"""Bounded, ephemeral H.264 playback; original recordings remain untouched."""
from contextlib import contextmanager
import os
import shutil
import subprocess
import threading

SLOTS = threading.BoundedSemaphore(2)


class PlaybackError(Exception):
    pass


def command(source, authorization, duration):
    executable = shutil.which('ffmpeg')
    if not executable:
        raise PlaybackError('回放转换需要服务器安装 FFmpeg')
    device = os.environ.get('VISION_VAAPI_DEVICE', '/dev/dri/renderD128')
    acceleration = []
    if os.access(device, os.R_OK | os.W_OK):
        acceleration = ['-hwaccel', 'vaapi', '-hwaccel_device', device,
                        '-hwaccel_output_format', 'vaapi', '-extra_hw_frames', '8']
        video = ['-vf', 'fps=15,scale_vaapi=w=1920:h=1080:format=nv12:force_original_aspect_ratio=decrease:force_divisible_by=2',
                 '-c:v', 'h264_vaapi', '-profile:v', 'main', '-level:v', '4.1',
                 '-rc_mode', 'CQP', '-qp', '25', '-g', '30', '-bf', '0']
    else:
        video = ['-vf', 'fps=10,scale=768:432:force_original_aspect_ratio=decrease:force_divisible_by=2',
                 '-c:v', 'libx264', '-threads', '1', '-preset', 'veryfast',
                 '-tune', 'zerolatency', '-profile:v', 'baseline', '-pix_fmt', 'yuv420p',
                 '-crf', '26', '-g', '20', '-bf', '0']
    return [executable, '-hide_banner', '-loglevel', 'error', '-nostdin',
            '-threads', '1', '-filter_threads', '1'] + acceleration + [
            '-rw_timeout', '15000000', '-headers', 'Authorization: ' + authorization + '\r\n',
            '-readrate', '1', '-i', source, '-t', str(duration),
            '-map', '0:v:0', '-map', '0:a:0?', '-sn', '-dn'] + video + [
            '-c:a', 'aac', '-ar', '48000', '-ac', '1', '-b:a', '64k',
            '-movflags', '+frag_keyframe+empty_moov+default_base_moof',
            '-frag_duration', '1000000', '-f', 'mp4', 'pipe:1']


@contextmanager
def stream(source, authorization, duration):
    if not SLOTS.acquire(blocking=False):
        raise PlaybackError('已有两个回放正在进行，请关闭其他回放后重试')
    process = timer = None
    try:
        # No shell and no diagnostics containing authentication headers in logs.
        process = subprocess.Popen(command(source, authorization, duration),
                                   stdin=subprocess.DEVNULL, stdout=subprocess.PIPE,
                                   stderr=subprocess.DEVNULL)
        timer = threading.Timer(duration + 45, process.kill)
        timer.daemon = True
        timer.start()
        yield process.stdout
    except OSError as exc:
        raise PlaybackError('录像转换服务暂不可用') from exc
    finally:
        if timer:
            timer.cancel()
        if process:
            if process.poll() is None:
                process.terminate()
                try:
                    process.wait(timeout=3)
                except subprocess.TimeoutExpired:
                    process.kill()
                    process.wait()
            process.stdout.close()
        SLOTS.release()