fix of backend to get 15-min data

csharp/App/Backend/Services/CurrentPriceHistoryService.cs

@@ -214,23 +214,33 @@ public static class CurrentPriceHistoryService
         }
     }
 
-    // data.json is an object keyed by timestamp(s); read Config.CurrentPrice of the last record.
-    private static Double? ExtractCurrentPrice(String json)
+    // data.json is a line-based dump (same format the frontend parseChunkJson consumes):
+    //   Timestamp;<unix>;
+    //   {"Config":{"CurrentPrice":0.19,...},"InverterRecord":{...}}
+    // i.e. a header line then a JSON-record line, possibly repeated. It is NOT a single
+    // JSON object, so parse line by line and return CurrentPrice from the last record.
+    private static Double? ExtractCurrentPrice(String dataJson)
     {
-        using var doc = JsonDocument.Parse(json);
-        if (doc.RootElement.ValueKind != JsonValueKind.Object)
-            return null;
-
-        var found  = false;
-        var record = default(JsonElement);
-        foreach (var prop in doc.RootElement.EnumerateObject())
+        Double? last = null;
+        foreach (var line in dataJson.Split('\n'))
         {
-            record = prop.Value;
-            found  = true;
+            var price = TryReadLinePrice(line.Trim());
+            if (price.HasValue)
+                last = price;
+        }
+        return last;
     }
 
-        if (!found
-            || !record.TryGetProperty("Config", out var config)
+    private static Double? TryReadLinePrice(String line)
+    {
+        if (line.Length == 0 || line[0] != '{')
+            return null; // skip "Timestamp;...;" headers and blank lines
+
+        try
+        {
+            using var doc = JsonDocument.Parse(line);
+            if (doc.RootElement.ValueKind != JsonValueKind.Object
+                || !doc.RootElement.TryGetProperty("Config", out var config)
                 || !config.TryGetProperty("CurrentPrice", out var currentPrice))
                 return null;
 
@@ -242,4 +252,9 @@ public static class CurrentPriceHistoryService
                 _ => null
             };
         }
+        catch
+        {
+            return null; // skip a malformed record line
+        }
+    }
 }