from __future__ import annotations

from datetime import datetime

from croniter import croniter


SCHEDULE_ALIASES: dict[str, str] = {
    "minute": "* * * * *",
    "minutely": "* * * * *",
    "hour": "0 * * * *",
    "hourly": "0 * * * *",
    "day": "0 0 * * *",
    "daily": "0 0 * * *",
    "week": "0 0 * * 0",
    "weekly": "0 0 * * 0",
    "month": "0 0 1 * *",
    "monthly": "0 0 1 * *",
    "year": "0 0 1 1 *",
    "yearly": "0 0 1 1 *",
}


def normalize_schedule(schedule: str) -> str:
    normalized = (schedule or "").strip()
    if not normalized:
        raise ValueError("Schedule cannot be empty.")

    return SCHEDULE_ALIASES.get(normalized.lower(), normalized)


def validate_schedule(schedule: str) -> str:
    normalized = normalize_schedule(schedule)
    if not croniter.is_valid(normalized):
        raise ValueError(
            "Invalid schedule. Use an alias like daily/weekly/monthly or a cron expression such as '0 */6 * * *'."
        )
    return normalized


def next_run_for_schedule(schedule: str, after: datetime) -> datetime:
    normalized = validate_schedule(schedule)
    return croniter(normalized, after).get_next(datetime)