#!/usr/bin/env python3
"""Build, serve and rebuild when sources change: python3 tools/serve.py [--port 8000]."""
import argparse, errno, http.server, pathlib, subprocess, sys, threading, time

ROOT = pathlib.Path(__file__).resolve().parent.parent
DIST = ROOT / 'dist'


class Handler(http.server.SimpleHTTPRequestHandler):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, directory=str(DIST), **kwargs)

    def end_headers(self):
        self.send_header('Cache-Control', 'no-store')
        super().end_headers()

    def log_message(self, format, *args):
        pass


def build(first=False):
    result = subprocess.run([sys.executable, str(ROOT / 'build.py')], cwd=ROOT,
                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT, text=True)
    if result.returncode:
        print('build failed:\n' + result.stdout, flush=True)
    elif first:
        print(result.stdout, end='', flush=True)
    else:
        print(time.strftime('rebuilt %H:%M:%S'), flush=True)


def mtimes():
    files = [ROOT / 'build.py', *(ROOT / 'src').rglob('*')]
    stamps = {}
    for path in files:
        try:
            if path.is_file(): stamps[path] = path.stat().st_mtime_ns
        except FileNotFoundError:
            pass
    return stamps


def watch(stopped, previous):
    while not stopped.wait(0.5):
        current = mtimes()
        if current != previous:
            previous = current
            build()


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--port', type=int, default=8000)
    args = parser.parse_args()
    if not 1 <= args.port <= 65525:
        parser.error('--port must be between 1 and 65525 (leaves room for ten retries)')
    previous = mtimes()
    build(first=True)
    if not (DIST / 'index.html').is_file():
        sys.exit('Cannot serve: dist/index.html does not exist. Fix the build and try again.')
    for port in range(args.port, args.port + 11):
        try:
            server = http.server.ThreadingHTTPServer(('127.0.0.1', port), Handler)
            break
        except OSError as error:
            if error.errno != errno.EADDRINUSE:
                sys.exit(f'Cannot serve on port {port}: {error}')
    else:
        sys.exit(f'Cannot serve: ports {args.port}-{args.port + 10} are all busy.')
    if port != args.port:
        print(f'Port {args.port} was busy; using {port}.', flush=True)
    print(f'Serving dist/ at http://localhost:{port}  (Ctrl+C to stop)', flush=True)
    stopped = threading.Event()
    threading.Thread(target=watch, args=(stopped, previous), daemon=True).start()
    try:
        with server:
            server.serve_forever()
    finally:
        stopped.set()


if __name__ == '__main__':
    try:
        main()
    except KeyboardInterrupt:
        print('\nServer stopped.', flush=True)