"""Bounded JSON requests; redirects cannot forward upload credentials."""

import json
from http.client import HTTPException
from urllib.error import HTTPError, URLError
from urllib.request import HTTPRedirectHandler, ProxyHandler, Request, build_opener

from . import __version__


class TransportError(Exception):
    pass


class NoRedirects(HTTPRedirectHandler):
    def redirect_request(self, request, response, code, message, headers, new_url):
        return None


def _invalid_constant(value):
    raise ValueError("Non-finite JSON number")


class JsonHttp:
    MAX_RESPONSE_BYTES = 2 * 1024 * 1024

    def __init__(self, timeout: float, *, local: bool = False):
        handlers = [NoRedirects()]
        if local:
            # LAN traffic must not go through a workstation's HTTP(S) proxy.
            handlers.append(ProxyHandler({}))
        self.opener = build_opener(*handlers)
        self.timeout = timeout

    def request(self, url: str, *, payload: dict | None = None, token: str | None = None, extra_headers=None) -> dict:
        headers = {"Accept": "application/json", "User-Agent": f"solar-relay/{__version__}"}
        headers.update(extra_headers or {})
        body = None
        if payload is not None:
            body = json.dumps(payload, allow_nan=False, separators=(",", ":")).encode("utf-8")
            headers["Content-Type"] = "application/json"
        if token:
            headers["Authorization"] = f"Bearer {token}"
        request = Request(url, data=body, headers=headers, method="POST" if body is not None else "GET")
        try:
            with self.opener.open(request, timeout=self.timeout) as response:
                raw = response.read(self.MAX_RESPONSE_BYTES + 1)
        except HTTPError as error:
            # Do not log server bodies: they can echo request headers or credentials.
            error.close()
            raise TransportError(f"HTTP {error.code}") from None
        except (URLError, OSError, TimeoutError, HTTPException) as error:
            raise TransportError(f"Network request failed ({type(error).__name__})") from None
        if len(raw) > self.MAX_RESPONSE_BYTES:
            raise TransportError("JSON response exceeds 2 MiB")
        try:
            value = json.loads(raw, parse_constant=_invalid_constant)
        except (ValueError, UnicodeError, RecursionError):
            raise TransportError("Response is not valid JSON") from None
        if not isinstance(value, dict):
            raise TransportError("Expected a JSON object")
        return value