import sys
import subprocess

def combine_videos_with_music(videos, music_file, output_file="output.mp4"):
    if len(videos) < 2:
        print("Please provide at least two video files.")
        sys.exit(1)

    if not music_file:
        print("Please provide a background music file.")
        sys.exit(1)

    # Construct ffmpeg input arguments
    input_args = []
    for video in videos:
        input_args.extend(["-i", video])
    input_args.extend(["-i", music_file])  # background music

    # Build filter_complex string
    concat_count = len(videos)
    video_inputs = "".join([f"[{i}:v:0]" for i in range(concat_count)])
    filter_complex = f"{video_inputs}concat=n={concat_count}:v=1:a=0[v]"

    # Final ffmpeg command
    cmd = [
        "ffmpeg",
        *input_args,
        "-filter_complex", filter_complex,
        "-map", "[v]",
        "-map", f"{concat_count}:a",  # use bg.mp3 as audio
        "-shortest",
        "-y",
        output_file
    ]

    # Run ffmpeg
    subprocess.run(cmd)

if __name__ == "__main__":
    if len(sys.argv) < 4:
        print("Usage: python combine_videos_with_music.py v1.mp4 v2.mp4 v3.mp4 bg.mp3")
        sys.exit(1)

    *video_files, bg_music = sys.argv[1:]
    combine_videos_with_music(video_files, bg_music)