from __future__ import annotations

import asyncio
from typing import Any

import httpx

from agent_platform.config import Settings

TRANSIENT_COMPLETE_STATUS_CODES = frozenset({408, 425, 429, 500, 502, 503, 504, 524})
COMPLETE_MAX_ATTEMPTS = 2
MAX_RETRY_DELAY_SECONDS = 5.0


def completions_url(base_url: str) -> str:
    base = base_url.rstrip("/")
    if base.endswith("/v1"):
        return f"{base}/chat/completions"
    return f"{base}/v1/chat/completions"


def retry_delay_seconds(response: httpx.Response | None, attempt: int) -> float:
    if response is not None:
        retry_after = response.headers.get("Retry-After")
        if retry_after:
            try:
                return min(MAX_RETRY_DELAY_SECONDS, max(0.0, float(retry_after)))
            except ValueError:
                pass
    return min(MAX_RETRY_DELAY_SECONDS, float(2 ** (attempt - 1)))


class ModelProvider:
    def __init__(self, settings: Settings, client: httpx.AsyncClient | None = None) -> None:
        self.settings = settings
        self.client = client or httpx.AsyncClient(
            timeout=httpx.Timeout(settings.model_timeout_seconds),
            limits=httpx.Limits(max_connections=50, max_keepalive_connections=20),
        )
        self._owns_client = client is None

    @property
    def headers(self) -> dict[str, str]:
        return {
            "Authorization": f"Bearer {self.settings.model_api_key}",
            "Content-Type": "application/json",
        }

    async def close(self) -> None:
        if self._owns_client:
            await self.client.aclose()

    async def complete(
        self,
        *,
        model: str,
        messages: list[dict[str, Any]],
        tools: list[dict[str, Any]] | None = None,
        temperature: float | None = None,
    ) -> dict[str, Any]:
        payload: dict[str, Any] = {
            "model": model,
            "messages": messages,
            "stream": False,
        }
        if tools:
            payload["tools"] = tools
            payload["tool_choice"] = "auto"
        if temperature is not None:
            payload["temperature"] = temperature
        for attempt in range(1, COMPLETE_MAX_ATTEMPTS + 1):
            try:
                response = await self.client.post(
                    completions_url(self.settings.model_api_base_url),
                    headers=self.headers,
                    json=payload,
                )
            except httpx.TransportError:
                if attempt >= COMPLETE_MAX_ATTEMPTS:
                    raise
                await asyncio.sleep(retry_delay_seconds(None, attempt))
                continue

            if response.status_code in TRANSIENT_COMPLETE_STATUS_CODES and attempt < COMPLETE_MAX_ATTEMPTS:
                await response.aread()
                await asyncio.sleep(retry_delay_seconds(response, attempt))
                continue

            response.raise_for_status()
            data = response.json()
            if not data.get("choices"):
                raise RuntimeError("Model provider returned no choices")
            return data

        raise RuntimeError("Model provider retry loop exited unexpectedly")

    async def forward(self, payload: dict[str, Any]) -> httpx.Response:
        request = self.client.build_request(
            "POST",
            completions_url(self.settings.model_api_base_url),
            headers=self.headers,
            json=payload,
        )
        response = await self.client.send(request, stream=bool(payload.get("stream")))
        if response.status_code >= 400:
            await response.aread()
            response.raise_for_status()
        return response