#!/bin/bash

readonly USAGE="
USAGE:
$(basename "$0") [FILE]"

function help_message() {
    echo "$USAGE"
}

# check if there is any parameter
if [ "$#" -ne 1 ]; then
    help_message
    exit 0
fi

# check if the parameter is valid
if ! test -f "$1"; then
    echo "File $1 does not exist."
    exit 0
fi

# variables
readonly FILE_DIR="$(cd "$(dirname "$1")" && pwd)"
readonly FILE="$(basename "$1")"

OLD_DATE="$(date -r "$1" "+%Y-%m-%d_%H:%M:%S")"
cp "${FILE_DIR}/${FILE}" "${FILE_DIR}/${FILE}.${OLD_DATE}"
if ! test -f "${FILE_DIR}/${FILE}.tar"; then
    tar -C "${FILE_DIR}" -cf "${FILE_DIR}/${FILE}.tar" "${FILE}.${OLD_DATE}"
    echo "File ${FILE}.tar created."
    echo "${FILE}.${OLD_DATE}"
else
    tar -C "${FILE_DIR}" -rf "${FILE_DIR}/${FILE}.tar" "${FILE}.${OLD_DATE}"
    echo "${FILE}.${OLD_DATE}"
fi
rm "${FILE_DIR}/${FILE}.${OLD_DATE}"

while true; do
    sleep 5
    DATE="$(date -r "$1" "+%Y-%m-%d_%H:%M:%S")"
    if [ "$DATE" != "$OLD_DATE" ]; then
        echo "${FILE}.${DATE}"
        cp "${FILE_DIR}/${FILE}" "${FILE_DIR}/${FILE}.${DATE}"
        tar -C "${FILE_DIR}" -rf "${FILE_DIR}/${FILE}.tar" "${FILE}.${DATE}"
        rm "${FILE_DIR}/${FILE}.${DATE}"
        OLD_DATE=$DATE
    fi
done