#!/usr/bin/env python3
"""Static server for the alias-web bundle, with HTTP Range support for the 2.4 GB weight file.

    python3 serve.py [port]        # default 8924; then open http://127.0.0.1:<port> in Chrome or Edge

Binds to 127.0.0.1 only. Responses are marked no-store so that a changed module is never served stale;
CORS is open so that a local browser extension can fetch the model from this server.
"""
import http.server, os, re, socketserver, sys

ROOT = os.path.dirname(os.path.abspath(__file__))


class Handler(http.server.SimpleHTTPRequestHandler):
    def __init__(self, *a, **kw):
        super().__init__(*a, directory=ROOT, **kw)

    def send_head(self):
        self._remaining = None
        path = self.translate_path(self.path)
        rng = self.headers.get("Range")
        if not rng or not os.path.isfile(path):
            return super().send_head()
        size = os.path.getsize(path)
        m = re.match(r"bytes=(\d*)-(\d*)$", rng.strip())
        if not m or not (m.group(1) or m.group(2)):
            self.send_error(416)
            return None
        if m.group(1):
            start, end = int(m.group(1)), min(int(m.group(2)) if m.group(2) else size - 1, size - 1)
        else:  # suffix form: the last N bytes
            start, end = max(0, size - int(m.group(2))), size - 1
        if start > end:
            self.send_error(416)
            return None
        f = open(path, "rb")
        f.seek(start)
        self._remaining = end - start + 1
        self.send_response(206)
        self.send_header("Content-Type", self.guess_type(path))
        self.send_header("Content-Range", f"bytes {start}-{end}/{size}")
        self.send_header("Content-Length", str(self._remaining))
        self.end_headers()
        return f

    def copyfile(self, source, outputfile):
        if self._remaining is None:
            return super().copyfile(source, outputfile)
        left = self._remaining
        while left > 0:
            chunk = source.read(min(1 << 20, left))
            if not chunk:
                break
            outputfile.write(chunk)
            left -= len(chunk)

    def end_headers(self):
        self.send_header("Accept-Ranges", "bytes")
        self.send_header("Cache-Control", "no-store")
        self.send_header("Access-Control-Allow-Origin", "*")
        super().end_headers()


socketserver.TCPServer.allow_reuse_address = True
if __name__ == "__main__":
    port = int(sys.argv[1]) if len(sys.argv) > 1 else 8924
    with socketserver.ThreadingTCPServer(("127.0.0.1", port), Handler) as s:
        print(f"serving {ROOT} on http://127.0.0.1:{port}")
        s.serve_forever()