src/main/frontend/components/apex-chart.ts

@@ -20,6 +20,10 @@ function resolveColor(varName: string): string {
     return resolved;
 }
 
+function sameJson(a: unknown, b: unknown): boolean {
+    return JSON.stringify(a) === JSON.stringify(b);
+}
+
 function isDarkScheme(): boolean {
     return getComputedStyle(document.documentElement).colorScheme.includes('dark');
 }
@@ -113,6 +117,49 @@ export class ApexChart extends LitElement {
         }
     }
 
+    /**
+     * Data-only update: patches the live chart via ApexCharts' own
+     * updateSeries/updateOptions instead of rebuilding it from a full option
+     * set, so the SVG animates from its previous values and zoom/selection
+     * state survives. The patch carries `series` plus, depending on the chart
+     * type, `categories` (axis charts) or `labels` (pie).
+     */
+    async updateData(patchJson: string) {
+        await this.updateComplete;
+        const patch = JSON.parse(patchJson);
+        // Nothing rendered yet — there is no option set to patch onto. The
+        // server only calls this after a full render, so this is a no-op guard.
+        if (!this.lastOptions) return;
+
+        const options = this.lastOptions;
+        // Categories/labels are structural: they only reach the chart through
+        // updateOptions, which redraws. Skip it when they are unchanged, which
+        // is the common case for a pure data refresh.
+        const structural: any = {};
+        if (patch.categories && !sameJson(patch.categories, options.xaxis?.categories)) {
+            structural.xaxis = { ...options.xaxis, categories: patch.categories };
+        }
+        if (patch.labels && !sameJson(patch.labels, options.labels)) {
+            structural.labels = patch.labels;
+        }
+
+        options.series = patch.series;
+        if (patch.categories) options.xaxis = { ...options.xaxis, categories: patch.categories };
+        if (patch.labels) options.labels = patch.labels;
+
+        // Re-resolve the theme-varying keys on the merged options, so a rebuild
+        // after a detach (see connectedCallback) starts from the patched data.
+        const themed = applyThemeOverlay(options);
+        this.lastOptionsJson = JSON.stringify(themed);
+
+        if (!this.chart) return;
+
+        if (Object.keys(structural).length > 0) {
+            await this.chart.updateOptions(structural, false, true);
+        }
+        await this.chart.updateSeries(themed.series, true);
+    }
+
     disconnectedCallback() {
         super.disconnectedCallback();
         window.removeEventListener('dialect-theme-change', this.onThemeChange);

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));
+    }
 }

src/test/java/com/example/components/ApexChartUpdateTest.java

@@ -0,0 +1,102 @@
+package com.example.components;
+
+import com.example.Application;
+import com.example.views.DashboardView;
+import com.vaadin.browserless.SpringBrowserlessTest;
+import com.vaadin.browserless.ViewPackages;
+import com.vaadin.flow.component.UI;
+import com.vaadin.flow.component.internal.PendingJavaScriptInvocation;
+import com.vaadin.flow.component.internal.UIInternals.JavaScriptInvocation;
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Covers the incremental update path of {@link ApexChart} by inspecting the JS
+ * calls queued for the client: a chart that has been rendered gets a data-only
+ * {@code updateData} patch, one that has not gets a full {@code renderChart}.
+ */
+@SpringBootTest(classes = Application.class)
+@ViewPackages(classes = DashboardView.class)
+class ApexChartUpdateTest extends SpringBrowserlessTest {
+
+    private static final List<Double> VALUES = List.of(11.0, 22.0);
+    private static final List<String> CATEGORIES = List.of("Jan", "Feb");
+
+    @Test
+    void updateData_afterRender_sendsDataPatch() {
+        navigate(DashboardView.class);
+        LineChart chart = $view(LineChart.class).first();
+        drainInvocations();
+
+        chart.updateData("Umsatz", VALUES, CATEGORIES);
+
+        JavaScriptInvocation call = lastInvocation();
+        assertTrue(call.getExpression().contains("updateData"), call.getExpression());
+        String json = json(call);
+        assertTrue(json.contains("\"series\""), json);
+        assertTrue(json.contains("\"categories\""), json);
+        assertFalse(json.contains("\"colors\""), "a patch carries data only, no theme options: " + json);
+    }
+
+    @Test
+    void updateData_beforeFirstRender_fallsBackToFullRender() {
+        navigate(DashboardView.class);
+        LineChart chart = new LineChart();
+        getCurrentView().getElement().appendChild(chart.getElement());
+        drainInvocations();
+
+        chart.updateData("Umsatz", VALUES, CATEGORIES);
+
+        JavaScriptInvocation call = lastInvocation();
+        assertTrue(call.getExpression().contains("renderChart"), call.getExpression());
+        assertTrue(json(call).contains("\"colors\""), "a full render carries the theme options");
+    }
+
+    @Test
+    void pieChart_updateData_sendsSeriesAndLabels() {
+        navigate(DashboardView.class);
+        PieChart chart = $view(PieChart.class).first();
+        drainInvocations();
+
+        chart.updateData(VALUES, List.of("Nord", "Sued"));
+
+        JavaScriptInvocation call = lastInvocation();
+        assertTrue(call.getExpression().contains("updateData"), call.getExpression());
+        String json = json(call);
+        assertTrue(json.contains("\"series\""), json);
+        assertTrue(json.contains("\"labels\""), json);
+    }
+
+    /** The JSON payload of a {@code callJsFunction} invocation — parameter 0 is
+     *  the element the function is called on. */
+    private String json(JavaScriptInvocation call) {
+        return (String) call.getParameters().get(1);
+    }
+
+    /** Clears everything the view queued while rendering, so the assertions
+     *  only see what the call under test produced. */
+    private void drainInvocations() {
+        dump();
+    }
+
+    private JavaScriptInvocation lastInvocation() {
+        List<PendingJavaScriptInvocation> pending = dump();
+        assertEquals(1, pending.size(), "expected exactly one queued client call");
+        return pending.getFirst().getInvocation();
+    }
+
+    /** {@code callJsFunction} only materialises its invocation in the
+     *  before-client-response phase, which no real client response triggers
+     *  here — so run that phase explicitly before collecting. */
+    private List<PendingJavaScriptInvocation> dump() {
+        UI ui = UI.getCurrent();
+        ui.getInternals().getStateTree().runExecutionsBeforeClientResponse();
+        return ui.getInternals().dumpPendingJavaScriptInvocations();
+    }
+}

src/test/java/com/example/e2e/DashboardChartPlaywrightTest.java

@@ -0,0 +1,58 @@
+package com.example.e2e;
+
+import com.microsoft.playwright.Locator;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static com.microsoft.playwright.assertions.PlaywrightAssertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * End-to-end coverage for the incremental update path of {@code apex-chart.ts}:
+ * a data update must patch the running ApexCharts instance instead of tearing
+ * the chart down and building it again.
+ */
+class DashboardChartPlaywrightTest extends PlaywrightTestBase {
+
+    private static final String PATCH = """
+            {"series":[{"name":"Revenue","data":[1,2,3,4,5,6]}],
+             "categories":["Jan","Feb","Mar","Apr","May","Jun"]}""";
+
+    @BeforeEach
+    void openDashboard() {
+        navigate("");
+    }
+
+    @Test
+    void dataUpdate_keepsTheRenderedSvgInPlace() {
+        Locator chart = page.locator("apex-chart").first();
+        assertThat(chart.locator("svg").first()).isVisible();
+
+        // Tag the live SVG node: a full rebuild would replace it and drop the tag.
+        chart.evaluate("el => el.querySelector('svg').dataset.marker = 'first-render'");
+
+        chart.evaluate("(el, patch) => el.updateData(patch)", PATCH);
+
+        assertEquals(1, chart.locator("svg[data-marker='first-render']").count(),
+                "the chart must be patched in place, not recreated");
+        assertEquals("1,2,3,4,5,6",
+                chart.evaluate("el => JSON.parse(el.lastOptionsJson).series[0].data.join(',')"),
+                "the patched data must have reached the chart");
+    }
+
+    @Test
+    void dataUpdate_keepsTheThemeOverlay() {
+        Locator chart = page.locator("apex-chart").first();
+        assertThat(chart.locator("svg").first()).isVisible();
+
+        chart.evaluate("(el, patch) => el.updateData(patch)", PATCH);
+
+        // grid.borderColor is only ever set by applyThemeOverlay(), from the
+        // resolved --dialect-border token — so a resolved rgb() value here means
+        // the overlay survived the incremental update.
+        Object borderColor = chart.evaluate("el => JSON.parse(el.lastOptionsJson).grid.borderColor");
+        assertTrue(String.valueOf(borderColor).startsWith("rgb"),
+                "expected a resolved theme color, got: " + borderColor);
+    }
+}