from __future__ import annotations

import numpy as np
from statsmodels.tsa.holtwinters import ExponentialSmoothing


def forecast_next_n(y: np.ndarray, n: int) -> np.ndarray:
    """
    轻量级预测：优先 Holt-Winters（对短序列也相对稳），失败则用简单移动平均。
    """
    y = np.asarray(y, dtype=float)
    if y.size < 3:
        return np.repeat(y[-1] if y.size else 0.0, n)

    try:
        model = ExponentialSmoothing(
            y,
            trend="add",
            seasonal=None,
            initialization_method="estimated",
        )
        fit = model.fit(optimized=True)
        return np.asarray(fit.forecast(n), dtype=float)
    except Exception:
        window = int(min(7, max(3, y.size // 2)))
        avg = float(np.mean(y[-window:])) if y.size else 0.0
        return np.repeat(avg, n)