"""Anomaly selection and the small "drift" tricks.

Nothing here screams. An anomaly is a single property quietly swapped for a
plausible variant. The drift helpers change wording, punctuation, and the
heading itself so the player can never compare two loops character-for-character
and must fall back on memory of *meaning*.
"""

from __future__ import annotations

import random
from typing import Dict, List, Optional, Tuple


def pick_anomaly(properties: Dict[str, dict], rng: random.Random) -> Tuple[str, str]:
    """Choose one property and one of its anomalous values.

    Returns (property_name, anomaly_value).
    """
    candidates = [name for name, spec in properties.items() if spec.get("anomalies")]
    prop = rng.choice(candidates)
    value = rng.choice(list(properties[prop]["anomalies"].keys()))
    return prop, value


def drift_heading(title_variants: List[str], loops: int, rng: random.Random) -> str:
    """The heading is usually 'Hallway 8', but every so often it slips.

    Early on it is stable. The longer the player survives, the more the
    heading is allowed to wander -- a meta anomaly they can never act on.
    """
    if loops < 4:
        return title_variants[0]
    # a small, growing chance of a slipped heading
    if rng.random() < min(0.05 + loops * 0.01, 0.30):
        return rng.choice(title_variants)
    return title_variants[0]


def drift_sign(sign_variants: List[str], rng: random.Random) -> str:
    """The exit sign's spacing/arrow drifts even when it is *not* the anomaly."""
    return rng.choice(sign_variants)


def render_sentence(template: str, sign_text: str) -> str:
    """Fill the shared placeholders in a sentence template."""
    return template.replace("{SIGN}", sign_text)