#! /bin/bash

IFS=$'\n'
option_F_found=0
option_T_found=0

usage()
{
echo "usage: ./subtitles.sh -f [srt file] -t '[+/- time]'"
echo "ex : ./subtitles.sh -f /home/std/lecuisinierlevoleursafemmeetsonamant.srt -t '- 18.100'"
echo "ex : ./subtitles.sh -f /home/std/lecuisinierlevoleursafemmeetsonamant.srt -t '+ 18.100'"
echo ""
exit 3
}

while getopts f:t: OPTNAME; do
case "$OPTNAME" in
f)
FILE="$OPTARG"
option_F_found=1
;;

t)
TIME="$OPTARG"
option_T_found=1
;;

*)
usage
;;
esac
done

if [ "$option_F_found" -eq "0" ] || [ "$option_T_found" -eq "0" ]; then
usage
fi

FunctionDuration()
{
duration_temp=$(date -d "1983-12-12 $1" "+%s.%3N")
duration_diff=$(echo "scale=3; $duration_temp $TIME" | bc -l)
duration_dest=$(date -d"@$duration_diff" "+%H:%M:%S,%3N")
echo "$duration_dest"
}

for i in $(grep -E "[0-9]{2}:[0-9]{2}\,[0-9]{3}" "$FILE");
do
A=$(echo "$i" | sed 's/\([0-9]\{2\}:[0-9]\{2\}:[0-9]\{2\}\,[0-9]\{3\}\) --> \([0-9]\{2\}:[0-9]\{2\}:[0-9]\{2\}\,[0-9]\{3\}\)/\1/')
B=$(echo "$i" | sed 's/\([0-9]\{2\}:[0-9]\{2\}:[0-9]\{2\}\,[0-9]\{3\}\) --> \([0-9]\{2\}:[0-9]\{2\}:[0-9]\{2\}\,[0-9]\{3\}\)/\2/')
VAL1=$(FunctionDuration "$A")
VAL2=$(FunctionDuration "$B")
echo "working on $A --> $B"
sed -i "s/$i/$VAL1 --> $VAL2/" "$FILE"
done