1 files changed, 59 insertions, 0 deletions
diff --git a/src/main/java/io/github/moulberry/notenoughupdates/util/AsyncDependencyLoaderImpl.java b/src/main/java/io/github/moulberry/notenoughupdates/util/AsyncDependencyLoaderImpl.java
new file mode 100644
index 00000000..4b7f2fb8
--- /dev/null
+++ b/src/main/java/io/github/moulberry/notenoughupdates/util/AsyncDependencyLoaderImpl.java
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2022 NotEnoughUpdates contributors
+ *
+ * This file is part of NotEnoughUpdates.
+ *
+ * NotEnoughUpdates is free software: you can redistribute it
+ * and/or modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation, either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * NotEnoughUpdates is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with NotEnoughUpdates. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package io.github.moulberry.notenoughupdates.util;
+
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+class AsyncDependencyLoaderImpl<R, T> implements AsyncDependencyLoader<T> {
+
+	private final Supplier<R> supplyDependency;
+	private final Function<R, CompletableFuture<T>> generator;
+	private final BiFunction<R, R, Boolean> isDifferent;
+	private volatile CompletableFuture<T> lastValue;
+	private volatile R lastDependency;
+	private volatile boolean isFirstFire = true;
+
+	@Override
+	public synchronized Optional<T> peekValue() {
+		R nextDependency = supplyDependency.get();
+		if (isFirstFire || isDifferent.apply(nextDependency, lastDependency)) {
+			isFirstFire = false;
+			if (lastValue != null)
+				lastValue.cancel(true);
+			lastValue = generator.apply(nextDependency);
+		}
+		lastDependency = nextDependency;
+		return Optional.ofNullable(lastValue.getNow(null));
+	}
+
+	AsyncDependencyLoaderImpl(
+		Supplier<R> supplyDependency,
+		Function<R, CompletableFuture<T>> generator,
+		BiFunction<R, R, Boolean> isDifferent
+	) {
+		this.supplyDependency = supplyDependency;
+		this.generator = generator;
+		this.isDifferent = isDifferent;
+	}
+}