Don't create models in backups/import

ts/services/backups/util/CircularMessageCache.ts

@@ -0,0 +1,80 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type {
+  ReadonlyMessageAttributesType,
+  MessageAttributesType,
+} from '../../../model-types.d';
+import { find } from '../../../util/iterables';
+import { DataReader } from '../../../sql/Client';
+
+export type CircularMessageCacheOptionsType = Readonly<{
+  size: number;
+  flush: () => Promise<void>;
+}>;
+
+export class CircularMessageCache {
+  private readonly flush: () => Promise<void>;
+  private readonly buffer: Array<MessageAttributesType | undefined>;
+  private readonly sentAtToMessages = new Map<
+    number,
+    Set<MessageAttributesType>
+  >();
+  private offset = 0;
+
+  constructor({ size, flush }: CircularMessageCacheOptionsType) {
+    this.flush = flush;
+    this.buffer = new Array(size);
+  }
+
+  public push(attributes: MessageAttributesType): void {
+    const stale = this.buffer[this.offset];
+    this.buffer[this.offset] = attributes;
+    this.offset = (this.offset + 1) % this.buffer.length;
+
+    let addedSet = this.sentAtToMessages.get(attributes.sent_at);
+    if (addedSet === undefined) {
+      addedSet = new Set();
+      this.sentAtToMessages.set(attributes.sent_at, addedSet);
+    }
+    addedSet.add(attributes);
+
+    if (stale === undefined) {
+      return;
+    }
+
+    const staleSet = this.sentAtToMessages.get(stale.sent_at);
+    if (staleSet === undefined) {
+      return;
+    }
+    staleSet.delete(stale);
+    if (staleSet.size === 0) {
+      this.sentAtToMessages.delete(stale.sent_at);
+    }
+  }
+
+  public async findBySentAt(
+    sentAt: number,
+    predicate: (attributes: ReadonlyMessageAttributesType) => boolean
+  ): Promise<MessageAttributesType | undefined> {
+    const set = this.sentAtToMessages.get(sentAt);
+    if (set !== undefined) {
+      const cached = find(set.values(), predicate);
+      if (cached != null) {
+        return cached;
+      }
+    }
+
+    await this.flush();
+
+    const onDisk = await DataReader.getMessagesBySentAt(sentAt);
+    return onDisk.find(predicate);
+  }
+
+  // Just a stub to conform with the interface
+  public async upgradeSchema(
+    attributes: MessageAttributesType
+  ): Promise<MessageAttributesType> {
+    return attributes;
+  }
+}