"""Serve output/web/ on http://localhost:8000/ with HTTP Range support, which PMTiles needs.

Python's built-in `python -m http.server` ignores Range headers and always returns the whole file, so the
pmtiles JavaScript library cannot read a tile directory from it. This adds byte-range responses (206).
Usage:  python serve.py [port]
"""
import os
import re
import sys
from functools import partial
from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
from pathlib import Path

WEB = Path(__file__).resolve().parent / "output" / "web"


class RangeHandler(SimpleHTTPRequestHandler):
    extensions_map = {**SimpleHTTPRequestHandler.extensions_map, ".pmtiles": "application/octet-stream"}

    def send_head(self):
        match = re.fullmatch(r"bytes=(\d*)-(\d*)", self.headers.get("Range", ""))
        path = self.translate_path(self.path)
        if not match or not os.path.isfile(path):
            return super().send_head()
        size = os.path.getsize(path)
        start, end = match.groups()
        if start == "":                                  # "bytes=-500": the last 500 bytes
            start, end = max(size - int(end), 0), size - 1
        else:
            start, end = int(start), min(int(end) if end else size - 1, size - 1)
        if start >= size:
            self.send_error(416, "Requested range not satisfiable")
            return None
        f = open(path, "rb")
        f.seek(start)
        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(end - start + 1))
        self.send_header("Accept-Ranges", "bytes")
        self.end_headers()
        self._remaining = end - start + 1
        return f

    def copyfile(self, source, outputfile):
        remaining = getattr(self, "_remaining", None)
        if remaining is None:
            return super().copyfile(source, outputfile)
        while remaining > 0 and (chunk := source.read(min(65536, remaining))):
            outputfile.write(chunk)
            remaining -= len(chunk)
        self._remaining = None


if __name__ == "__main__":
    port = int(sys.argv[1]) if len(sys.argv) > 1 else 8000
    server = ThreadingHTTPServer(("127.0.0.1", port), partial(RangeHandler, directory=str(WEB)))
    print(f"serving {WEB} on http://localhost:{port}/  (Ctrl+C to stop)")
    server.serve_forever()