import type { Peer } from "../../peer.js";
import { Decoder, Encoder } from "cbor-x";
import { StreamConnection } from "./StreamConnection.js";

const NullValue = Symbol.for(null);

function concatUint8Array(buffer1: Uint8Array, buffer2: Uint8Array) {
	const tmp = new Uint8Array(buffer1.byteLength + buffer2.byteLength);
	tmp.set(buffer1, 0);
	tmp.set(buffer2, buffer1.byteLength);
	return new Uint8Array(tmp.buffer);
}

const iterateOver = async function* (stream: ReadableStream) {
	const reader = stream.getReader();
	try {
		while (true) {
			const { done, value } = await reader.read();
			if (done) return;
			yield value;
		}
	} finally {
		reader.releaseLock();
	}
};

export class Cbor extends StreamConnection {
	readonly serialization = "Cbor";
	private _encoder = new Encoder();
	private _decoder = new Decoder();
	private _inc;
	private _decoderStream = new TransformStream<ArrayBuffer, unknown>({
		transform: (abchunk, controller) => {
			let chunk = new Uint8Array(abchunk);
			if (this._inc) {
				chunk = concatUint8Array(this._inc, chunk);
				this._inc = null;
			}
			let values;
			try {
				values = this._decoder.decodeMultiple(chunk);
			} catch (error) {
				if (error.incomplete) {
					this._inc = chunk.subarray(error.lastPosition);
					values = error.values;
				} else throw error;
			} finally {
				for (let value of values || []) {
					if (value === null) value = NullValue;
					controller.enqueue(value);
				}
			}
		},
	});

	constructor(peerId: string, provider: Peer, options: any) {
		super(peerId, provider, { ...options, reliable: true });

		void this._rawReadStream.pipeTo(this._decoderStream.writable);

		(async () => {
			for await (const msg of iterateOver(this._decoderStream.readable)) {
				if (msg.__peerData?.type === "close") {
					this.close();
					return;
				}
				this.emit("data", msg);
			}
		})();
	}

	protected override _send(data) {
		return this.writer.write(this._encoder.encode(data));
	}
}