#!/usr/bin/env bash

# Usage example:
#   ./ffmpeg-join-videos.sh -i vid1.mp4 vid2.mp4 vid3.mp4 -o output_name

# Exit on error
set -e

# Parse arguments
videos=()
output_filename=""

while [[ $# -gt 0 ]]; do
  case "$1" in
  -i | --input-list)
    shift
    # Collect all filenames until another option appears or args end
    while [[ $# -gt 0 && "$1" != -* ]]; do
      videos+=("$1")
      shift
    done
    ;;
  -o | --output-filename)
    output_filename="$2"
    shift 2
    ;;
  -h | --help)
    echo "Usage: $0 -i file1 file2 [file3 ...] -o output_name"
    exit 0
    ;;
  *)
    echo "Unknown option: $1"
    exit 1
    ;;
  esac
done

# Validate args
if [[ ${#videos[@]} -lt 2 ]]; then
  echo "Error: You must provide at least two input files with -i"
  exit 1
fi

if [[ -z "$output_filename" ]]; then
  echo "Error: You must provide an output filename with -o"
  exit 1
fi

# Number of videos
n=${#videos[@]}

# Build input args for ffmpeg
inputs=()
for vid in "${videos[@]}"; do
  inputs+=("-i" "$vid")
done

# Build the concat filter
filter=""
for i in "${!videos[@]}"; do
  filter+="[$i:v] [$i:a] "
done

filter_complex="${filter}concat=n=$n:v=1:a=1 [v] [a]"

# Run ffmpeg
ffmpeg "${inputs[@]}" -filter_complex "$filter_complex" -map "[v]" -map "[a]" "${output_filename}.mp4"