import time
from typing import Callable, Optional, TypeVar

import httpx

from infrastructure.epc_client.exceptions import EpcRateLimitError

T = TypeVar("T")


def call_with_retry(
    fn: Callable[[], T],
    max_retries: int = 5,
    backoff_base: float = 1.0,
    backoff_multiplier: float = 2.0,
    max_backoff: float = 60.0,
) -> T:
    """Retry `fn` on transient EPC-API failures: HTTP 429 rate limits and
    transport errors (read/connect timeouts, connection resets). A 429 honours
    the server's `Retry-After`; transport errors back off exponentially. Non-
    transient failures (other 4xx/5xx, mapping errors) propagate immediately."""
    last_exc: Optional[Exception] = None
    for attempt in range(max_retries + 1):
        try:
            return fn()
        except (EpcRateLimitError, httpx.TransportError) as exc:
            last_exc = exc
            if attempt < max_retries:
                if isinstance(exc, EpcRateLimitError) and exc.retry_after is not None:
                    delay = exc.retry_after
                else:
                    delay = backoff_base * (backoff_multiplier**attempt)
                time.sleep(min(delay, max_backoff))
    assert last_exc is not None
    raise last_exc