"""Input validation, shared by the UI and the public API."""

from __future__ import annotations

import models
from steering.scenarios import BY_ID, ScenarioSpec

#: Generous enough for a sentence, small enough that one run stays inside a single GPU allocation.
MAX_PROMPT_CHARS = 300
MAX_PREFIX_CHARS = 100


def collapse(text: str | None) -> str:
    """Whitespace collapsed to single spaces, the way the model will see the text."""
    return " ".join(str(text or "").split()).strip()


def clean(model: str | None, scenario: str | None, prompt: str | None, prefix: str | None
          ) -> tuple[models.ModelSpec, ScenarioSpec, str, str]:
    """Validated (model, scenario, prompt, opening words). Empty text falls back to the scenario's."""
    spec = BY_ID.get((scenario or "").strip())
    if spec is None:
        raise ValueError(f"Unknown scenario {scenario!r}. Known: {', '.join(sorted(BY_ID))}.")
    prompt = collapse(prompt) or spec.prompt
    prefix = collapse(prefix) or spec.prefix
    if len(prompt) > MAX_PROMPT_CHARS:
        raise ValueError(f"The prompt is longer than {MAX_PROMPT_CHARS} characters.")
    if len(prefix) > MAX_PREFIX_CHARS:
        raise ValueError(f"The opening words are longer than {MAX_PREFIX_CHARS} characters.")
    return models.resolve(model), spec, prompt, prefix