#!/usr/bin/env python3
"""Offline beat detection for a rendered/generated audio track.

Usage:
    python beat_detect.py <audio_path>

Prints a single JSON object to stdout:
    {"tempo": <bpm float>, "beats": [<seconds float>, ...], "duration": <seconds float>}

Local/offline only: librosa + numpy (already pinned for the asset venv). No network, no model
downloads. On any failure it prints {"tempo": 0, "beats": [], "duration": 0} and exits 0 so the
caller can fail soft to un-synced cuts rather than failing the render.
"""
import json
import sys


def main() -> int:
    if len(sys.argv) < 2:
        print(json.dumps({"tempo": 0, "beats": [], "duration": 0}))
        return 0
    audio_path = sys.argv[1]
    try:
        import librosa

        # sr=None keeps the file's native rate; mono is enough for beat tracking.
        y, sr = librosa.load(audio_path, sr=None, mono=True)
        duration = float(librosa.get_duration(y=y, sr=sr))
        tempo, beat_frames = librosa.beat.beat_track(y=y, sr=sr, units="frames")
        beat_times = librosa.frames_to_time(beat_frames, sr=sr)
        beats = [round(float(t), 4) for t in beat_times.tolist()]
        tempo_val = float(tempo[0]) if hasattr(tempo, "__len__") else float(tempo)
        print(json.dumps({"tempo": round(tempo_val, 2), "beats": beats,
                          "duration": round(duration, 4)}))
        return 0
    except Exception as exc:  # noqa: BLE001 - fail soft, never break the render
        sys.stderr.write("beat_detect failed: %s\n" % exc)
        print(json.dumps({"tempo": 0, "beats": [], "duration": 0}))
        return 0


if __name__ == "__main__":
    raise SystemExit(main())