#!/bin/bash

if [ $# -ne 2 ]; then
    echo "Usage: `basename $0` SRTFILE DELAY"
    echo "Parameters (required):"
    echo -e "\tSTRFILE\t .srt file to read"
    echo -e "\tDELAY\t delay to add/subtract, in whole miliseconds"
    echo "The new file is sent to stdout."
    exit
fi

if [ ! -r $1 ]; then
    echo "No file given."
    exit
fi

FILE=$1
ADD=$2
PART='([0-9][0-9]):([0-9][0-9]):([0-9][0-9]),([0-9][0-9][0-9])'
RE="^$PART --> $PART$"

add() {
    XADDED=$(( $4+$ADD ))
    XNEW=`printf "%.3d" $(( $XADDED%1000 ))`
    SADDED=$(( $3+($XADDED/1000) ))
    SNEW=`printf "%.2d" $(( $SADDED%60 ))`
    MADDED=$(( $2+($SADDED/60) ))
    MNEW=`printf "%.2d" $(( $MADDED%60 ))`
    HNEW=`printf "%.2d" $(( $1+($MADDED/60) ))`
    NEW="$HNEW:$MNEW:$SNEW,$XNEW"
    echo $NEW
}

while read LINE
do
    TEST=`egrep -ro "$RE" <<< "$LINE"`
    if [ -n "$TEST" ]; then
        H=`echo $LINE | sed -re "s/$RE/\1/"`
        M=`echo $LINE | sed -re "s/$RE/\2/"`
        S=`echo $LINE | sed -re "s/$RE/\3/"`
        X=`echo $LINE | sed -re "s/$RE/\4/"`
        START=`add $H $M $S $X`
        H=`echo $LINE | sed -re "s/$RE/\5/"`
        M=`echo $LINE | sed -re "s/$RE/\6/"`
        S=`echo $LINE | sed -re "s/$RE/\7/"`
        X=`echo $LINE | sed -re "s/$RE/\8/"`
        END=`add $H $M $S $X`
        echo "$START --> $END"
    else
        echo "$LINE"
    fi
done < $FILE