"""Build an LLMProvider from environment variables."""

from __future__ import annotations

import os

from physcom.llm.base import LLMProvider


def build_llm_provider(
    provider: str | None = None,
    model: str | None = None,
    host: str | None = None,
) -> LLMProvider | None:
    """Return an LLMProvider, or None if not configured.

    Explicit args (e.g. from a per-request web form) override env vars;
    passing nothing falls back to the env-var-only behavior below.

    LLM_PROVIDER   — provider name ('gemini', 'ollama'; more can be added)
    GEMINI_API_KEY — required when provider is 'gemini' (server env only,
                     never accepted as a request param)
    GEMINI_MODEL   — optional Gemini model name (default: gemini-2.0-flash)
    OLLAMA_MODEL   — optional Ollama model name (default: qwen2.5:7b)
    OLLAMA_HOST    — optional Ollama server URL (default: http://localhost:11434)
    """
    provider = (provider or os.environ.get("LLM_PROVIDER", "")).lower().strip()

    if not provider or provider == "stub":
        return None

    if provider == "gemini":
        api_key = os.environ.get("GEMINI_API_KEY", "")
        if not api_key:
            raise ValueError("Gemini requires GEMINI_API_KEY to be set in the server environment")
        model = model or os.environ.get("GEMINI_MODEL", "gemini-2.0-flash")
        from physcom.llm.providers.gemini import GeminiLLMProvider
        return GeminiLLMProvider(api_key=api_key, model=model)

    if provider == "ollama":
        model = model or os.environ.get("OLLAMA_MODEL", "qwen2.5:7b")
        host = host or os.environ.get("OLLAMA_HOST", "http://localhost:11434")
        from physcom.llm.providers.ollama import OllamaLLMProvider
        return OllamaLLMProvider(model=model, host=host)

    raise ValueError(f"Unknown LLM provider: {provider!r}. Supported: gemini, ollama, stub")