"""Loopback-only ETag demo serving data.json from the current directory."""
import argparse
import hashlib
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
from pathlib import Path


class Handler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path != "/data.json":
            self.send_error(404)
            return
        try:
            body = Path("data.json").read_bytes()
        except OSError:
            self.send_error(404)
            return
        etag = '"' + hashlib.sha256(body).hexdigest() + '"'
        if self.headers.get("If-None-Match") == etag:
            self.send_response(304)
            self.send_header("ETag", etag)
            self.end_headers()
            return
        self.send_response(200)
        self.send_header("Content-Type", "application/json")
        self.send_header("Content-Length", str(len(body)))
        self.send_header("ETag", etag)
        self.end_headers()
        self.wfile.write(body)


def main():
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument("--port", type=int, default=8765)
    args = parser.parse_args()
    with ThreadingHTTPServer(("127.0.0.1", args.port), Handler) as server:
        print(f"http://127.0.0.1:{server.server_port}/data.json", flush=True)
        try:
            server.serve_forever()
        except KeyboardInterrupt:
            pass


if __name__ == "__main__":
    main()