#!/usr/bin/env python3
"""Static dev server for the ATS dashboard.

Identical to `python3 -m http.server` except it disables caching. The stdlib
server answers conditional requests from Last-Modified, which has one-second
granularity — so a file edited twice within the same second keeps serving the
stale copy and the browser never sees the change.
"""
import sys
from functools import partial
from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer


class NoCacheHandler(SimpleHTTPRequestHandler):
    def end_headers(self):
        self.send_header("Cache-Control", "no-store, no-cache, must-revalidate, max-age=0")
        self.send_header("Pragma", "no-cache")
        self.send_header("Expires", "0")
        super().end_headers()

    def send_header(self, keyword, value):
        # Drop the validator entirely so conditional GETs can't 304.
        if keyword.lower() == "last-modified":
            return
        super().send_header(keyword, value)

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


if __name__ == "__main__":
    port = int(sys.argv[1]) if len(sys.argv) > 1 else 4173
    directory = sys.argv[2] if len(sys.argv) > 2 else "."
    handler = partial(NoCacheHandler, directory=directory)
    print(f"Serving {directory} on http://localhost:{port} (no-cache)")
    ThreadingHTTPServer(("127.0.0.1", port), handler).serve_forever()