#!/usr/bin/env python3
"""Combine multiple video files into one file using FFmpeg.

Example:
    python helper_files/combine_videos.py output.mp4 video1.mp4 video2.mp4 video3.mp4
    python helper_files/combine_videos.py --output merged.mp4 --inputs video1.mp4 video2.mp4
"""

import argparse
import os
import subprocess
import sys
from pathlib import Path


def build_concat_list(input_files, list_path):
    with open(list_path, "w", encoding="utf-8") as f:
        for path in input_files:
            f.write(f"file '{os.path.abspath(path)}'\n")


def run_ffmpeg(cmd):
    print("Running:", " ".join(cmd))
    result = subprocess.run(cmd, capture_output=True, text=True)
    if result.returncode != 0:
        print(result.stdout)
        print(result.stderr)
        raise RuntimeError(f"FFmpeg failed with exit code {result.returncode}")
    print("✅ Finished successfully.")


def concat_videos_copy(input_files, output_path):
    list_path = Path(output_path).with_suffix(".concat.txt")
    build_concat_list(input_files, list_path)

    cmd = [
        "ffmpeg",
        "-y",
        "-f", "concat",
        "-safe", "0",
        "-i", str(list_path),
        "-c", "copy",
        str(output_path),
    ]
    run_ffmpeg(cmd)
    list_path.unlink(missing_ok=True)


def concat_videos_reencode(input_files, output_path):
    inputs = []
    filter_parts = []
    audio_parts = []

    for i, video_path in enumerate(input_files):
        inputs.extend(["-i", str(video_path)])
        # Use semicolons to separate different input streams in the filter graph
        filter_parts.append(f"[{i}:v]scale=trunc(iw/2)*2:trunc(ih/2)*2,setpts=PTS-STARTPTS[v{i}]")
        audio_parts.append(f"[{i}:a]aresample=async=1[a{i}]")

    # Correctly separate individual stream filters with semicolons
    filter_complex = f"{';'.join(filter_parts)};{';'.join(audio_parts)};"
    filter_complex += "".join(f"[v{i}][a{i}]" for i in range(len(input_files)))
    filter_complex += f"concat=n={len(input_files)}:v=1:a=1[outv][outa]"

    cmd = [
        "ffmpeg",
        "-y",
        *inputs,
        "-filter_complex", filter_complex,
        "-map", "[outv]",
        "-map", "[outa]",
        "-c:v", "libx264",
        "-crf", "18",         # High quality video
        "-preset", "slow",    # High efficiency
        "-c:a", "aac",
        "-b:a", "256k",       # High quality audio
        "-movflags", "+faststart",
        str(output_path),
    ]
    run_ffmpeg(cmd)


def merge_videos(input_files, output_path):
    input_files = [str(Path(p).expanduser().resolve()) for p in input_files]
    output_path = str(Path(output_path).expanduser().resolve())

    if len(input_files) < 2:
        raise ValueError("You need at least 2 video files to merge.")

    for path in input_files:
        if not os.path.exists(path):
            raise FileNotFoundError(f"File not found: {path}")

    output_dir = Path(output_path).parent
    output_dir.mkdir(parents=True, exist_ok=True)

    try:
        concat_videos_copy(input_files, output_path)
    except Exception as exc:
        print(f"Fast copy method failed: {exc}")
        print("Retrying with re-encode fallback...")
        concat_videos_reencode(input_files, output_path)


def main():
    parser = argparse.ArgumentParser(description="Join two or more video files together with FFmpeg.")
    parser.add_argument("output_file", help="Path to the merged output video")
    parser.add_argument("input_files", nargs="+", help="Two or more videos to concatenate")
    args = parser.parse_args()

    try:
        merge_videos(args.input_files, args.output_file)
        print(f"Merged video saved to: {args.output_file}")
    except Exception as exc:
        print(f"Error: {exc}")
        sys.exit(1)


if __name__ == "__main__":
    main()