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fluxer_media_proxy/src/lib/InMemoryCoalescer.ts

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+/*
+ * Copyright (C) 2026 Fluxer Contributors
+ *
+ * This file is part of Fluxer.
+ *
+ * Fluxer is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Fluxer 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Fluxer. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import * as metrics from '~/lib/MetricsClient';
+
+export class InMemoryCoalescer {
+	private pending = new Map<string, Promise<unknown>>();
+
+	async coalesce<T>(key: string, fn: () => Promise<T>): Promise<T> {
+		const existing = this.pending.get(key) as Promise<T> | undefined;
+		if (existing) {
+			metrics.counter({name: 'media_proxy.cache.hit'});
+			return existing;
+		}
+
+		metrics.counter({name: 'media_proxy.cache.miss'});
+
+		const promise = (async () => {
+			try {
+				return await fn();
+			} finally {
+				this.pending.delete(key);
+			}
+		})();
+
+		this.pending.set(key, promise);
+		return promise;
+	}
+}