"""Tenant-scoped throttling + standard rate-limit headers (``API-STANDARD.md`` §9)."""

from __future__ import annotations

import time
from typing import Any

from rest_framework.throttling import SimpleRateThrottle

__all__ = ["TenantRateThrottle", "apply_rate_limit_headers"]


class TenantRateThrottle(SimpleRateThrottle):
    """Throttles per tenant *and* per identity, never per IP alone (``TENANCY.md`` §7).

    Requires a ``DEFAULT_THROTTLE_RATES["tenant"]`` rate; when it is absent the
    throttle is a no-op so the kit still runs with zero configuration.
    """

    scope = "tenant"

    def get_rate(self) -> str | None:  # type: ignore[override]
        from django.conf import settings

        rates = getattr(settings, "DEFAULT_THROTTLE_RATES", {})
        return rates.get(self.scope)

    def get_cache_key(self, request: Any, view: Any) -> str | None:
        if not self.rate:
            return None
        from infrasynth.tenancy.context import get_current_tenant

        tenant = get_current_tenant()
        tenant_part = str(tenant.pk) if tenant is not None else "anon"
        ident = self.get_ident(request)
        return f"tenant:{tenant_part}:ratelimit:{self.scope}:{ident}"

    def allow_request(self, request: Any, view: Any) -> bool:
        allowed = super().allow_request(request, view)
        history = getattr(self, "history", [])
        num_requests = getattr(self, "num_requests", 0)
        if num_requests:
            request._rate_limit = {  # type: ignore[attr-defined]
                "limit": num_requests,
                "remaining": max(0, num_requests - len(history)),
                "reset": int(history[-1]) if history else int(time.time()),
            }
        return allowed


def apply_rate_limit_headers(response: Any, request: Any) -> None:
    """Copies throttle state recorded on the request onto the response headers."""
    info = getattr(request, "_rate_limit", None)
    if not info:
        return
    response["X-RateLimit-Limit"] = str(info["limit"])
    response["X-RateLimit-Remaining"] = str(info["remaining"])
    response["X-RateLimit-Reset"] = str(info["reset"])