#!/bin/bash

GREEN_FG="\033[32m"
RED_FG="\033[31m"
NORMAL="\033[0m"

TM_RESULTS="/private/var/db/.TimeMachine.Results"

if [ ! -f "${TM_RESULTS}.plist" ]; then
    echo -e "${RED_FG}No successful backup (is it currently in progress?)${NORMAL}"
    exit
fi
# timestamp when backup was completed (in UTC +0000)
backup_date=$(defaults read ${TM_RESULTS} BACKUP_COMPLETED_DATE 2>/dev/null)
if [ $? -ne 0 ]; then
    echo -e "${RED_FG}No successful backup${NORMAL}"
    exit
fi
# convert time machine timestamp to epoch seconds
#   -j do not try to set the date
#   -f format string
epoch_tm_completed=$(date -jf "%F %T %z" "$(echo $backup_date)" +%s)
# convert now to epoch seconds
epoch_now=$(date +%s)

function duration_in_words() {
    # difference in seconds
    local seconds_ago=$(($1 - $2))
    # difference in minutes
    local minutes_ago=$((seconds_ago / 60))
    if [ $minutes_ago = 0 ]; then
        echo "less than a minute" && return
    fi
    if [ $minutes_ago = 1 ]; then
        echo "a minute" && return
    fi
    if [ $minutes_ago -lt 45 ]; then
        echo "$minutes_ago minutes" && return
    fi
    if [ $minutes_ago -lt 90 ]; then
        echo "about 1 hour" && return
    fi
    # difference in hours
    local hours_ago=$((minutes_ago / 60))
    if [ $minutes_ago -lt 1440 ]; then
        echo "about $hours_ago hours" && return
    fi
    if [ $minutes_ago -lt 2880 ]; then
        echo "1 day" && return
    fi
    # difference in days
    local days_ago=$((minutes_ago / 1440))
    if [ $minutes_ago -lt 43200 ]; then
        echo "$days_ago days" && return
    fi
    if [ $minutes_ago -lt 86400 ]; then
        echo "about 1 month" && return
    fi
    # difference in months
    local months_ago=$((minutes_ago / 43200))
    if [ $minutes_ago -lt 525960 ]; then
        echo "about $months_ago months" && return
    fi
    if [ $minutes_ago -lt 1051920 ]; then
        echo "about 1 year" && return
    fi
    # difference in years
    local years_ago=$((minutes_ago / 525960))
    echo "over $years_ago years"
}

# get 2 lines back and store them in the duration array
duration=( $(grep 'com.apple.backupd' /var/log/system.log | \
    awk '
                # initialize buffer and flag when start text is found
/Starting (manual|automatic) backup/   { a=""; f=0 }
                # accumulate in buffer while in-between start and end text
/Starting (manual|automatic) backup/,/Backup completed successfully/   {
    if (a == "") a = $0
}
                # store first line in secondary buffer when end text is found (to
                # cover the case where end text is never found after start text)
!f && /Backup completed successfully/  { b=a; f=1; last=$0 }
                # print portion of correct buffer based on flag for first line
                # print portion of last line
END { print substr(f ? a : b, 8, 8); print substr(last, 8, 8) }
') )

# convert start of backup to epoch seconds
epoch_tm_start=$(date -jf "%T" ${duration[0]} +%s)
# convert end of backup to epoch seconds
epoch_tm_end=$(date -jf "%T" ${duration[1]} +%s)

echo -e "Successful backup${GREEN_FG}" \
    $(duration_in_words $epoch_now $epoch_tm_completed) \
    "ago${NORMAL} in${GREEN_FG}" \
    $(duration_in_words $epoch_tm_end $epoch_tm_start) \
    "${NORMAL}"