#!/usr/bin/env bash
#############################################################################
# Double checks stored IP is in a valid format and, if so, checks for any   #
# previous errors updating the domain. If errors are found, sends an email  #
# informing the owner that there are still unresolved errors from a         #
# previous attempt. If no errors are found, sends a POST request via curl   #
# to Google domains to update their dynamic DNS record with the system's    #
# new IP. Also emails owner the response from google for the latest POST    #
# request.                                                                  #
#                                                                           #
#                                                                           #
# Michael Rabinovsky        5-31-2017                                       #
# Special thanks to Wedge Jarrad                                            #
#############################################################################



##File Settings##

# Absolute path to the file which holds the current IP address.
# Updated via the ipcheck.sh script with the current IP just before executing this script.
ipfile="$HOME/.ipcheck.txt"

# Absolute path to the file which holds the old IP address.
# Used to check for errors from google.
previousipfile="$HOME/.previousip.txt"

# Absolute path to the file which should hold the responce from Google.
# Updated via the the curl command when running this script.
responsefile="$HOME/.ddnsresponse.txt"


##Email Settings##

# The email address that will serve as both the source and destination for
# emails sent by this script. It is also used as the username when
# authenticating with the smtp server.
email_address=""

# Password used to authenticate with the smtp server.
email_password=""

# SMTP server to use.
smtp_server=""

# SMTP server port. We will be connecting via TLS.
smtp_port=587

# Will appear in the email message. Useful if you have this script running from more than one box.
computer_name=""


##DNS Settings##

# The domain we want to update.
ddns_domain=""

# The DDNS user given to us by Google.
ddns_user=""

# the DDNS password given to us by Google.
ddns_password=""


##-----------------------##
#The part that does work!##

# Get the IP address, if any.
touch "$ipfile"
read -r ip < "$ipfile"

#Get the old IP, if any.
touch "$previousipfile"
read -r previousip < "$previousipfile"

# Stop now if we aren't able to retrieve valid IP addresses.
# Not a very robust IP regex but should be good enough to filter out error messages and such (by Wedge Jarrad).
[[ "$ip" =~ ^[0-9a-fA-F\.:]+$ ]] || exit 1
[[ "$previousip" =~ ^[0-9a-fA-F\.:]+$ ]] || exit 1

# Get the last response from google, if any.
touch "$responsefile"
read -r response < "$responsefile"

# Send an email informing owner that the last response was an error, and stop the script.
if [[ "$response" != "good $previousip" ]] && [[ "$response" != "nochg $previousip" ]]; then

        # RFC 2822 compliant SMTP email.
        email="ehlo localhost
        auth plain $(printf '\x00%s\x00%s' "$email_address" "$email_password" | base64)
        mail from: <$email_address>
        rcpt to: <$email_address>
        data
        from: $email_address
        subject: dynamic dns: $computer_name - pending error
        Google has responded with $response previously and the error was never cleared from the system.
        Nothing has been changed.
        The previous IP was $oldip. The new IP is $ip.
        .
        QUIT"

        slowly() {
            while read -r line; do
                sleep 1
                printf '%s\n' "$line"
            done <<< "$email"
        }

        slowly | openssl s_client -crlf -starttls smtp -connect "$smtp_server":"$smtp_port" > /dev/null 2>&1

        exit 1
fi

# Send the current IP address to Google.
# Update the response file with the response from google.
if [ command -v curl > /dev/null ]; then
    curl -L "https://$ddns_user:$ddns_password@domains.google.com/nic/update?hostname=$ddns_domain" > .ddnsresponse.txt
else
    # don't have curl. Bail out.
    printf '%s' "This script requires curl to be installed."
    exit 1

fi

# Get the last response from google, if any.
read -r response < "$responsefile"

# Email the response to owner.
# If response is anything other than a succesful IP change, send error email, else send success.
if [[ "$response" != "good $ip" ]]; then

        # RFC 2822 compliant SMTP error email.
        email="ehlo localhost
        auth plain $(printf '\x00%s\x00%s' "$email_address" "$email_password" | base64)
        mail from: <$email_address>
        rcpt to: <$email_address>
        data
        from: $email_address
        subject: dynamic dns: $computer_name - update error
        $computer_name has tried to update the DNS record for $ddns_domain and got an error.
        Google has responded with $response.
        The previous IP was $previousip. The new IP is $ip.
        .
        QUIT"
else
        # RFC 2822 compliant SMTP success email.
        email="ehlo localhost
        auth plain $(printf '\x00%s\x00%s' "$email_address" "$email_password" | base64)
        mail from: <$email_address>
        rcpt to: <$email_address>
        data
        from: $email_address
        subject: dynamic dns: $computer_name - update success!
        $computer_name has tried to update the DNS record for $ddns_domain and it was a total success.
        Google has responded with $response, which means that you are a baller, shot caller.
        The previous IP was $previousip. The new IP is $ip.
        .
        QUIT"

fi

slowly() {
            while read -r line; do
                sleep 1
                printf '%s\n' "$line"
            done <<< "$email"
        }

        slowly | openssl s_client -crlf -starttls smtp -connect "$smtp_server":"$smtp_port" > /dev/null 2>&1