core[minor]: Add FakeVectorStore to core testing utils (#6186)

* core[minor]: Add FakeVectorStore to core testing utils

* chore: lint files

langchain-core/src/utils/testing/index.ts

@@ -2,6 +2,7 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 /* eslint-disable @typescript-eslint/no-unused-vars */
 
+import { similarity as ml_distance_similarity } from "ml-distance";
 import { z } from "zod";
 import {
   BaseCallbackConfig,
@@ -34,12 +35,17 @@ import { BaseRetriever } from "../../retrievers/index.js";
 import { Runnable, RunnableLambda } from "../../runnables/base.js";
 import { StructuredTool, ToolParams } from "../../tools/index.js";
 import { BaseTracer, Run } from "../../tracers/base.js";
-import { Embeddings, EmbeddingsParams } from "../../embeddings.js";
+import {
+  Embeddings,
+  EmbeddingsInterface,
+  EmbeddingsParams,
+} from "../../embeddings.js";
 import {
   StructuredOutputMethodParams,
   BaseLanguageModelInput,
   StructuredOutputMethodOptions,
 } from "../../language_models/base.js";
+import { VectorStore } from "../../vectorstores.js";
 
 /**
  * Parser for comma-separated values. It splits the input text by commas
@@ -709,3 +715,191 @@ export class SingleRunExtractor extends BaseTracer {
     return this.runPromise;
   }
 }
+
+/**
+ * Interface representing a vector in memory. It includes the content
+ * (text), the corresponding embedding (vector), and any associated
+ * metadata.
+ */
+interface MemoryVector {
+  content: string;
+  embedding: number[];
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  metadata: Record<string, any>;
+}
+
+/**
+ * Interface for the arguments that can be passed to the
+ * `FakeVectorStore` constructor. It includes an optional `similarity`
+ * function.
+ */
+export interface FakeVectorStoreArgs {
+  similarity?: typeof ml_distance_similarity.cosine;
+}
+
+/**
+ * Class that extends `VectorStore` to store vectors in memory. Provides
+ * methods for adding documents, performing similarity searches, and
+ * creating instances from texts, documents, or an existing index.
+ */
+export class FakeVectorStore extends VectorStore {
+  declare FilterType: (doc: Document) => boolean;
+
+  memoryVectors: MemoryVector[] = [];
+
+  similarity: typeof ml_distance_similarity.cosine;
+
+  _vectorstoreType(): string {
+    return "memory";
+  }
+
+  constructor(
+    embeddings: EmbeddingsInterface,
+    { similarity, ...rest }: FakeVectorStoreArgs = {}
+  ) {
+    super(embeddings, rest);
+
+    this.similarity = similarity ?? ml_distance_similarity.cosine;
+  }
+
+  /**
+   * Method to add documents to the memory vector store. It extracts the
+   * text from each document, generates embeddings for them, and adds the
+   * resulting vectors to the store.
+   * @param documents Array of `Document` instances to be added to the store.
+   * @returns Promise that resolves when all documents have been added.
+   */
+  async addDocuments(documents: Document[]): Promise<void> {
+    const texts = documents.map(({ pageContent }) => pageContent);
+    return this.addVectors(
+      await this.embeddings.embedDocuments(texts),
+      documents
+    );
+  }
+
+  /**
+   * Method to add vectors to the memory vector store. It creates
+   * `MemoryVector` instances for each vector and document pair and adds
+   * them to the store.
+   * @param vectors Array of vectors to be added to the store.
+   * @param documents Array of `Document` instances corresponding to the vectors.
+   * @returns Promise that resolves when all vectors have been added.
+   */
+  async addVectors(vectors: number[][], documents: Document[]): Promise<void> {
+    const memoryVectors = vectors.map((embedding, idx) => ({
+      content: documents[idx].pageContent,
+      embedding,
+      metadata: documents[idx].metadata,
+    }));
+
+    this.memoryVectors = this.memoryVectors.concat(memoryVectors);
+  }
+
+  /**
+   * Method to perform a similarity search in the memory vector store. It
+   * calculates the similarity between the query vector and each vector in
+   * the store, sorts the results by similarity, and returns the top `k`
+   * results along with their scores.
+   * @param query Query vector to compare against the vectors in the store.
+   * @param k Number of top results to return.
+   * @param filter Optional filter function to apply to the vectors before performing the search.
+   * @returns Promise that resolves with an array of tuples, each containing a `Document` and its similarity score.
+   */
+  async similaritySearchVectorWithScore(
+    query: number[],
+    k: number,
+    filter?: this["FilterType"]
+  ): Promise<[Document, number][]> {
+    const filterFunction = (memoryVector: MemoryVector) => {
+      if (!filter) {
+        return true;
+      }
+
+      const doc = new Document({
+        metadata: memoryVector.metadata,
+        pageContent: memoryVector.content,
+      });
+      return filter(doc);
+    };
+    const filteredMemoryVectors = this.memoryVectors.filter(filterFunction);
+    const searches = filteredMemoryVectors
+      .map((vector, index) => ({
+        similarity: this.similarity(query, vector.embedding),
+        index,
+      }))
+      .sort((a, b) => (a.similarity > b.similarity ? -1 : 0))
+      .slice(0, k);
+
+    const result: [Document, number][] = searches.map((search) => [
+      new Document({
+        metadata: filteredMemoryVectors[search.index].metadata,
+        pageContent: filteredMemoryVectors[search.index].content,
+      }),
+      search.similarity,
+    ]);
+
+    return result;
+  }
+
+  /**
+   * Static method to create a `FakeVectorStore` instance from an array of
+   * texts. It creates a `Document` for each text and metadata pair, and
+   * adds them to the store.
+   * @param texts Array of texts to be added to the store.
+   * @param metadatas Array or single object of metadata corresponding to the texts.
+   * @param embeddings `Embeddings` instance used to generate embeddings for the texts.
+   * @param dbConfig Optional `FakeVectorStoreArgs` to configure the `FakeVectorStore` instance.
+   * @returns Promise that resolves with a new `FakeVectorStore` instance.
+   */
+  static async fromTexts(
+    texts: string[],
+    metadatas: object[] | object,
+    embeddings: EmbeddingsInterface,
+    dbConfig?: FakeVectorStoreArgs
+  ): Promise<FakeVectorStore> {
+    const docs: Document[] = [];
+    for (let i = 0; i < texts.length; i += 1) {
+      const metadata = Array.isArray(metadatas) ? metadatas[i] : metadatas;
+      const newDoc = new Document({
+        pageContent: texts[i],
+        metadata,
+      });
+      docs.push(newDoc);
+    }
+    return FakeVectorStore.fromDocuments(docs, embeddings, dbConfig);
+  }
+
+  /**
+   * Static method to create a `FakeVectorStore` instance from an array of
+   * `Document` instances. It adds the documents to the store.
+   * @param docs Array of `Document` instances to be added to the store.
+   * @param embeddings `Embeddings` instance used to generate embeddings for the documents.
+   * @param dbConfig Optional `FakeVectorStoreArgs` to configure the `FakeVectorStore` instance.
+   * @returns Promise that resolves with a new `FakeVectorStore` instance.
+   */
+  static async fromDocuments(
+    docs: Document[],
+    embeddings: EmbeddingsInterface,
+    dbConfig?: FakeVectorStoreArgs
+  ): Promise<FakeVectorStore> {
+    const instance = new this(embeddings, dbConfig);
+    await instance.addDocuments(docs);
+    return instance;
+  }
+
+  /**
+   * Static method to create a `FakeVectorStore` instance from an existing
+   * index. It creates a new `FakeVectorStore` instance without adding any
+   * documents or vectors.
+   * @param embeddings `Embeddings` instance used to generate embeddings for the documents.
+   * @param dbConfig Optional `FakeVectorStoreArgs` to configure the `FakeVectorStore` instance.
+   * @returns Promise that resolves with a new `FakeVectorStore` instance.
+   */
+  static async fromExistingIndex(
+    embeddings: EmbeddingsInterface,
+    dbConfig?: FakeVectorStoreArgs
+  ): Promise<FakeVectorStore> {
+    const instance = new this(embeddings, dbConfig);
+    return instance;
+  }
+}