#!/usr/bin/env python3
"""Static file server with HTTP Range support, for the OpenRA3 wasm build.

Emscripten's lazy file reads stream assets back as byte ranges, so the server
must honour the ``Range`` header -- Python's stdlib ``http.server`` does not.

    python3 apps/web/serve.py --root build/wasm/bin --port 8199
    # then open http://localhost:8199/index.html

Serve ``--root`` containing ``index.html``, ``openra3.js``, ``openra3.wasm``,
``openra3.worker.js`` and ``assets.manifest.json``. The lazy asset tree is
mounted from ``--assets`` (its files are then fetched from ``/assets/<rel>`` on
demand); without ``--assets`` the tree is expected under ``--root`` itself.
"""

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

_RANGE = re.compile(r"bytes=(\d*)-(\d*)$")


class RangeHandler(SimpleHTTPRequestHandler):
    # Directory served for ``/assets/...`` (set in main); None means "under root".
    assets_dir = None

    def translate_path(self, path):
        if self.assets_dir:
            prefix = "/assets/"
            if path == "/assets" or path.startswith(prefix):
                rel = path[len(prefix):] if path.startswith(prefix) else ""
                rel = rel.split("?", 1)[0].split("#", 1)[0]
                parts = [p for p in rel.split("/") if p and p != ".."]
                return os.path.join(self.assets_dir, *parts)
        return super().translate_path(path)

    # Cross-origin isolation (kept for SharedArrayBuffer-style features and the
    # WebGPU/pthread paths). no-store keeps the dev loop honest: a stale
    # openra3.js/.wasm in the browser cache hides new builds (the worker's
    # importScripts especially).
    def end_headers(self):
        self.send_header("Cross-Origin-Opener-Policy", "same-origin")
        self.send_header("Cross-Origin-Embedder-Policy", "require-corp")
        self.send_header("Cache-Control", "no-store, max-age=0")
        super().end_headers()

    def send_head(self):
        header = self.headers.get("Range")
        if not header:
            return super().send_head()

        path = self.translate_path(self.path)
        if os.path.isdir(path):
            return super().send_head()
        try:
            handle = open(path, "rb")
        except OSError:
            self.send_error(404, "File not found")
            return None

        match = _RANGE.match(header.strip())
        if not match:
            handle.close()
            return super().send_head()

        size = os.fstat(handle.fileno()).st_size
        start = int(match.group(1)) if match.group(1) else 0
        end = int(match.group(2)) if match.group(2) else size - 1
        if start > end or start >= size:
            handle.close()
            self.send_error(416, "Requested Range Not Satisfiable")
            return None
        end = min(end, size - 1)

        self.send_response(206)
        self.send_header("Content-Type", self.guess_type(path))
        self.send_header("Accept-Ranges", "bytes")
        self.send_header("Content-Range", f"bytes {start}-{end}/{size}")
        self.send_header("Content-Length", str(end - start + 1))
        self.send_header("Cache-Control", "no-store")
        self.end_headers()
        handle.seek(start)
        self._remaining = end - start + 1
        return handle

    def copyfile(self, source, outputfile):
        remaining = getattr(self, "_remaining", None)
        if remaining is None:
            return super().copyfile(source, outputfile)
        try:
            while remaining > 0:
                chunk = source.read(min(65536, remaining))
                if not chunk:
                    break
                outputfile.write(chunk)
                remaining -= len(chunk)
        finally:
            self._remaining = None


def main() -> int:
    parser = argparse.ArgumentParser(description="OpenRA3 wasm dev server")
    parser.add_argument("--root", default="build/wasm/bin", help="directory to serve")
    parser.add_argument("--assets", default=None, help="directory served for /assets (the lazy asset tree)")
    parser.add_argument("--port", type=int, default=8199)
    parser.add_argument("--bind", default="127.0.0.1")
    args = parser.parse_args()

    if not os.path.isdir(args.root):
        print(f"root not found: {args.root}", file=sys.stderr)
        return 1
    if args.assets and not os.path.isdir(args.assets):
        print(f"assets not found: {args.assets}", file=sys.stderr)
        return 1
    RangeHandler.assets_dir = os.path.abspath(args.assets) if args.assets else None
    handler = functools.partial(RangeHandler, directory=args.root)
    server = ThreadingHTTPServer((args.bind, args.port), handler)
    print(f"serving {args.root} at http://{args.bind}:{args.port}/index.html")
    if RangeHandler.assets_dir:
        print(f"  /assets -> {RangeHandler.assets_dir}")
    try:
        server.serve_forever()
    except KeyboardInterrupt:
        pass
    return 0


if __name__ == "__main__":
    raise SystemExit(main())