export async function* streamResponse(
	response: Response,
): AsyncGenerator<string> {
	if (response.status !== 200) {
		throw new Error(await response.text());
	}

	if (!response.body) {
		throw new Error(`No response body returned.`);
	}

	const stream = response.body as any;

	const decoder = new TextDecoder("utf-8");

	for await (const chunk of stream) {
		yield decoder.decode(chunk);
	}
}

function parseDataLine(line: string): any {
	const json = line.startsWith("data: ")
		? line.slice("data: ".length)
		: line.slice("data:".length);

	try {
		const data = JSON.parse(json);
		if (data.error) {
			throw new Error(`Error streaming response: ${data.error}`);
		}

		return data;
	} catch (e) {
		throw new Error(`Malformed JSON sent from server: ${json}`);
	}
}

function parseSseLine(line: string): { done: boolean; data: any } {
	if (line.startsWith("data: [DONE]")) {
		return { done: true, data: undefined };
	} else if (line.startsWith("data:")) {
		return { done: false, data: parseDataLine(line) };
	} else if (line.startsWith(": ping")) {
		return { done: true, data: undefined };
	}
	return { done: false, data: undefined };
}

export async function* streamSse(response: Response): AsyncGenerator<any> {
	let buffer = "";
	for await (const value of streamResponse(response)) {
		buffer += value;

		let position;
		while ((position = buffer.indexOf("\n")) >= 0) {
			const line = buffer.slice(0, position);
			buffer = buffer.slice(position + 1);

			const { done, data } = parseSseLine(line);
			if (done) {
				break;
			}
			if (data) {
				yield data;
			}
		}
	}

	if (buffer.length > 0) {
		const { done, data } = parseSseLine(buffer);
		if (!done && data) {
			yield data;
		}
	}
}