src/lib/server/sentenceSimilarity.ts

import { dot } from "@huggingface/transformers";
import type { EmbeddingBackendModel } from "$lib/server/embeddingModels";
import type { Embedding } from "$lib/server/embeddingEndpoints/embeddingEndpoints";

// see here: https://github.com/nmslib/hnswlib/blob/359b2ba87358224963986f709e593d799064ace6/README.md?plain=1#L34
export function innerProduct(embeddingA: Embedding, embeddingB: Embedding) {
	return 1.0 - dot(embeddingA, embeddingB);
}

export async function getSentenceSimilarity(
	embeddingModel: EmbeddingBackendModel,
	query: string,
	sentences: string[]
): Promise<{ distance: number; embedding: Embedding; idx: number }[]> {
	const inputs = [
		`${embeddingModel.preQuery}${query}`,
		...sentences.map((sentence) => `${embeddingModel.prePassage}${sentence}`),
	];

	const embeddingEndpoint = await embeddingModel.getEndpoint();
	const output = await embeddingEndpoint({ inputs }).catch((err) => {
		throw Error("Failed to generate embeddings for sentence similarity", { cause: err });
	});

	const queryEmbedding: Embedding = output[0];
	const sentencesEmbeddings: Embedding[] = output.slice(1);

	return sentencesEmbeddings.map((sentenceEmbedding, idx) => ({
		distance: innerProduct(queryEmbedding, sentenceEmbedding),
		embedding: sentenceEmbedding,
		idx,
	}));
}