Configuration for pooled connections should be done through the "
            "pool itself"
        )

    @property
    def pool_name(self) -> str:
        """Returns the name of the connection pool to which the connection belongs."""
        return self._cnx_pool.pool_name


class MySQLConnectionPool:
    """Class defining a pool of MySQL connections"""

    def __init__(
        self,
        pool_size: int = 5,
        pool_name: Optional[str] = None,
        pool_reset_session: bool = True,
        **kwargs: Any,
    ) -> None:
        """Constructor.

        Initialize a MySQL connection pool with a maximum number of
        connections set to `pool_size`.

        NOTE: The coroutine `await cnxpool.initialize_pool(**dbconfig)` must be called
        after initializing this class to open up the pool of required number of database
        connections and making the instance of MySQLConnectionPool ready-to-use.
        Contents of `dbconfig` is described in [1].

        Args:
            pool_name: The pool name. If this argument is not given, Connector/Python
                       automatically generates the name, composed from whichever of
                       the host, port, user, and database connection arguments are
                       given in kwargs, in that order.
            pool_size:  The pool size. If this argument is not given, the default is 5.
            pool_reset_session: Whether to reset session variables when the connection
                                is returned to the pool.

        Examples:
            ```
            >>> dbconfig = {
            >>>     "database": "test",
            >>>     "user":     "joe",
            >>> }
            >>> # initialize the MySQLConnectionPool instance
            >>> cnxpool = mysql.connector.aio.pooling.MySQLConnectionPool(
            >>>             pool_name = "mypool",
            >>>             pool_size = 3,
            >>> )
            >>> # Open up the pool of connections
            >>> await cnxpool.initialize_pool(**dbconfig)
            >>> # cnxpool is ready to be used ...
            ```
        References:
            [1]: https://dev.mysql.com/doc/connector-python/en/connector-python-connectargs.html
        """
        _check_support()

        self._pool_size: Optional[int] = None
        self._pool_name: Optional[str] = None
        self._reset_session: bool = pool_reset_session
        self._set_pool_size(pool_size)
        if pool_name:
            self._set_pool_name(pool_name)
        self._cnx_config: Dict[str, Any] = kwargs
        self._cnx_queue: asyncio.Queue[MySQLConnectionAbstract] = asyncio.Queue(
            self._pool_size
        )
        self._config_version: UUID = uuid4()

    async def initialize_pool(self) -> None:
        """Opens the connection pool and fill with MySQL database connections.

        This coroutine must be called after initializing an instance of MySQLConnectionPool
        to make the build the pool of connections and make the instance ready to be used.

        Args:
            **kwargs: Connection arguments, as described in [1].

        References:
            [1]: https://dev.mysql.com/doc/connector-python/en/connector-python-connectargs.html
        """
        if not self._pool_name:
            async with CONNECTION_POOL_LOCK:
                self._set_pool_name(generate_pool_name(**self._cnx_config))
        if self._cnx_config:
            await self.set_config(**self._cnx_config)
            cnt = 0
            while cnt < self._pool_size:
                await self.add_connection()
                cnt += 1

    @property
    def pool_name(self) -> str:
        """Returns the name of the connection pool."""
        return self._pool_name

    @property
    def pool_size(self) -> int:
        """Returns number of connections managed by the pool."""
        return self._pool_size

    @property
    def can_reset_session(self) -> bool:
        """Returns whether to reset session."""
        return self._reset_session

    async def set_config(self, **kwargs: Any) -> None:
        """Set the connection configuration for `MySQLConnectionAbstract` subclass instances.
        This method sets the configuration used for creating `MySQLConnectionAbstract`
        subclass instances such as `MySQLConnection`. See [1] for valid
        connection arguments.
        Args:
            **kwargs: Connection arguments - for a complete list of possible
                      arguments, see [1].
        Raises:
            PoolError: When a connection argument is not valid, missing
                       or not supported by `MySQLConnectionAbstract`.
        References:
            [1]: https://dev.mysql.com/doc/connector-python/en/connector-python-connectargs.html
        """
        if not kwargs:
            return

        try:
            # test if we're able to connect using the provided connection options
            cnx = await connect(**kwargs)
            await cnx.disconnect()
            async with CONNECTION_POOL_LOCK:
                self._cnx_config = kwargs
                self._config_version = uuid4()
        except Exception as err:
            raise PoolError(f"Connection configuration not valid: {err}") from err

    def _set_pool_size(self, pool_size: int) -> None:
        """Set the size of the pool
        This method sets the size of the pool but it will not resize the pool.
        Raises an AttributeError when the pool_size is not valid. Invalid size
        is 0, negative or higher than pooling.CNX_POOL_MAXSIZE.
        """
        if pool_size <= 0 or pool_size > CNX_POOL_MAXSIZE:
            raise AttributeError(
                "Pool size should be higher than 0 and lower or equal to "
                f"{CNX_POOL_MAXSIZE}"
            )
        self._pool_size = pool_size

    def _set_pool_name(self, pool_name: str) -> None:
        r"""Set the name of the pool.
        This method checks the validity and sets the name of the pool.
        Raises an AttributeError when pool_name contains illegal characters
        ([^a-zA-Z0-9._\-*$#]) or is longer than pooling.CNX_POOL_MAXNAMESIZE.
        """
        if CNX_POOL_NAMEREGEX.search(pool_name):
            raise AttributeError(f"Pool name '{pool_name}' contains illegal characters")
        if len(pool_name) > CNX_POOL_MAXNAMESIZE:
            raise AttributeError(f"Pool name '{pool_name}' is too long")
        self._pool_name = pool_name

    def _queue_connection(self, cnx: MySQLConnectionAbstract) -> None:
        """Put connection back in the queue
        This method is putting a connection back in the queue. It will not
        acquire a lock as the methods using _queue_connection() will have it
        set.
        Raises `PoolError` on errors.
        """
        if not isinstance(cnx, MYSQL_CNX_CLASS):
            raise PoolError(
                "Connection instance not subclass of MySQLConnectionAbstract"
            )

        try:
            self._cnx_queue.put_nowait(cnx)
        except asyncio.QueueFull as err:
            raise PoolError("Failed adding connection; queue is full") from err

    async def add_connection(
        self, cnx: Optional[MySQLConnectionAbstract] = None
    ) -> None:
        """Adds a connection to the pool.
        This method instantiates a `MySQLConnection` using the configuration
        passed when initializing the `MySQLConnectionPool` instance or using
        the `set_config()` method.
        If cnx is a `MySQLConnection` instance, it will be added to the
        queue.
        Args:
            cnx: The `MySQLConnectionAbstract` subclass object to be added to
                 the pool. If this argument is missing (aka `None`), the pool
                 creates a new connection and adds it.
        Raises:
            PoolError: When no configuration is set, when no more
                       connection can be added (maximum reached) or when the connection
                       can not be instantiated.
        """
        if not self._cnx_config:
            raise PoolError("Connection configuration not available")

        if self._cnx_queue.full():
            raise PoolError("Failed adding connection; queue is full")

        if not cnx:
            cnx = await connect(**self._cnx_config)
            try:
                if (
                    self._reset_session
                    and self._cnx_config["compress"]
                    and cnx.get_server_version() < (5, 7, 3)
                ):
                    raise NotSupportedError(
                        "Pool reset session is not supported with "
                        "compression for MySQL server version 5.7.2 "
                        "or earlier"
                    )
            except KeyError:
                pass

            cnx.pool_config_version = self._config_version
        else:
            if not isinstance(cnx, MYSQL_CNX_CLASS):
                raise PoolError(
                    "Connection instance not subclass of MySQLConnectionAbstract"
                )

        self._queue_connection(cnx)

    async def get_connection(self) -> PooledMySQLConnection:
        """Gets a connection from the pool.
        This method returns an PooledMySQLConnection instance which
        has a reference to the pool that created it, and the next available
        MySQL connection.
        When the MySQL connection is not connect, a reconnect is attempted.
        Returns:
            A `PooledMySQLConnection` instance.
        Raises:
            PoolError: On errors.
        """

        try:
            cnx = self._cnx_queue.get_nowait()
        except asyncio.QueueEmpty as err:
            raise PoolError("Failed getting connection; pool exhausted") from err

        if (
            not await cnx.is_connected()
            or self._config_version != cnx.pool_config_version
        ):
            try:
                cnx._set_connection_options(**self._cnx_config)
                await cnx.reconnect()
            except InterfaceError:
                self._queue_connection(cnx)
                raise
            cnx.pool_config_version = self._config_version

        return PooledMySQLConnection(self, cnx)

    async def _remove_connections(self) -> int:
        """Close all connections
        This method closes all connections and returns the number of connections it closed.
        This method should be used internally while cleaning-up the connection pool by closing each
        and every active connection objects currently residing in the pool.

        Returns:
            An integer defining the number of open connections closed during clean-up.
        Raises:
            PoolError: On errors while fetching connections from the pool or while disconnecting
            an open connection.
        """
        cnt = 0
        cnxq = self._cnx_queue
        while cnxq.qsize():
            try:
                cnx = cnxq.get_nowait()
                await cnx.disconnect()
                cnt += 1
            except asyncio.QueueEmpty:
                return cnt
            except PoolError:
                raise
            except Error:
                # Any other error when closing means connection is closed
                pass

        return cnt

    async def close_pool(self) -> int:
        """Cleans up the connection pool
        This public method gracefully shuts down the connection pool by disconnecting all of the
        open connections currently active in the pool.

        Returns:
            An integer defining the number of open connections closed while shutting down the pool.
        Raises:
            PoolError: On errors while fetching connections from the pool or while disconnecting
            an open connection.
        """
        return await self._remove_connections()
