src/lib/buildPrompt.ts

import type { BackendModel } from "./server/models";
import type { Message } from "./types/Message";
import { format } from "date-fns";
import type { WebSearch } from "./types/WebSearch";
import { downloadFile } from "./server/files/downloadFile";
import type { Conversation } from "./types/Conversation";

interface buildPromptOptions {
	messages: Pick<Message, "from" | "content" | "files">[];
	id?: Conversation["_id"];
	model: BackendModel;
	locals?: App.Locals;
	webSearch?: WebSearch;
	preprompt?: string;
	files?: File[];
	continue?: boolean;
}

export async function buildPrompt({
	messages,
	model,
	webSearch,
	preprompt,
	id,
}: buildPromptOptions): Promise<string> {
	let modifiedMessages = [...messages];

	if (webSearch && webSearch.context) {
		// find index of the last user message
		const lastUsrMsgIndex = modifiedMessages.map((el) => el.from).lastIndexOf("user");

		// combine all the other previous questions into one string
		const previousUserMessages = modifiedMessages.filter((el) => el.from === "user").slice(0, -1);
		const previousQuestions =
			previousUserMessages.length > 0
				? `Previous questions: \n${previousUserMessages
						.map(({ content }) => `- ${content}`)
						.join("\n")}`
				: "";

		const currentDate = format(new Date(), "MMMM d, yyyy");

		// update the last user message directly (that way if the last message is an assistant partial answer, we keep the beginning of that answer)
		modifiedMessages[lastUsrMsgIndex] = {
			from: "user",
			content: `I searched the web using the query: ${webSearch.searchQuery}. Today is ${currentDate} and here are the results:
=====================
${webSearch.context}
=====================
${previousQuestions}
Answer the question: ${messages[lastUsrMsgIndex].content}`,
		};
	}
	// section to handle potential files input
	if (model.multimodal) {
		modifiedMessages = await Promise.all(
			modifiedMessages.map(async (el) => {
				let content = el.content;

				if (el.from === "user") {
					if (el?.files && el.files.length > 0 && id) {
						const markdowns = await Promise.all(
							el.files.map(async (hash) => {
								try {
									const { content: image, mime } = await downloadFile(hash, id);
									const b64 = image.toString("base64");
									return `![](data:${mime};base64,${b64})})`;
								} catch (e) {
									console.error(e);
								}
							})
						);
						content += markdowns.join("\n ");
					} else {
						// if no image, append an empty white image
						content +=
							"\n![](data:image/png;base64,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)";
					}
				}

				return { ...el, content };
			})
		);
	}

	return (
		model
			.chatPromptRender({ messages: modifiedMessages, preprompt })
			// Not super precise, but it's truncated in the model's backend anyway
			.split(" ")
			.slice(-(model.parameters?.truncate ?? 0))
			.join(" ")
	);
}