feat: add semantic fact search and embeddings

src/core/utils.ts

@@ -1,4 +1,4 @@
-import { randomUUID } from 'node:crypto';
+import { createHash, randomUUID } from 'node:crypto';
 
 import type { Fact, FactTopic, Topic } from '../types/api';
 import type { FactRecord, TopicRecord } from '../types/domain';
@@ -35,6 +35,42 @@ export function deserializeMetadata(metadata: string | null): unknown | null {
   return JSON.parse(metadata);
 }
 
+export function serializeEmbedding(embedding: number[]): string {
+  return JSON.stringify(embedding);
+}
+
+export function deserializeEmbedding(embedding: string): number[] {
+  return JSON.parse(embedding) as number[];
+}
+
+export function createContentHash(input: string): string {
+  return createHash('sha256').update(input).digest('hex');
+}
+
+export function cosineSimilarity(left: number[], right: number[]): number {
+  if (left.length === 0 || left.length !== right.length) {
+    return 0;
+  }
+
+  let dot = 0;
+  let leftMagnitude = 0;
+  let rightMagnitude = 0;
+
+  for (let index = 0; index < left.length; index += 1) {
+    const leftValue = left[index] ?? 0;
+    const rightValue = right[index] ?? 0;
+    dot += leftValue * rightValue;
+    leftMagnitude += leftValue * leftValue;
+    rightMagnitude += rightValue * rightValue;
+  }
+
+  if (leftMagnitude === 0 || rightMagnitude === 0) {
+    return 0;
+  }
+
+  return dot / (Math.sqrt(leftMagnitude) * Math.sqrt(rightMagnitude));
+}
+
 export function mapTopicRow(record: TopicRecord): Topic {
   return {
     id: record.id,