feat(viewer): add similarity search

- Introduces a new submodule `utils/search` that provides the search
  features. So far, it provides a function `searchSimilarMumblings` that
  performs similarity search on mumblings.

issue codemonger-io#28

cdk/viewer/src/utils/search.ts

@@ -0,0 +1,50 @@
+import * as util from 'node:util';
+import { InvokeCommand, LambdaClient } from '@aws-sdk/client-lambda';
+
+// Shared Lambda client.
+let lambda: LambdaClient | null = null;
+
+/** Mumbling in similarity search results. */
+export interface SimilarMumbling {
+  /** ID (URL) of the mumbling fragment. */
+  id: string;
+  /** Approximate squared distance. */
+  distance: number;
+}
+
+/**
+ * Searches embeddings similar to a given query.
+ *
+ * @remarks
+ *
+ * You have to specify the name of the Lambda function that performs actual
+ * search to the environment variable `SEARCH_SIMILAR_MUMBLINGS_FUNCTION_NAME`.
+ */
+export async function searchSimilarMumblings(
+  embedding: [number],
+): Promise<[SimilarMumbling]> {
+  if (process.env.SEARCH_SIMILAR_MUMBLINGS_FUNCTION_NAME == null) {
+    throw new Error('SEARCH_SIMILAR_MUMBLINGS_FUNCTION_NAME is not set');
+  }
+  if (lambda == null) {
+    lambda = new LambdaClient({});
+  }
+  const res = await lambda.send(new InvokeCommand({
+    FunctionName: process.env.SEARCH_SIMILAR_MUMBLINGS_FUNCTION_NAME,
+    InvocationType: 'RequestResponse',
+    Payload: JSON.stringify(embedding),
+  }));
+  if (res.StatusCode !== 200){
+    throw new Error(`similarity search function failed with ${res.StatusCode}`);
+  }
+  if (res.Payload == null) {
+    throw new Error('similarity search function returned nothing');
+  }
+  const data = new util.TextDecoder().decode(res.Payload);
+  const results = JSON.parse(data);
+  if (!Array.isArray(results)) {
+    throw new Error('similarity search function returned non-array');
+  }
+  // TODO: verify results
+  return results as [SimilarMumbling];
+}