#!/usr/bin/env python3

""" @package docstring
Self host healthcheck

A simple server monitoring software: ends an email in case of alarm.

Installation:
- Copy healthcheck.cfg in /usr/local/etc/healthcheck.cfg and customize it
- Copy healthcheck.py in /usr/local/bin/healthcheck.py

Usage:
Place a cron entry like this one:

* * * * *     root    python3 /usr/local/bin/healthcheck.py /usr/local/etc/healthcheck.cfg

The script will print current values and issue an alarm sending a mail if any of the values
exceeds the limit configured in healthcheck.cfg

@author Daniele Verducci <daniele.verducci@ichibi.eu>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
"""

import os
import sys
import logging
import traceback
import subprocess
import configparser
import time
from email.mime.multipart import MIMEMultipart
from email.mime.application import MIMEApplication
from email.mime.text import MIMEText
import smtplib
import socket
import getpass
import re
import locale
import json


NAME = 'healthcheck'
VERSION = '0.1'
DESCRIPTION = 'A simple server monitoring software'
EMAIL_START_SUBJECT_TPL = '\U0001F6A8 {}: {} ALARM!'
EMAIL_START_MESSAGE_TPL = 'Alarm for sensor {} on host {} on {}: {}'
EMAIL_END_SUBJECT_TPL = '\u2705 {}: {} OK'
EMAIL_END_MESSAGE_TPL = 'Alarm ceased for sensor {} on host {} on {}'
# Healthcheck saves the current status (alarms triggered, last run... in this file)
STATUS_FILE = '/tmp/healthcheck.tmp'

class Main:

	def __init__(self, configPath):
		''' Sets up locale (needed for parsing numbers) '''
		# Get system locale from $LANG (i.e. "en_GB.UTF-8")
		systemLocale = os.getenv('LANG')
		if not systemLocale:
			raise ValueError('System environment variabile $LANG is not set!')

		locale.setlocale(locale.LC_ALL, systemLocale)

		''' Reads the config '''
		self._log = logging.getLogger('main')

		if not os.path.exists(configPath) or not os.path.isfile(configPath):
			raise ValueError('configPath must be a file')

		self.config = configparser.ConfigParser(interpolation=None)	# Disable interpolation because contains regexp
		self.config.read(configPath)
		self.hostname = os.uname()[1]

	def run(self, dryRun):
		''' Runs the health checks '''

		# Load status
		status = Status()

		# Run checks based o the config
		for section in self.config:
			if section == 'DEFAULT':
				continue

			s = Settings(section, self.config)
			if s.disabled:
				self._log.info('Ignoring disabled check "{}"'.format(section))
				status.unsetAlarm(section)
				continue

			self._log.info('Checking "{}"'.format(section))

			error = self.check(s)
			if error:
				# Alarm!
				logging.warning('Alarm for {}: {}!'.format(section, error))
				if self.shouldNotify(section, s, status):
					status.setAlarm(section)
					if not dryRun:
						if s.mailto:
							self.sendAlmStartMail(s, error)
						if s.alarmCommand:
							self.executeAlarmCommand(s, error)
			elif status.getAlarmTriggeredTimestamp(section) is not None:
				logging.info('Alarm ceased for {}: OK!'.format(section))
				if s.notify_alarm_end and not dryRun and s.mailto:
					self.sendAlmEndMail(s)
				status.unsetAlarm(section)

		# Save updated status
		status.save()

	def shouldNotify(self, section, settings, status):
		almTriggeredTime = status.getAlarmTriggeredTimestamp(section)
		# Notify if alarm just started
		if almTriggeredTime is None:
			return True

		# Notify if NOTIFY=EVERY_RUN
		if settings.notify == 'EVERY_RUN':
			return True

		# Notify if time elapsed
		if settings.notify == 'ONCE_IN_MINUTES' and (time.time() - almTriggeredTime) > (settings.notify_minutes * 60):
			return True

		return False

	# Calls the provided command, checks the value parsing it with the provided regexp
	# and returns an error string, or null if the value is within its limits
	def check(self, config):
		# Check config
		if not config.command:
			return "bad config: COMMAND is mandatory"
		if not config.regexp:
			return "bad config: REGEXP is mandatory"

		# Run command
		stdout = ""
		ret = subprocess.run(config.command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
		if ret.stderr:
			self._log.info('{} subprocess stderr:\n{}'.format(config.command, ret.stderr.decode()))
		if ret.stdout:
			stdout = ret.stdout.decode()
			self._log.debug('{} subprocess stdout:\n{}'.format(config.command, stdout))
		if ret.returncode != 0:
			return 'the command exited with error code {} {}'.format(
				ret.returncode,
				'and error message "{}"'.format(ret.stderr.decode().strip()) if ret.stderr else ''
			)

		# Parse result with regex
		match = re.search(config.regexp, stdout, re.MULTILINE)
		if not match:
			return 'regexp didn\'t match anything'
		groups = match.groups()
		if len(groups) != 1:
			return 'regexp returns {} groups (expected exactly 1 group)'.format(len(matches))
		detectedValue = groups[0]

		# Compare detected value with equal, not equal, more than and less values
		logging.info('detected {}'.format(detectedValue))
		if config.alarm_string_equal and (detectedValue == config.alarm_string_equal):
			return 'value is "{}"'.format(detectedValue)
		if config.alarm_string_not_equal and (detectedValue != config.alarm_string_not_equal):
			return 'value is "{}", but should be "{}"'.format(detectedValue, config.alarm_string_not_equal)
		if config.alarm_value_equal and (locale.atof(detectedValue) == float(config.alarm_value_equal)):
			return 'value is {}'.format(detectedValue)
		if config.alarm_value_not_equal and (locale.atof(detectedValue) != float(config.alarm_value_not_equal)):
			return 'value is {}, but should be {}'.format(detectedValue, config.alarm_value_not_equal)
		if config.alarm_value_more_than and locale.atof(detectedValue) > float(config.alarm_value_more_than):
			return 'value is {}, but should not exceed {}'.format(locale.atof(detectedValue), config.alarm_value_more_than)
		if config.alarm_value_less_than and locale.atof(detectedValue) < float(config.alarm_value_less_than):
			return 'value is {}, but should be greater than {}'.format(locale.atof(detectedValue), config.alarm_value_less_than)

	def sendAlmStartMail(self, s, error):
		subject = EMAIL_START_SUBJECT_TPL.format(self.hostname, s.name)
		body = EMAIL_START_MESSAGE_TPL.format(
			s.name,
			self.hostname,
			time.strftime("%a, %d %b %Y %H:%M:%S"),
			error
		)
		self.sendMail(s, subject, body)

	def sendAlmEndMail(self, s):
		subject = EMAIL_END_SUBJECT_TPL.format(self.hostname, s.name)
		body = EMAIL_END_MESSAGE_TPL.format(
			s.name,
			self.hostname,
			time.strftime("%a, %d %b %Y %H:%M:%S")
		)
		self.sendMail(s, subject, body)

	def sendMail(self, s, subject, body):
		if s.smtphost:
			logging.info("Sending email to %s via %s", s.mailto, s.smtphost)
		else:
			logging.info("Sending email to %s using local smtp", s.mailto)

		# Create main message
		msg = MIMEMultipart()
		msg['Subject'] = subject
		if s.mailfrom:
			m_from = s.mailfrom
		else:
			m_from = s.username + "@" + s.hostname
		msg['From'] = m_from
		msg['To'] = ', '.join(s.mailto)
		msg.preamble = 'This is a multi-part message in MIME format.'

		# Add base text
		txt = MIMEText(body)
		msg.attach(txt)

		# Send the message
		if s.smtpssl and s.smtphost:
			smtp = smtplib.SMTP_SSL(s.smtphost, timeout=300)
		else:
			smtp = smtplib.SMTP(timeout=300)

		if s.smtphost:
			smtp.connect(s.smtphost)
		else:
			smtp.connect()
		if s.smtpuser or s.smtppass:
			smtp.login(s.smtpuser, s.smtppass)
		smtp.sendmail(m_from, s.mailto, msg.as_string())
		smtp.quit()

	def executeAlarmCommand(self, s, error):
		cmdToRun = s.alarmCommand
		cmdToRun = cmdToRun.replace('%%CHECKNAME%%', s.name)
		cmdToRun = cmdToRun.replace('%%HOSTNAME%%', self.hostname)
		cmdToRun = cmdToRun.replace('%%DATETIME%%', time.strftime("%a, %d %b %Y %H:%M:%S"))
		cmdToRun = cmdToRun.replace('%%ERROR%%', error)

		logging.debug("Executing alarm command %s", cmdToRun)

		ret = subprocess.run(cmdToRun, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
		if ret.stderr:
			self._log.info('{} subprocess stderr:\n{}', cmdToRun, ret.stderr.decode())
		if ret.stdout:
			stdout = ret.stdout.decode()
			self._log.debug('{} subprocess stdout:\n{}', cmdToRun, stdout)
		if ret.returncode != 0:
			self._log.error('subprocess {} exited with error code {}'.format(cmdToRun, ret.returncode))


class Status:
	''' Represents the current status (alarms triggered, last run...) '''

	def __init__(self):
		try:
			with open(STATUS_FILE, 'r') as openfile:
				self.status = json.load(openfile)
		except FileNotFoundError:
			self.status =  {
				'lastRun': 0,	# unix time in seconds
				'alarms': {},	# key-value, alarmName : alarmTriggeredTimestamp
			}

	def save(self):
		self.status['lastRun'] = time.time()
		jo = json.dumps(self.status)
		with open(STATUS_FILE, "w") as outfile:
			outfile.write(jo)

	def setAlarm(self, almName):
		self.status['alarms'][almName] = time.time()

	def unsetAlarm(self, almName):
		self.status['alarms'].pop(almName, None)

	def getAlarmTriggeredTimestamp(self, almName):
		return self.status['alarms'].get(almName, None)


class Settings:
	''' Represents settings for a check '''

	EMAIL_LIST_SEP = ','

	def __init__(self, name, config):
		self.config = config
		self.hostname = socket.getfqdn()
		self.username = getpass.getuser()

		## Check name
		self.name = name
		## Disabled
		self.disabled = self.getBoolean(name, 'DISABLED', False)
		## Email server connection data
		self.smtphost = self.getStr(name, 'SMTPHOST', None)
		self.smtpuser = self.getStr(name, 'SMTPUSER', None)
		self.smtppass = self.getStr(name, 'SMTPPASS', None)
		self.smtpssl = self.getBoolean(name, 'SMTPSSL', False)
		## List of email address to notify in case of alarms (disabled if missing)
		mailtoList = self.getStr(name, 'MAILTO', None)
		if mailtoList:
			self.mailto = [ x.strip() for x in mailtoList.strip().split(self.EMAIL_LIST_SEP) ]
		else:
			self.mailto = None
		## Command to execute in case of alarms (disabled if missing)
		self.alarmCommand = self.getStr(name, 'ALARM_COMMAND', None)
		## Sender address for the notification email
		self.mailfrom = self.getStr(name, 'MAILFROM', getpass.getuser()+'@'+socket.gethostname())
		## Values to compare
		self.alarm_string_equal = self.getStr(name, 'ALARM_STRING_EQUAL', None)
		self.alarm_string_not_equal = self.getStr(name, 'ALARM_STRING_NOT_EQUAL', None)
		self.alarm_value_equal = self.getStr(name, 'ALARM_VALUE_EQUAL', None)
		self.alarm_value_not_equal = self.getStr(name, 'ALARM_VALUE_NOT_EQUAL', None)
		self.alarm_value_more_than = self.getStr(name, 'ALARM_VALUE_MORE_THAN', None)
		self.alarm_value_less_than = self.getStr(name, 'ALARM_VALUE_LESS_THAN', None)
		## Notification policy
		self.notify = self.getEnum(name, 'NOTIFY', 'EVERY_RUN', ['EVERY_RUN', 'START', 'ONCE_IN_MINUTES'])
		self.notify_minutes = self.getInt(name, 'NOTIFY_MINUTES', 0)
		self.notify_alarm_end = self.getBoolean(name, 'NOTIFY_ALARM_END', True)
		## Command to obtain the value for comparation
		self.command = self.getStr(name, 'COMMAND', None)
		## Regexp to extract value from command output (default to match full string)
		self.regexp = self.getStr(name, 'REGEXP', '(.*)')

	def getStr(self, name, key, defaultValue):
		try:
			return self.config.get(name, key)
		except configparser.NoOptionError:
			return defaultValue

	def getInt(self, name, key, defaultValue):
		return int(self.getStr(name, key, defaultValue))

	def getBoolean(self, name, key, defaultValue):
		try:
			return self.config.getboolean(name, key)
		except configparser.NoOptionError:
			return defaultValue

	def getEnum(self, name, key, defaultValue, values):
		val = self.getStr(name, key, defaultValue)
		if not val in values:
			raise ValueError("Invalid value {} for configuration {}: expected one of {}".format(val, key, ', '.join(values)))
		return val


if __name__ == '__main__':
	import argparse

	parser = argparse.ArgumentParser(
		prog = NAME + '.py',
		description = NAME + ' ' + VERSION + '\n' + DESCRIPTION,
		formatter_class = argparse.RawTextHelpFormatter
	)
	parser.add_argument('configFile', help="configuration file path")
	parser.add_argument('-q', '--quiet', action='store_true', help="suppress non-essential output")
	parser.add_argument('-d', '--dry-run', action='store_true', help="do not send emails or execute completion script")
	args = parser.parse_args()

	if args.quiet:
		level = logging.WARNING
	else:
		level = logging.INFO
	logging.basicConfig(level=level)

	try:
		main = Main(args.configFile)
		main.run(args.dry_run)
	except Exception as e:
		logging.critical(traceback.format_exc())
		print('ERROR: {}'.format(e))
		sys.exit(1)

	sys.exit(0)