fix: update ApexCharts data in place instead of re-rendering (#23)

Every data change went through renderChart, which rebuilt the chart from a
full option set: animations restarted and zoom/selection state was lost.

Add an updateData path that patches the live chart via ApexCharts'
updateSeries (and updateOptions only when categories/labels actually
change), exposed as AxisChart.updateData / PieChart.updateData. Before the
first render there is nothing to patch, so those fall back to setData.
The theme overlay is re-applied to the merged options, so a rebuild after
a detach starts from the patched data.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0124BiJikbhbiEsNfJxdWM69

src/main/java/com/example/components/ApexChart.java

@@ -17,6 +17,7 @@ public abstract class ApexChart extends Component implements HasSize {
     protected static final JsonMapper MAPPER = JsonMapper.builder().build();
 
     private final String chartType;
+    private boolean optionsSent;
 
     protected ApexChart(String chartType) {
         this.chartType = chartType;
@@ -28,6 +29,23 @@ public abstract class ApexChart extends Component implements HasSize {
 
     protected void sendOptions(Map<String, Object> options) {
         getElement().callJsFunction("renderChart", MAPPER.writeValueAsString(options));
+        optionsSent = true;
+    }
+
+    /**
+     * Sends a data-only patch ({@code series} plus {@code categories} or
+     * {@code labels}) that the client applies to the running chart, instead of
+     * rebuilding it from a full option set. Only valid once
+     * {@link #sendOptions} has run — see {@link #hasSentOptions()}.
+     */
+    protected void sendDataPatch(Map<String, Object> patch) {
+        getElement().callJsFunction("updateData", MAPPER.writeValueAsString(patch));
+    }
+
+    /** Whether a full option set has been sent, i.e. whether there is a chart
+     *  on the client a data patch could be applied to. */
+    protected boolean hasSentOptions() {
+        return optionsSent;
     }
 
     @ClientCallable

src/main/java/com/example/components/AxisChart.java

@@ -20,4 +20,22 @@ public abstract class AxisChart extends ApexChart {
 
         sendOptions(options);
     }
+
+    /**
+     * Replaces the data of an already rendered chart without re-rendering it:
+     * the client patches series (and categories) into the live chart, so the
+     * update animates from the previous values instead of flashing. Falls back
+     * to {@link #setData} as long as nothing has been rendered yet.
+     */
+    public void updateData(String seriesName, List<Double> values, List<String> categories) {
+        if (!hasSentOptions()) {
+            setData(seriesName, values, categories);
+            return;
+        }
+
+        sendDataPatch(Map.of(
+                "series", List.of(Map.of("name", seriesName, "data", values)),
+                "categories", categories
+        ));
+    }
 }

src/main/java/com/example/components/PieChart.java

@@ -16,4 +16,18 @@ public class PieChart extends ApexChart {
 
         sendOptions(options);
     }
+
+    /**
+     * Replaces the data of an already rendered chart without re-rendering it —
+     * see {@link AxisChart#updateData}. Falls back to {@link #setData} as long
+     * as nothing has been rendered yet.
+     */
+    public void updateData(List<Double> values, List<String> labels) {
+        if (!hasSentOptions()) {
+            setData(values, labels);
+            return;
+        }
+
+        sendDataPatch(Map.of("series", values, "labels", labels));
+    }
 }