增加 图片识别 缓存，缓存日期有等级

Plugins/CloudProduct/Entities/ImageAnalysisCache.cs

@@ -1,4 +1,5 @@
 using FreeSql.DataAnnotations;
+using System.Text.Json;
 
 namespace Store.Modules.CloudProduct.Entities;
 
@@ -14,4 +15,31 @@ public sealed class ImageAnalysisCache
     public string RecognitionResult { get; set; } = "";
     /// <summary>缓存最近更新时间，UTC。</summary>
     public DateTime UpdatedAt { get; set; }
+
+    /// <summary>从 UpdatedAt 起算的缓存有效小时数，命中时不续期。</summary>
+    public int ExpiresAt { get; set; }
+
+    /// <summary>每轮成功识别后更新有效期：空结果逐级延长，有内容则重置级别。</summary>
+    public void RecordExpiration(bool isEmpty, DateTime utcNow)
+    {
+        // 新记录和上次有内容的记录，首次为空时均从 24 小时起算。
+        ExpiresAt = isEmpty ? ExpiresAt switch
+        {
+            24 => 48,
+            48 => 96,
+            96 => 192,
+            192 or 384 => 384,
+            _ => 24
+        } : 720;
+        UpdatedAt = utcNow;
+    }
+
+    /// <summary>仅复用有效期内的数组，旧对象格式需要重新识别。</summary>
+    public string[]? ReadFreshResult(DateTime utcNow)
+    {
+        if (utcNow >= UpdatedAt.AddHours(ExpiresAt) || !RecognitionResult.TrimStart().StartsWith('['))
+            return null;
+
+        return JsonSerializer.Deserialize<string[]>(RecognitionResult);
+    }
 }