#!/bin/bash
CUTINTO=$3
SOURCE=$1
OUTPUT=$2
SKIPFRAME=$4
FRAMES=$(ffprobe -v error -count_frames -select_streams v:0 -show_entries stream=nb_read_frames -of default=nokey=1:noprint_wrappers=1 $SOURCE)
WIDTH=$(ffprobe -v error -select_streams v:0 -show_entries stream=width -of default=nokey=1:noprint_wrappers=1 $SOURCE)
HEIGHT=$(ffprobe -v error -select_streams v:0 -show_entries stream=height -of default=nokey=1:noprint_wrappers=1 $SOURCE)
VERT=$5
ORD=$6
if [ "$VERT" == "vertical" ];
then
    CUT=$((WIDTH/CUTINTO))
else
    CUT=$((HEIGHT/CUTINTO))
fi
echo "cut is $CUT"

i=0
N=4
j=0
while [ "$i" -lt "$CUTINTO" ];
do
    if [ "$ORD" == "normal" ];
    then
        STARTTIME=$((SKIPFRAME*i))
    else
        STARTTIME=$((SKIPFRAME*(CUTINTO-i-1)))
    fi
    START=$((CUT*i))
    ENDTIME=$((FRAMES-(CUTINTO-1)*SKIPFRAME+STARTTIME))
    echo "$STARTTIME $ENDTIME"
    ((j=j%N)); ((j++==0)) && wait
    if [ "$VERT" == "vertical" ];
    then
        ffmpeg -loglevel error -i $SOURCE -an -vf "crop=$CUT:$HEIGHT:$START:0, trim=end_frame=$ENDTIME, trim=start_frame=$STARTTIME" tmp$i.mp4 &
    else
        ffmpeg -loglevel error -i $SOURCE -an -vf "crop=$WIDTH:$CUT:0:$START, trim=end_frame=$ENDTIME, trim=start_frame=$STARTTIME" tmp$i.mp4 &
    fi
    i=$((i+1))
done
wait
ls

function merge {
    from=$1
    to=$2
    if [ "$from" -eq "$to" ];
    then
        echo "tmp$from.mp4" 1>&2
        echo "tmp$from.mp4"
    else
        mid1=$(((from+to)/2))
        mid2=$((mid1+1))
        m1="$(merge $from $mid1)"
        m2="$(merge $mid2 $to)"
        echo "$m1 $m2" 1>&2
        out="t$m1"
        if [ "$VERT" == "vertical" ];
        then
            ffmpeg -i $m1 -i $m2 -an -loglevel error -filter_complex "[0:v][1:v]hstack" $out
        else
            ffmpeg -i $m1 -i $m2 -an -loglevel error -filter_complex "[0:v][1:v]vstack" $out
        fi
        mv $out $m1
        rm $m2
        echo $m1
    fi
}

merge 0 $((CUTINTO-1))
mv tmp0.mp4 $OUTPUT