#!/usr/bin/env python3
"""Static file server for the rendered Bible site.

Stdlib only, so the container needs nothing but a Python base image. Its one
job beyond serving files is getting cache headers right: the service worker
owns the offline copy, and if the worker or the pages that register it are
served stale, a new build can never reach a device that already installed the
old one.

Expects to sit behind something that terminates TLS. That is not optional for
the offline app: browsers only register a service worker in a secure context,
so a device loading this over plain http:// from a LAN address installs the
page but never gets an offline copy.
"""

from __future__ import annotations

import argparse
import os
import signal
import sys
from functools import partial
from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer

# Revalidate every time: these are what carry an update to an installed app.
NO_CACHE_NAMES = {"sw.js"}
NO_CACHE_EXTS = {".html", ".webmanifest"}


class Handler(SimpleHTTPRequestHandler):
    extensions_map = {
        **SimpleHTTPRequestHandler.extensions_map,
        ".html": "text/html; charset=utf-8",
        ".css": "text/css; charset=utf-8",
        ".js": "text/javascript; charset=utf-8",
        ".json": "application/json; charset=utf-8",
        ".webmanifest": "application/manifest+json; charset=utf-8",
        ".png": "image/png",
        ".svg": "image/svg+xml",
    }
    server_version = "bible-static"
    sys_version = ""

    def end_headers(self):
        path = self.path.split("?", 1)[0]
        name = os.path.basename(path)
        ext = os.path.splitext(name)[1].lower()
        if name in NO_CACHE_NAMES or ext in NO_CACHE_EXTS or path.endswith("/"):
            self.send_header("Cache-Control", "no-cache")
        else:
            self.send_header("Cache-Control", "public, max-age=604800")
        # Lets the worker claim the whole origin even if it moves off root.
        self.send_header("Service-Worker-Allowed", "/")
        self.send_header("X-Content-Type-Options", "nosniff")
        super().end_headers()

    def log_message(self, fmt, *args):
        sys.stdout.write("%s %s\n" % (self.address_string(), fmt % args))
        sys.stdout.flush()


def main(argv=None):
    ap = argparse.ArgumentParser(description=__doc__,
                                 formatter_class=argparse.RawDescriptionHelpFormatter)
    ap.add_argument("--root", default=os.environ.get("SITE_ROOT", "books"),
                    help="directory to serve (default: books)")
    ap.add_argument("--host", default=os.environ.get("HOST", "0.0.0.0"))
    ap.add_argument("--port", type=int, default=int(os.environ.get("PORT", "8080")))
    args = ap.parse_args(argv)

    root = os.path.abspath(args.root)
    if not os.path.isdir(root):
        sys.exit("site root not found: %s" % root)

    httpd = ThreadingHTTPServer((args.host, args.port),
                                partial(Handler, directory=root))
    httpd.daemon_threads = True

    def stop(_signum, _frame):
        httpd.shutdown()

    signal.signal(signal.SIGTERM, stop)
    signal.signal(signal.SIGINT, stop)

    print("serving %s at http://%s:%d" % (root, args.host, args.port))
    sys.stdout.flush()
    try:
        httpd.serve_forever()
    finally:
        httpd.server_close()
    return 0


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