#!/usr/bin/env python
"""Concatenate MP4 chunks by decoding and re-encoding with PyAV."""

from __future__ import annotations

import argparse
import json
from fractions import Fraction
from pathlib import Path

import av


def concat_videos(inputs: list[Path], output_path: Path, fps: float) -> int:
    if not inputs:
        raise ValueError("No input chunks to concatenate")

    first = av.open(str(inputs[0]))
    try:
        first_stream = first.streams.video[0]
        width = first_stream.width
        height = first_stream.height
    finally:
        first.close()

    output_path.parent.mkdir(parents=True, exist_ok=True)
    container = av.open(str(output_path), "w")
    success = False
    frame_count = 0
    try:
        output_fps = round(fps)
        time_base = Fraction(1, output_fps)
        stream = container.add_stream("libx264", rate=output_fps, options={"crf": "19", "preset": "veryfast"})
        stream.width = width
        stream.height = height
        stream.pix_fmt = "yuv420p"
        stream.time_base = time_base
        stream.codec_context.thread_count = 0
        stream.codec_context.thread_type = "FRAME"

        for input_path in inputs:
            chunk = av.open(str(input_path))
            try:
                video_stream = chunk.streams.video[0]
                if video_stream.width != width or video_stream.height != height:
                    raise ValueError(
                        f"Chunk {input_path} is {video_stream.width}x{video_stream.height}, "
                        f"expected {width}x{height}"
                    )
                for frame in chunk.decode(video_stream):
                    frame = frame.reformat(width=width, height=height, format="yuv420p")
                    frame.pts = frame_count
                    frame.time_base = time_base
                    for packet in stream.encode(frame):
                        container.mux(packet)
                    frame_count += 1
            finally:
                chunk.close()

        for packet in stream.encode():
            container.mux(packet)
        success = True
    finally:
        container.close()
        if not success:
            output_path.unlink(missing_ok=True)
    return frame_count


def main() -> None:
    parser = argparse.ArgumentParser()
    parser.add_argument("--output", required=True)
    parser.add_argument("--fps", type=float, required=True)
    parser.add_argument("inputs", nargs="+")
    args = parser.parse_args()

    frames = concat_videos([Path(p) for p in args.inputs], Path(args.output), args.fps)
    print(json.dumps({"frames": frames}))


if __name__ == "__main__":
    main()