/** @file switchboard: Flower-style egress handles, served over Cap'n Web. */
import { WorkerEntrypoint } from "cloudflare:workers";
import { RpcTarget, newWorkersRpcResponse } from "capnweb";
import { checkUrl, mergeLabels } from "./labels.js";

/**
 * One egress handle: reaches only URLs within its labels, through the
 * network its `network` label names. Like a Flower switchboard handle, it
 * can only be narrowed; unlike one, it is a Cap'n Web stub, not an fd.
 */
export class Handle extends RpcTarget {
	#labels;
	#net;

	/**
	 * @param {Record<string, string>} labels
	 * @param {Fetcher} net
	 */
	constructor(labels, net) {
		super();
		this.#labels = labels;
		this.#net = net;
	}

	/** @param {Record<string, string>} more */
	constrain(more) {
		return new Handle(mergeLabels(this.#labels, more), this.#net);
	}

	labels() {
		return this.#labels;
	}

	/** @param {Request} request */
	fetch(request) {
		checkUrl(this.#labels, request.url);
		return this.#net.fetch(request);
	}

	/**
	 * Open a WebSocket to `url`; its messages cross the session as streams.
	 *
	 * @param {string} url `http:` or `https:`, as for a `fetch` upgrade
	 * @param {string[]} [protocols]
	 */
	async webSocket(url, protocols = []) {
		checkUrl(this.#labels, url);
		const headers = { Upgrade: "websocket" };
		if (protocols.length) headers["Sec-WebSocket-Protocol"] = protocols.join(", ");
		const resp = await this.#net.fetch(url, { headers });
		const ws = resp.webSocket;
		if (!ws) throw new Error(`no websocket: ${resp.status}`);
		ws.accept();
		const readable = new ReadableStream({
			start(controller) {
				ws.addEventListener("message", (e) => controller.enqueue(e.data));
				ws.addEventListener("close", () => controller.close());
				ws.addEventListener("error", () => controller.error(new Error("websocket error")));
			},
		});
		const writable = new WritableStream({
			write: (chunk) => ws.send(chunk),
			close: () => ws.close(),
			abort: () => ws.close(1011),
		});
		return { readable, writable, protocol: resp.headers.get("Sec-WebSocket-Protocol") ?? "" };
	}
}

/**
 * A switchboard socket: a WebSocket upgrade here starts a Cap'n Web
 * session whose main object is a {@link Handle} with this socket's labels.
 */
export default class Root extends WorkerEntrypoint {
	fetch(request) {
		const labels = Object.freeze({ ...this.ctx.props });
		const net = { public: this.env.PUBLIC, local: this.env.LOCAL }[labels.network];
		if (!net) return new Response("socket has no network\n", { status: 500 });
		return newWorkersRpcResponse(request, new Handle(labels, net));
	}
}