#!/bin/bash
usage(){
  cat << EOF

 $(basename $0) -a <accelerate> -b bitrate -d <directory> -p <prefix> -q -v <video_dir> -s <size>

 ——————————————————————————————————————————————————————————————————————————————————
 Opt | Variable      | Type  | Definition                           | Default value
 ——————————————————————————————————————————————————————————————————————————————————
 -a    accelerate      int     Convert only 1/N images                1
 -b    bitrate         str     Video bitrate                          1500k 
 -d    directory       path    Directory path of images to convert    ./pics
 -p    prefix          str     Images filename prefix.                ''
 -q    quiet           int     Minimal output                         0
 -v    video_dir       path    Directory path to store video file.    ./videos
 -s    size            str     Images geometry.                       '1024x768'
 ——————————————————————————————————————————————————————————————————————————————————

EOF
  exit
}
panic(){ echo $@; exit 2;}

directory="./pics"
prefix=""
accelerate="1"
size='1024x768'
video_dir="./videos"
bitrate="1500k"
quiet=0

while getopts "a:b:d:hs:p:qr:v:" o; do
  case "${o}" in
    a)
      accelerate=${OPTARG}
    ;;
    b)
      bitrate=${OPTARG}
    ;;
    d)
      directory=${OPTARG}
    ;;
    h)
      usage
    ;;
    p)
      prefix=${OPTARG}
    ;;
    q)
      quiet=1
    ;;
    s)
      size=${OPTARG}
    ;;
    v)
      video_dir=${OPTARG}
    ;;
    \?)
      panic "Unknown option at position $OPTIND. Exiting."
    ;;
  esac
done

# Safe test ffmpeg
which ffmpeg &>/dev/null || panic "No ffmpeg found. Exiting."

# Safe test directory
directory="$( realpath ${directory} 2>/dev/null )/"
[ -n "${directory}" ] && [ -d "${directory}" ] || panic "'${directory}' is not a valid directory. Exiting."

# Safe test accelerate
[ ${accelerate} -gt 0 ] || panic "Invalid rate '${rate}'"

# Safe test prefix
let c=0
tmpfile=$( mktemp )
for file in ${directory}${prefix}* ; do 

    let $(( c++ ))
    [[ $(( $c % ${accelerate} )) -eq 0 ]] || [[ $rate -eq 1 ]] && echo "file '$file'" >> $tmpfile

done

[ 0 -eq $c ] && panic "No file found"


# Safe test video_dir
video_dir="$( realpath ${video_dir} 2>/dev/null )/"
[ -n "${video_dir}" ] || panic "The video_dir option cannot be empty. Exiting."
[ -d "${video_dir}" ] || {
  read -p "'${video_dir}' does not exist, do you want to create it? [Y/n] : "
  REPLY=${REPLY:-Y}
  [ "N" == ${REPLY^^} ] && panic "The video directory must exist. Exiting."
  mkdir -p ${video_dir} 2>/dev/null || panic "Failed to create '${video_dir}'. Exiting"
}

# Set video file name
date=$(date +%s)
video_file="${video_dir}$date.mp4"
echo -e "\nSaving to video file $video_file\n"

[ 0 -eq $quiet ] || quiet_options=" -hide_banner -loglevel quiet -stats "
ffmpeg $quiet_options -f concat -safe 0 -i "${tmpfile}" -pix_fmt yuv420p -s "${size}"  -vcodec libx264 -b ${bitrate} "${video_file}"
rm -f $tmpfile