from __future__ import annotations

import re
from pathlib import Path
from typing import Any


PROMPT_ROOT = Path(__file__).resolve().parent.parent / "prompts"
_TOKEN_RE = re.compile(r"{{\s*([A-Za-z_][A-Za-z0-9_]*)\s*}}")


def load_prompt_template(relative_path: str) -> str:
    path = (PROMPT_ROOT / relative_path).resolve()
    if not path.is_relative_to(PROMPT_ROOT.resolve()):
        raise ValueError(f"Invalid prompt path: {relative_path}")
    return path.read_text(encoding="utf-8")


def render_prompt_template(template: str, **context: Any) -> str:
    def _replace(match: re.Match[str]) -> str:
        value = context.get(match.group(1), "")
        return "" if value is None else str(value)

    return _TOKEN_RE.sub(_replace, template)


def render_prompt(relative_path: str, **context: Any) -> str:
    return render_prompt_template(load_prompt_template(relative_path), **context)