#!/bin/bash

### I lost the link where I copied this script from, sorry, i'll update as soon as I find it back!

## This scripts checks for the last succesful BORG backups of a HOST, and alerts ntfy in case no succesful backup has been created for the last X days

backup_host="HOST_NAME"
n_days=3                  # if backup was less recent than n_days, alert administrator 
topicurl=https://NTFY_SERVER_IP/borg_alerts
make_it_fail=0                  # set to 1 to test your alerts by simulating an old backup 

export BORG_REPO=/mnt/BORG/$backup_host # point to your borg repo 
export BORG_REMOTE_PATH=/usr/bin/borg # point to your borg executable 
#export BORG_PASSPHRASE='redacted'

die()
{
    echo "Error fetching or calculating date"
    curl -k --retry 3 \
    -d "Error fetching or calculating date" \
    -H "Title: Borg on $backup_host" \
    -H "Priority: high" \
    -H "Tags: warning,boar" \
    $topicurl
    exit 1
}

is_num()                        # returns (exits) 0 if passed a valid integer
{
    if (( $1 == $1 )) 2>/dev/null; then 
        return 0
    else
        return 1
    fi
}

last=`borg list --last 10 --format "{archive} {end} {NEWLINE}" | grep --invert-match checkpoint | tail -1` # get the last 10 backups from the repo, filter out checkpoints, get last one

if (( $make_it_fail )); then
    last="qwho-1989-05-08T11:11:11 Thu, 1989-05-08 11:11:11" # simulate an old backup
fi

echo Last backup: $last

last_date=$( echo $last | cut -d " " -f 3 )
if [[ -z $last_date ]]; then
   die                          # didn't get a string
fi

last_timestamp=$( date --date=$last_date +%s 2>/dev/null ) 
now_timestamp=$( date +%s )
if ! ( ( is_num $last_timestamp ) && ( is_num $now_timestamp ) ); then
    die                         # invalid timestamp 
fi

days_ago=$( echo "($now_timestamp - $last_timestamp) / (3600 * 24)" | bc )
if ! ( ( is_num $days_ago ) && (( $days_ago >= 0 )) ); then
    die                         # invalid or negative result 
fi

# Sums successful - check backup time and send appropriate ntfy alert
if (( $days_ago < $n_days )); then
    echo Good - last backup was $days_ago days ago - less than the $n_days day limit 
    echo Not sending alert to ntfy server...
else
    echo Bad - last backup was $days_ago days ago - greater than the $n_days day limit
    echo Sending alert...
    curl -k --retry 3 \
    -d "Bad - last backup was $days_ago days ago - greater than the $n_days day limit" \
    -H "Title: Borg on $backup_host" \
    -H "Priority: high" \
    -H "Tags: warning,boar" \
    $topicurl
fi