"""Read action playback boundaries from the presentation timestamps of a final video."""

import json
import math
import subprocess


def frame_times(video_path):
    result = subprocess.run(
        ["ffprobe", "-v", "error", "-select_streams", "v:0", "-show_frames",
         "-show_entries", "frame=best_effort_timestamp_time,duration_time,pkt_duration_time",
         "-of", "json", str(video_path)],
        check=True, capture_output=True, text=True,
    )
    frames = json.loads(result.stdout).get("frames", [])
    try:
        times = [float(frame["best_effort_timestamp_time"]) for frame in frames]
    except (KeyError, TypeError, ValueError) as error:
        raise ValueError(f"Missing video frame timestamps: {video_path}") from error
    if not times or not all(math.isfinite(value) and value >= 0 for value in times):
        raise ValueError(f"Invalid video frame timestamps: {video_path}")
    if any(after <= before for before, after in zip(times, times[1:])):
        raise ValueError(f"Non-increasing video frame timestamps: {video_path}")
    last = frames[-1]
    duration = last.get("duration_time") or last.get("pkt_duration_time")
    duration = float(duration) if duration is not None else 0
    if duration <= 0 and len(times) > 1:
        duration = times[-1] - times[-2]
    if not math.isfinite(duration) or duration <= 0:
        raise ValueError(f"Missing final frame duration: {video_path}")
    return times + [times[-1] + duration]


def action_times(boundaries, start_frame, end_frame):
    if start_frame < 0 or end_frame < start_frame or end_frame + 1 >= len(boundaries):
        raise ValueError(f"Action frame range {start_frame}-{end_frame} is outside video")
    return {"start_time_seconds": boundaries[start_frame],
            "end_time_seconds": boundaries[end_frame + 1]}