// ==UserScript==
// @name         ChatGPT Model Switcher
// @namespace    https://ucm.dev/
// @version      1.0
// @description  Switch ChatGPT model mid-chat
// @author       GPT-4, GPT-3.5, Copilot, and Sam Watkins <sam@ucm.dev>
// @match        *://chat.openai.com/*
// @grant        none
// @license      MIT
// @downloadURL https://update.greasyfork.icu/scripts/463362/ChatGPT%20Model%20Switcher.user.js
// @updateURL https://update.greasyfork.icu/scripts/463362/ChatGPT%20Model%20Switcher.meta.js
// ==/UserScript==

// This user script adds a model switcher to the OpenAI chat interface,
// allowing users to switch between different AI models when conversing.

(function () {

	"use strict";

	// Define various constants, such as available models,
	// URLs for API calls, messages, and selectors for DOM elements.

	const MODELS = [
		{
			"name": "text-davinci-002-render-sha",
			"label": "Default (GPT-3.5)"
		},
		{
			"name": "text-davinci-002-render-paid",
			"label": "Legacy (GPT-3.5)"
		},
		{
			"name": "gpt-4",
			"label": "GPT-4"
		}
	];

	const URLS = {
		conversation: "https://chat.openai.com/backend-api/conversation",
	};

	const MESSAGES = {
		modelUnavailable: "The previous model used in this conversation is unavailable. " +
		"We've switched you to the latest default model",
		modelChanged: "Now using ",
	};

	const SELECTORS = {
		buttons: "#__next main form > div div:nth-of-type(1)",
		messagesContainer: ".flex-col.items-center",
		modelUnavailableMessage: ".flex-col.items-center .text-center",
		chatGPTModelSelect: "#__next button[data-headlessui-state]",
	};

	const IDS = {
		switcher: "chatgpt-model-switcher",
	};

	// Utility functions
	const $ = (selector) => document.querySelector(selector);
	const $$ = (selector) => document.querySelectorAll(selector);
	const $id = (id) => document.getElementById(id);
	const $create = (element) => document.createElement(element);

	// Update the model parameter in the request body to match the
	// selected model in the UI.
	function updateModelParameter(originalRequest) {
		// Parse the request body
		const requestData = JSON.parse(originalRequest.body);

		// Make sure the request has a model parameter
		if (!requestData.model) return originalRequest;

		// Make sure the model switcher exists in the UI
		const modelSwitcher = $id(IDS.switcher);
		if (!modelSwitcher) return originalRequest;

		// Update the model parameter based on the selected option in the UI
		requestData.model = modelSwitcher.value;

		// Modify the request to include the updated model parameter
		const updatedRequest = {
			...originalRequest,
			body: JSON.stringify(requestData),
		};

		return updatedRequest;
	}

	// Check if the request is a conversation request.
	function isConversationRequest(requestArgs) {
		return	requestArgs[0] &&
		requestArgs[0] === URLS.conversation &&
		requestArgs[1] &&
		requestArgs[1].method === "POST" &&
		requestArgs[1].body;
	}

	// Replace the original fetch function with a new function that
	// updates the model parameter in the request before sending it.
	const originalFetch = window.fetch;
	window.fetch = async function () {
		if (isConversationRequest(arguments)) {
			arguments[1] = updateModelParameter(arguments[1]);
		}
		return await originalFetch.apply(this, arguments);
	};

	// Replace the model unavailable message with a message indicating
	// that the model has been changed.
	function replaceModelUnavailableMessage() {
		for (const element of $$(SELECTORS.modelUnavailableMessage)) {
			if (element.textContent !== MESSAGES.modelUnavailable) continue;
			const newModel = $id(IDS.switcher).value;
			const newModelLabel = MODELS.find((model) => model.name === newModel).label;
			element.textContent = MESSAGES.modelChanged + newModelLabel;
		}
	}

	// Synchronize the custom model switcher with the original model selector.
	// Update the custom model switcher's value to match the currently selected
	// model in the original model selector.
	function syncCustomModelSwitcher() {
		const chatGPTModelSelect = $(SELECTORS.chatGPTModelSelect);
		const modelLabel = chatGPTModelSelect.innerText.split("\n")[1];
		const customModelSwitcher = $id(IDS.switcher);

		for (const model of MODELS) {
			if (model.label !== modelLabel) continue;
			customModelSwitcher.value = model.name;
			break;
		}
	}

	// Initialize the model switcher: Add it to the chat interface, watch the
	// original model selector, and watch for the model unavailable message.
	function initModelSwitcher() {
		if ($id(IDS.switcher)) return;

		const buttons = $(SELECTORS.buttons);

		// Create the model switcher
		const modelSwitcher = $create("select");
		modelSwitcher.id = IDS.switcher;
		modelSwitcher.classList.add("btn", "flex", "gap-2", "justify-center", "btn-neutral");
		for (const model of MODELS) {
			const option = $create("option");
			option.value = model.name;
			option.textContent = model.label;
			modelSwitcher.appendChild(option);
		}

		// Add the model switcher to the button bar
		buttons.appendChild(modelSwitcher);

		// Initialize a MutationObserver to watch the messages container
		for (const element of $$(SELECTORS.messagesContainer)) {
			new MutationObserver(replaceModelUnavailableMessage).observe(element, { childList: true, subtree: true });
		}
	}

	let chatGPTModelSelectObserver = null;

	// Watch ChatGPT's model selector
	function watchChatGPTModelSelect() {
		if (chatGPTModelSelectObserver) return;
		const chatGPTModelSelect = $(SELECTORS.chatGPTModelSelect);
		chatGPTModelSelectObserver = new MutationObserver(syncCustomModelSwitcher);
		chatGPTModelSelectObserver.observe(chatGPTModelSelect, { childList: true, characterData: true, subtree: true });
	}

	// Check if the chat interface has been loaded, and call the
	// initModelSwitcher function when it is detected.
	function chatInterfaceChanged() {
		if ($(SELECTORS.buttons) && $(SELECTORS.messagesContainer)) {
			initModelSwitcher();
		}
		if ($(SELECTORS.chatGPTModelSelect)) {
			watchChatGPTModelSelect();
		}
	}

	// Observe mutations to the body element, and call the
	// initModelSwitcher function when the chat interface is detected.
	new MutationObserver(chatInterfaceChanged).observe(document.body, { childList: true, subtree: true });

})();