Add onFlush callback to Metrics interface

Author: NonSwag

core/src/main/java/dev/faststats/core/Metrics.java

@@ -83,6 +83,18 @@ interface Factory<T, F extends Factory<T, F>> {
         @Contract(mutates = "this")
         F addChart(Chart<?> chart) throws IllegalArgumentException;
 
+        /**
+         * Sets the flush callback for this metrics instance.
+         * <p>
+         * This callback will be invoked when the metrics have been submitted to, and accepted by, the metrics server.
+         *
+         * @param flush the flush callback
+         * @return the metrics factory
+         * @since 0.15.0
+         */
+        @Contract(mutates = "this")
+        F onFlush(Runnable flush);
+
         /**
          * Sets the error tracker for this metrics instance.
          * <p>

core/src/main/java/dev/faststats/core/SimpleMetrics.java

@@ -45,6 +45,7 @@ public abstract class SimpleMetrics implements Metrics {
     private final Config config;
     private final @Token String token;
     private final @Nullable ErrorTracker tracker;
+    private final @Nullable Runnable flush;
     private final URI url;
     private final boolean debug;
 
@@ -58,6 +59,7 @@ protected SimpleMetrics(final Factory<?, ?> factory, final Config config) throws
         this.debug = factory.debug || Boolean.getBoolean("faststats.debug") || config.debug();
         this.token = factory.token;
         this.tracker = config.errorTracking ? factory.tracker : null;
+        this.flush = factory.flush;
         this.url = factory.url;
     }
 
@@ -72,6 +74,7 @@ protected SimpleMetrics(
             final Set<Chart<?>> charts,
             @Token final String token,
             @Nullable final ErrorTracker tracker,
+            @Nullable final Runnable flush,
             final URI url,
             final boolean debug
     ) {
@@ -84,6 +87,7 @@ protected SimpleMetrics(
         this.debug = debug;
         this.token = token;
         this.tracker = tracker;
+        this.flush = flush;
         this.url = url;
     }
 
@@ -201,6 +205,7 @@ private boolean submitNow() throws IOException {
                 if (statusCode >= 200 && statusCode < 300) {
                     info("Metrics submitted with status code: " + statusCode + " (" + body + ")");
                     getErrorTracker().map(SimpleErrorTracker.class::cast).ifPresent(SimpleErrorTracker::clear);
+                    if (flush != null) flush.run();
                     return true;
                 } else if (statusCode >= 300 && statusCode < 400) {
                     warn("Received redirect response from metrics server: " + statusCode + " (" + body + ")");
@@ -320,6 +325,7 @@ public abstract static class Factory<T, F extends Metrics.Factory<T, F>> impleme
         private final Set<Chart<?>> charts = new HashSet<>(0);
         private URI url = URI.create("https://metrics.faststats.dev/v1/collect");
         private @Nullable ErrorTracker tracker;
+        private @Nullable Runnable flush;
         private @Nullable String token;
         private boolean debug = false;
 
@@ -330,6 +336,13 @@ public F addChart(final Chart<?> chart) throws IllegalArgumentException {
             return (F) this;
         }
 
+        @Override
+        @SuppressWarnings("unchecked")
+        public F onFlush(final Runnable flush) {
+            this.flush = flush;
+            return (F) this;
+        }
+
         @Override
         @SuppressWarnings("unchecked")
         public F errorTracker(final ErrorTracker tracker) {

core/src/test/java/dev/faststats/MockMetrics.java

@@ -14,7 +14,7 @@
 @NullMarked
 public class MockMetrics extends SimpleMetrics {
     public MockMetrics(final UUID serverId, @Token final String token, @Nullable final ErrorTracker tracker, final boolean debug) {
-        super(new Config(serverId, true, debug, true, true, false, false), Set.of(), token, tracker, URI.create("http://localhost:5000/v1/collect"), debug);
+        super(new Config(serverId, true, debug, true, true, false, false), Set.of(), token, tracker, null, URI.create("http://localhost:5000/v1/collect"), debug);
     }
 
     @Override