async function update()

in src/routes/conversation/[id]/+server.ts [342:436]
69 lines of code
18 McCabe index (conditional complexity)

			async function update(event: MessageUpdate) {
				if (!messageToWriteTo || !conv) {
					throw Error("No message or conversation to write events to");
				}

				// Add token to content or skip if empty
				if (event.type === MessageUpdateType.Stream) {
					if (event.token === "") return;
					messageToWriteTo.content += event.token;

					// add to token total
					MetricsServer.getMetrics().model.tokenCountTotal.inc({ model: model?.id });

					// if this is the first token, add to time to first token
					if (!lastTokenTimestamp) {
						MetricsServer.getMetrics().model.timeToFirstToken.observe(
							{ model: model?.id },
							Date.now() - promptedAt.getTime()
						);
						lastTokenTimestamp = new Date();
					}

					// add to time per token
					MetricsServer.getMetrics().model.timePerOutputToken.observe(
						{ model: model?.id },
						Date.now() - (lastTokenTimestamp ?? promptedAt).getTime()
					);
					lastTokenTimestamp = new Date();
				} else if (
					event.type === MessageUpdateType.Reasoning &&
					event.subtype === MessageReasoningUpdateType.Stream
				) {
					messageToWriteTo.reasoning ??= "";
					messageToWriteTo.reasoning += event.token;
				}

				// Set the title
				else if (event.type === MessageUpdateType.Title) {
					conv.title = event.title;
					await collections.conversations.updateOne(
						{ _id: convId },
						{ $set: { title: conv?.title, updatedAt: new Date() } }
					);
				}

				// Set the final text and the interrupted flag
				else if (event.type === MessageUpdateType.FinalAnswer) {
					messageToWriteTo.interrupted = event.interrupted;
					messageToWriteTo.content = initialMessageContent + event.text;

					// add to latency
					MetricsServer.getMetrics().model.latency.observe(
						{ model: model?.id },
						Date.now() - promptedAt.getTime()
					);
				}

				// Add file
				else if (event.type === MessageUpdateType.File) {
					messageToWriteTo.files = [
						...(messageToWriteTo.files ?? []),
						{ type: "hash", name: event.name, value: event.sha, mime: event.mime },
					];
				}

				// Append to the persistent message updates if it's not a stream update
				if (
					event.type !== MessageUpdateType.Stream &&
					!(
						event.type === MessageUpdateType.Status &&
						event.status === MessageUpdateStatus.KeepAlive
					) &&
					!(
						event.type === MessageUpdateType.Reasoning &&
						event.subtype === MessageReasoningUpdateType.Stream
					)
				) {
					messageToWriteTo?.updates?.push(event);
				}

				// Avoid remote keylogging attack executed by watching packet lengths
				// by padding the text with null chars to a fixed length
				// https://cdn.arstechnica.net/wp-content/uploads/2024/03/LLM-Side-Channel.pdf
				if (event.type === MessageUpdateType.Stream) {
					event = { ...event, token: event.token.padEnd(16, "\0") };
				}

				// Send the update to the client
				controller.enqueue(JSON.stringify(event) + "\n");

				// Send 4096 of spaces to make sure the browser doesn't blocking buffer that holding the response
				if (event.type === MessageUpdateType.FinalAnswer) {
					controller.enqueue(" ".repeat(4096));
				}
			}