"""LLM provider interface — provider-agnostic by design.

The default provider is ``null`` (no network calls, no LLM). Components must
degrade gracefully when the provider is null: rule-based fallbacks kick in.

Adding a provider = implementing ``LLMProvider.complete`` and registering it in
``get_provider``. Provider and model are selected exclusively via env vars
(``CAYCE_OPS_LLM_PROVIDER``, ``CAYCE_OPS_LLM_MODEL``).
"""

from __future__ import annotations

import json
import urllib.request
from typing import Protocol


class LLMProvider(Protocol):
    name: str

    def complete(self, prompt: str, *, system: str = "", timeout: float = 30.0) -> str:
        """Return the model's completion for the prompt. Raises on failure."""
        ...  # pragma: no cover


class NullProvider:
    """No-op provider: never touches the network. Signals 'no LLM available'."""

    name = "null"

    def complete(self, prompt: str, *, system: str = "", timeout: float = 30.0) -> str:
        raise RuntimeError("LLM provider is 'null': no LLM configured")


class OpenAICompatProvider:
    """Minimal OpenAI-compatible /chat/completions client (stdlib urllib only).

    Works with OpenAI, OpenRouter, local llama.cpp/vLLM servers, etc.
    """

    name = "openai-compat"

    def __init__(self, base_url: str, api_key: str, model: str) -> None:
        self.base_url = base_url.rstrip("/")
        self.api_key = api_key
        self.model = model

    def complete(self, prompt: str, *, system: str = "", timeout: float = 30.0) -> str:
        payload = {
            "model": self.model,
            "messages": (
                ([{"role": "system", "content": system}] if system else [])
                + [{"role": "user", "content": prompt}]
            ),
            "temperature": 0.0,
        }
        req = urllib.request.Request(
            f"{self.base_url}/chat/completions",
            data=json.dumps(payload).encode(),
            headers={
                "Content-Type": "application/json",
                "Authorization": f"Bearer {self.api_key}",
            },
            method="POST",
        )
        with urllib.request.urlopen(req, timeout=timeout) as resp:  # noqa: S310 (base_url is operator-configured)
            body = json.loads(resp.read().decode())
        return body["choices"][0]["message"]["content"]


def get_provider(cfg=None) -> LLMProvider:
    """Build the provider named by CAYCE_OPS_LLM_PROVIDER (default: null)."""
    from cayceops.config import load

    cfg = cfg or load()
    if cfg.llm_provider == "null":
        return NullProvider()
    if cfg.llm_provider == "openai-compat":
        return OpenAICompatProvider(cfg.llm_base_url, cfg.llm_api_key, cfg.llm_model)
    raise ValueError(f"unknown LLM provider: {cfg.llm_provider!r}")