server.py

#!/usr/bin/env python3
"""Single-port static server for the fish schooling simulation.

Usage: python3 server.py [port]   (default 8000)

Serves three things from one port:
    /        landing page linking to the two versions
    /2d/     top-down 2D simulation (Canvas)
    /3d/     3D aquarium simulation (Three.js, vendored locally)

The simulation itself is 100% client-side; this only serves static files.
Any static file server works equally well.
"""
import http.server
import os
import sys

PORT = int(sys.argv[1]) if len(sys.argv) > 1 else 8000
os.chdir(os.path.dirname(os.path.abspath(__file__)))


class Handler(http.server.SimpleHTTPRequestHandler):
    # Correct MIME type for the vendored ES module, regardless of OS defaults.
    extensions_map = {**http.server.SimpleHTTPRequestHandler.extensions_map,
                      ".js": "text/javascript", ".mjs": "text/javascript"}

    def send_head(self):
        # Redirect the bare paths to their directory so relative imports
        # (e.g. ./vendor/three...) resolve against /2d/ and /3d/.
        if self.path in ("/2d", "/3d"):
            self.send_response(301)
            self.send_header("Location", self.path + "/")
            self.end_headers()
            return None
        return super().send_head()


server = http.server.ThreadingHTTPServer(("", PORT), Handler)
print(f"Fish tank running at http://localhost:{PORT}")
print(f"  landing  http://localhost:{PORT}/")
print(f"  2D       http://localhost:{PORT}/2d/")
print(f"  3D       http://localhost:{PORT}/3d/")
server.serve_forever()