#!/usr/bin/bash

# BEGIN: Variables
## Duration to wait to see if service has come back up
DURATION=10
## Wait duration to send next part of message
WAIT=1

## Test flag
TEST=0

## Email addresses
NOTIFY_EMAIL=recipient@domain.com
MAIL_FROM=username@domain.net
FROM_DOMAIN=` echo $FROM_EMAIL | cut -d @ -f 2 `
DAMAIN=` echo $NOTIFY_EMAIL | cut -d @ -f 2 `

# END: Variables


# BEGIN: Helper Functions

send_email () {
	local MESSAGE="${1:?"send_email: No message was passed through"}"
	sendmail $NOTIFY_EMAIL <<< "$MESSAGE"

}


: "
The only option is to manually telnet to the smtp port on the authoritative mailserver for the target domain. As otherwise unless a mail-host is configured as an email relay, you will be unable to send an email to a user outside of the mailservers domain (without authentication). 
"
do_emergency_email () {
	local MESSAGE="${1:-"The Postfix service has failed to come up on `hostname` (`hostname -i`) after a service restart. Please ssh into server to troubleshoot the issues."}"
	## Getting a mailserver IP for manual message
	MAILSERVER=`dig $DOMAIN mx | grep -Eo '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+' | head -n 1`

	## Setting up coprocess to send commands to telnet session coproc TELNET { telnet $MAILSERVER 25; }

	## Commands to send email manually
	local -a commands=(
		"ehlo $FROM_DOMAIN\n"
		"mail from: <$MAIL_FROM>\n"
		"rcpt to: <$NOTIFY_EMAIL>\n"
		"data\n"
		"Subject: Postfix Service Failure\nFrom: $MAIL_FROM\nTo: $NOTIFY_EMAIL\n"
		"$MESSAGE\n\n.\n"
		"quit\n"
	)

	## Iterate through commands and send them to coprocesses
	### We need to wait before each command as the remote mailserver will not catch everything otherwise.
	for i in ${!commands[@]}; do
		COMMAND="${commands[$i]}"
		echo -e "$COMMAND" >&${TELNET[1]}
		sleep $WAIT
	done
}

# END: Helper Functions


# BEGIN: Test Check 

if [[ $TEST -eq 1 ]]; then
	MESSAGE_1="
This is a test message to verify that postfix can send an email
"
	send_email "$MESSAGE_1"

	MESSAGE_2="This is a test email to make sure the postfix crash workaround email works"

	do_emergency_email "$MESSAGE_2"
	exit
fi

# END: Test Check


# BEGIN: Work

if [[ `systemctl is-active postfix`  != 'active' ]]; then
	systemctl restart postfix

	sleep $DURATION

	SERVICE_STATUS=` systemctl is-active postfix `

	if [[ "$SERVICE_STATUS" == 'active' ]]; then
		MESSAGE="
SUBJECT: Postfix Service Failure
FROM: root
TO: $NOTIFY_EMAIL

The postfix service on `hostname` (`hostname -i`) was found to be not running.

The service has been restarted, and after waiting $DURATION seconds it was found to be $SERVICE_STATUS.
"
		send_email "$MESSAGE"
	else
		do_emergency_email
	fi
fi

# END: Work