"""On-demand H.264/AAC browser preview from a local MediaMTX substream."""
import json
import os
from pathlib import Path
import re
import shutil
import signal
import subprocess
import sys
from urllib.parse import quote


def main():
    name = os.environ.get('MTX_PATH', '')
    if not re.fullmatch(r'cam_[a-f0-9]{16}_compat', name):
        raise SystemExit('Invalid preview path')
    data = Path(sys.argv[1]).resolve()
    config = json.loads((data / 'mediamtx.yml').read_text(encoding='utf8'))
    original = name.removesuffix('_compat') + '_sub'
    if config['paths'].get(original, {}).get('source', 'publisher') == 'publisher':
        raise SystemExit('Camera is disabled')
    secret = next(u['pass'] for u in config['authInternalUsers'] if u['user'] == 'vision')
    base = 'rtsp://vision:' + quote(secret, safe='') + '@127.0.0.1:18554/'
    executable = shutil.which('ffmpeg')
    if not executable:
        raise SystemExit('Install FFmpeg to enable compatible preview')
    # A bounded 768x432 / 10 fps preview keeps six lenses practical on a small
    # computer. Original main/sub streams and recording retain their own codecs.
    command = [executable, '-hide_banner', '-loglevel', 'error', '-nostdin',
               '-threads', '1', '-filter_threads', '1', '-rtsp_transport', 'tcp',
               '-timeout', '15000000', '-i', base + original,
               '-map', '0:v:0', '-map', '0:a:0?', '-sn', '-dn',
               '-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', '-level:v', '3.1',
               '-pix_fmt', 'yuv420p', '-crf', '26', '-maxrate', '1100k',
               '-bufsize', '2200k', '-g', '20', '-keyint_min', '20', '-sc_threshold', '0',
               '-c:a', 'aac', '-ar', '48000', '-ac', '1', '-b:a', '48k',
               '-f', 'rtsp', '-rtsp_transport', 'tcp', base + name]
    process = subprocess.Popen(command, stdin=subprocess.DEVNULL, stdout=subprocess.DEVNULL,
                               stderr=subprocess.PIPE, text=True, errors='replace')

    def stop(_signum, _frame):
        if process.poll() is None:
            process.terminate()
            try:
                process.wait(timeout=5)
            except subprocess.TimeoutExpired:
                process.kill()

    signal.signal(signal.SIGTERM, stop)
    signal.signal(signal.SIGINT, stop)
    try:
        for line in process.stderr:
            # Never write connection credentials from FFmpeg diagnostics to logs.
            clean = re.sub(r'rtsp://[^\s]+', '[local stream]', line.replace(secret, '[redacted]'))
            print(name + ': ' + clean.rstrip(), file=sys.stderr, flush=True)
        return process.wait()
    finally:
        stop(None, None)


if __name__ == '__main__':
    sys.exit(main())