"""Load and render TOML-backed LLM prompt templates."""

from __future__ import annotations

import tomllib
from dataclasses import dataclass
from functools import cache
from pathlib import Path


@dataclass(frozen=True)
class Prompt:
    """A system and user prompt pair loaded from TOML."""

    system: str
    user: str

    def messages(self, **values: str) -> list[dict[str, str]]:
        """Render this prompt as OpenAI-style chat messages."""
        return [
            {"role": "system", "content": self.system.format(**values)},
            {"role": "user", "content": self.user.format(**values)},
        ]


@cache
def _get_prompt_dir() -> Path:
    """Return the directory containing prompt template files."""
    return Path(__file__).resolve().parent


@cache
def load_prompt(name: str) -> Prompt:
    """Load and validate a named system and user prompt pair from TOML."""
    path = _get_prompt_dir() / f"{name}.toml"
    with path.open("rb") as file:
        body = tomllib.load(file)

    system = body.get("system")
    user = body.get("user")
    if not isinstance(system, str) or not isinstance(user, str):
        msg = f"{path} must define string system and user prompts"
        raise TypeError(msg)
    return Prompt(system=system, user=user)