#!/usr/bin/env python3
"""Serve production SPA and proxy only /prod-api to the task-owned loopback backend."""
import argparse
from functools import partial
from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
from pathlib import Path
import urllib.error
import urllib.request

DIST = Path(__file__).resolve().parents[2] / 'build_ui/dist'


class Handler(SimpleHTTPRequestHandler):
    backend_port = 18096

    def proxy(self):
        path = self.path[len('/prod-api'):]
        if not path.startswith('/') or path.startswith('//'):
            self.send_error(400)
            return
        headers = {k: v for k, v in self.headers.items()
                   if k.lower() not in ['host', 'connection', 'content-length', 'transfer-encoding']}
        length = int(self.headers.get('Content-Length', '0'))
        if length < 0 or length > 10 * 1024 * 1024:
            self.send_error(413)
            return
        request = urllib.request.Request('http://127.0.0.1:' + str(self.backend_port) + path,
                    data=self.rfile.read(length) if length else None, headers=headers, method=self.command)
        class NoRedirect(urllib.request.HTTPRedirectHandler):
            def redirect_request(self, *args, **kwargs):
                return None
        # Ignore all system/environment HTTP proxies, never follow a backend redirect.
        opener = urllib.request.build_opener(urllib.request.ProxyHandler({}), NoRedirect())
        try:
            response = opener.open(request, timeout=30)
        except urllib.error.HTTPError as error:
            response = error
        except (urllib.error.URLError, TimeoutError):
            self.send_error(502, 'QA backend unavailable; no substituted API response')
            return
        with response:
            data = response.read()
            self.send_response(response.code)
            for key, value in response.headers.items():
                if key.lower() not in ['connection', 'transfer-encoding', 'content-length']:
                    self.send_header(key, value)
            self.send_header('Content-Length', str(len(data)))
            self.end_headers()
            self.wfile.write(data)

    def do_GET(self):
        if self.path.startswith('/prod-api/'):
            return self.proxy()
        requested = self.path.split('?', 1)[0]
        if requested != '/' and not (DIST / requested.lstrip('/')).is_file() and '.' not in requested.rsplit('/', 1)[-1]:
            self.path = '/index.html'
        return super().do_GET()

    def do_POST(self):
        return self.proxy() if self.path.startswith('/prod-api/') else self.send_error(405)

    do_PUT = do_POST
    do_DELETE = do_POST

    def log_message(self, *args):
        # No query strings, headers, payloads, tokens or personal identifiers in access logs.
        pass


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument('--port', type=int, default=18088)
    parser.add_argument('--backend-port', type=int, default=18096)
    args = parser.parse_args()
    if not (DIST / 'index.html').is_file():
        raise SystemExit('Build frontend before serving')
    Handler.backend_port = args.backend_port
    ThreadingHTTPServer(('127.0.0.1', args.port), partial(Handler, directory=str(DIST))).serve_forever()