"""Basic policy guard for Bridge prompts."""
from __future__ import annotations

MAX_PROMPT_LENGTH = 4000
_BLOCKED_PHRASES = frozenset({
    "<placeholder>",
    "TODO",
    "FIXME",
    "your prompt here",
})


def check(prompt: str) -> tuple[bool, str]:
    """Check a prompt against policy rules.

    Returns:
        (True, "") if prompt passes
        (False, reason) if prompt is blocked
    """
    if not prompt or not prompt.strip():
        return False, "prompt is empty"

    if len(prompt) > MAX_PROMPT_LENGTH:
        return False, f"prompt exceeds {MAX_PROMPT_LENGTH} chars (got {len(prompt)})"

    lower = prompt.lower()
    for phrase in _BLOCKED_PHRASES:
        if phrase.lower() in lower:
            return False, f"prompt contains blocked phrase: '{phrase}'"

    return True, ""