feat: new file

backend/app/services/forecast.py

@@ -0,0 +1,28 @@
+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)
+