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frontend/sync-client/src/utils/fix-sized-cache.ts

@@ -0,0 +1,57 @@
+// Implements an in-memory fixed-size cache for document contents,
+
+import type { VaultUpdateId } from "../persistence/database";
+
+// evicting the least recently used documents when the size limit is exceeded.
+export class FixedSizeDocumentCache {
+	private readonly maxSizeInBytes: number;
+	private currentSizeInBytes: number;
+	private readonly cache: Map<VaultUpdateId, Uint8Array>;
+	private usageOrder: VaultUpdateId[];
+
+	public constructor(maxSizeInBytes: number) {
+		this.maxSizeInBytes = maxSizeInBytes;
+		this.currentSizeInBytes = 0;
+		this.cache = new Map();
+		this.usageOrder = [];
+	}
+
+	public get(updateId: VaultUpdateId): Uint8Array | undefined {
+		const entry = this.cache.get(updateId);
+		if (entry) {
+			this.usageOrder = this.usageOrder.filter((id) => id !== updateId);
+			this.usageOrder.push(updateId);
+			return entry;
+		}
+		return undefined;
+	}
+
+	public put(updateId: VaultUpdateId, content: Uint8Array): void {
+		if (content.byteLength > this.maxSizeInBytes) {
+			// Document is too large to fit in the cache
+			return;
+		}
+
+		// If the document is already in the cache, update it
+		const existingEntry = this.cache.get(updateId);
+		if (existingEntry != null) {
+			this.currentSizeInBytes -= existingEntry.byteLength;
+			this.cache.delete(updateId);
+			this.usageOrder = this.usageOrder.filter((id) => id !== updateId);
+		}
+		this.cache.set(updateId, content);
+		this.usageOrder.push(updateId);
+		this.currentSizeInBytes += content.byteLength;
+
+		// Evict least recently used documents if over size limit
+		while (
+			this.currentSizeInBytes > this.maxSizeInBytes &&
+			this.usageOrder.length > 0
+		) {
+			const lruUpdateId = this.usageOrder.shift()!; // eslint-disable-line @typescript-eslint/no-non-null-assertion
+			const lruEntry = this.cache.get(lruUpdateId)!; // eslint-disable-line @typescript-eslint/no-non-null-assertion
+			this.cache.delete(lruUpdateId);
+			this.currentSizeInBytes -= lruEntry.byteLength;
+		}
+	}
+}