#!/usr/bin/env python3
# -*- coding: utf-8; py-indent-offset: 4 -*-
#
# Author:  Linuxfabrik GmbH, Zurich, Switzerland
# Contact: info (at) linuxfabrik (dot) ch
#          https://www.linuxfabrik.ch/
# License: The Unlicense, see LICENSE file.

# https://github.com/Linuxfabrik/monitoring-plugins/blob/main/CONTRIBUTING.md

"""See the check's README for more details."""

import argparse
import sys

import lib.args
import lib.base
import lib.db_mysql
import lib.human
from lib.globals import STATE_OK, STATE_UNKNOWN, STATE_WARN

__author__ = 'Linuxfabrik GmbH, Zurich/Switzerland'
__version__ = '2026040801'

DESCRIPTION = """Checks how effectively MySQL/MariaDB caches threads for re-use. A low cache hit rate
means the server frequently creates new threads, which is expensive.
Alerts when the cache hit rate is too low."""

DEFAULT_DEFAULTS_FILE = '/var/spool/icinga2/.my.cnf'
DEFAULT_DEFAULTS_GROUP = 'client'
DEFAULT_TIMEOUT = 3


def parse_args():
    """Parse command line arguments using argparse."""
    parser = argparse.ArgumentParser(description=DESCRIPTION)

    parser.add_argument(
        '-V',
        '--version',
        action='version',
        version=f'%(prog)s: v{__version__} by {__author__}',
    )

    parser.add_argument(
        '--always-ok',
        help=lib.args.help('--always-ok'),
        dest='ALWAYS_OK',
        action='store_true',
        default=False,
    )

    parser.add_argument(
        '--defaults-file',
        help='MySQL/MariaDB cnf file to read parameters like user, host and password from (instead of specifying them on the command line). '
        'Example: `/var/spool/icinga2/.my.cnf`. '
        'Default: %(default)s',
        dest='DEFAULTS_FILE',
        default=DEFAULT_DEFAULTS_FILE,
    )

    parser.add_argument(
        '--defaults-group',
        help=lib.args.help('--defaults-group') + ' Default: %(default)s',
        dest='DEFAULTS_GROUP',
        default=DEFAULT_DEFAULTS_GROUP,
    )

    parser.add_argument(
        '--timeout',
        help=lib.args.help('--timeout') + ' Default: %(default)s (seconds)',
        dest='TIMEOUT',
        type=int,
        default=DEFAULT_TIMEOUT,
    )

    args, _ = parser.parse_known_args()
    return args


def get_vars(conn):
    # Do not implement `get_all_vars()`, just fetch the ones we need for this check.
    # Without the GLOBAL modifier, SHOW VARIABLES displays the values that are used for
    # the current connection to MariaDB.
    sql = """
        show global variables
        where variable_name like 'have_threadpool'
            or variable_name like 'thread_cache_size'
            ;
          """
    return lib.base.coe(lib.db_mysql.select(conn, sql))


def get_status(conn):
    # Do not implement `get_all_vars()`, just fetch the ones we need for this check.
    # Without the GLOBAL modifier, SHOW STATUS displays the values that are used for
    # the current connection to MariaDB.
    sql = """
        show global status
        where variable_name like 'Connections'
            or variable_name like 'Threads_created'
            or variable_name like 'Uptime'
            ;
          """
    return lib.base.coe(lib.db_mysql.select(conn, sql))


def main():
    """The main function. This is where the magic happens."""

    # logic taken from mysqltuner.pl:mysql_stats(), section # Thread cache, v1.9.8
    # including variable names

    # parse the command line
    try:
        args = parse_args()
    except SystemExit:
        sys.exit(STATE_UNKNOWN)

    mysql_connection = {
        'defaults_file': args.DEFAULTS_FILE,
        'defaults_group': args.DEFAULTS_GROUP,
        'timeout': args.TIMEOUT,
    }
    conn = lib.base.coe(lib.db_mysql.connect(mysql_connection))
    lib.base.coe(lib.db_mysql.check_select_privileges(conn))

    myvar = lib.db_mysql.lod2dict(get_vars(conn))
    mystat = lib.db_mysql.lod2dict(get_status(conn))
    lib.db_mysql.close(conn)

    # init some vars
    msg = ''
    state = STATE_OK
    perfdata = ''

    # calculations
    mycalc = {}
    mycalc['thread_cache_hit_rate'] = 100 - round(
        (int(mystat['Threads_created']) / int(mystat['Connections'])) * 100, 1
    )

    # Thread cache
    if myvar.get('have_threadpool', False) and myvar['have_threadpool'] == 'YES':
        # https://www.percona.com/doc/percona-server/5.7/performance/threadpool.html#status-variables
        # When thread pool is enabled, the value of the thread_cache_size variable
        # is ignored. The Threads_cached status variable contains 0 in this case.
        msg += 'Thread cache not used with thread pool enabled.'
    else:
        if int(myvar['thread_cache_size']) == 0:
            state = STATE_WARN

            # build the message
            msg += (
                f'Thread cache is disabled'
                f'{lib.base.state2str(state, prefix=" ")}'
                f'. Set thread_cache_size to 4'
                f' as a starting value.'
            )
        else:
            msg += (
                f'{mycalc["thread_cache_hit_rate"]}%'
                f' thread cache hit rate'
                f' ({lib.human.number2human(mystat["Threads_created"])}'
                f' threads created /'
                f' {lib.human.number2human(mystat["Connections"])}'
                f' connections)'
            )
            if int(mystat['Uptime']) < 3600:
                # only alert if cache is warmed up
                msg += '. Cache is warming up.'
            elif mycalc['thread_cache_hit_rate'] <= 50:
                state = STATE_WARN
                msg += (
                    f'{lib.base.state2str(state, prefix=" ")}'
                    f'. Set thread_cache_size >'
                    f' {myvar["thread_cache_size"]}.'
                )
            else:
                msg += '.'

    perfdata += lib.base.get_perfdata(
        'mysql_thread_cache_size',
        myvar['thread_cache_size'],
        uom='B',
        _min=0,
    )

    perfdata += lib.base.get_perfdata(
        'mysql_connections',
        mystat['Connections'],
        uom='c',
        _min=0,
    )
    perfdata += lib.base.get_perfdata(
        'mysql_threads_created',
        mystat['Threads_created'],
        uom='c',
        _min=0,
    )

    perfdata += lib.base.get_perfdata(
        'mysql_thread_cache_hit_rate',
        mycalc['thread_cache_hit_rate'],
        uom='%',
        _min=0,
        _max=100,
    )

    # over and out
    lib.base.oao(msg, state, perfdata, always_ok=args.ALWAYS_OK)


if __name__ == '__main__':
    try:
        main()
    except Exception:
        lib.base.cu()
