// This file is auto-generated by @hey-api/openapi-ts

import type { Config } from "./types.gen";

export type ServerSentEventsOptions<TData = unknown> = Omit<RequestInit, "method"> &
	Pick<Config, "method" | "responseTransformer" | "responseValidator"> & {
		/**
		 * Fetch API implementation. You can use this option to provide a custom
		 * fetch instance.
		 *
		 * @default globalThis.fetch
		 */
		fetch?: typeof fetch;
		/**
		 * Implementing clients can call request interceptors inside this hook.
		 */
		onRequest?: (url: string, init: RequestInit) => Promise<Request>;
		/**
		 * Callback invoked when a network or parsing error occurs during streaming.
		 *
		 * This option applies only if the endpoint returns a stream of events.
		 *
		 * @param error The error that occurred.
		 */
		onSseError?: (error: unknown) => void;
		/**
		 * Callback invoked when an event is streamed from the server.
		 *
		 * This option applies only if the endpoint returns a stream of events.
		 *
		 * @param event Event streamed from the server.
		 * @returns Nothing (void).
		 */
		onSseEvent?: (event: StreamEvent<TData>) => void;
		serializedBody?: RequestInit["body"];
		/**
		 * Default retry delay in milliseconds.
		 *
		 * This option applies only if the endpoint returns a stream of events.
		 *
		 * @default 3000
		 */
		sseDefaultRetryDelay?: number;
		/**
		 * Maximum number of retry attempts before giving up.
		 */
		sseMaxRetryAttempts?: number;
		/**
		 * Maximum retry delay in milliseconds.
		 *
		 * Applies only when exponential backoff is used.
		 *
		 * This option applies only if the endpoint returns a stream of events.
		 *
		 * @default 30000
		 */
		sseMaxRetryDelay?: number;
		/**
		 * Optional sleep function for retry backoff.
		 *
		 * Defaults to using `setTimeout`.
		 */
		sseSleepFn?: (ms: number) => Promise<void>;
		url: string;
	};

export interface StreamEvent<TData = unknown> {
	data: TData;
	event?: string;
	id?: string;
	retry?: number;
}

export type ServerSentEventsResult<TData = unknown, TReturn = void, TNext = unknown> = {
	stream: AsyncGenerator<TData extends Record<string, unknown> ? TData[keyof TData] : TData, TReturn, TNext>;
};

export const createSseClient = <TData = unknown>({
	onRequest,
	onSseError,
	onSseEvent,
	responseTransformer,
	responseValidator,
	sseDefaultRetryDelay,
	sseMaxRetryAttempts,
	sseMaxRetryDelay,
	sseSleepFn,
	url,
	...options
}: ServerSentEventsOptions): ServerSentEventsResult<TData> => {
	let lastEventId: string | undefined;

	const sleep = sseSleepFn ?? ((ms: number) => new Promise((resolve) => setTimeout(resolve, ms)));

	const createStream = async function* () {
		let retryDelay: number = sseDefaultRetryDelay ?? 3000;
		let attempt = 0;
		const signal = options.signal ?? new AbortController().signal;

		while (true) {
			if (signal.aborted) break;

			attempt++;

			const headers =
				options.headers instanceof Headers
					? options.headers
					: new Headers(options.headers as Record<string, string> | undefined);

			if (lastEventId !== undefined) {
				headers.set("Last-Event-ID", lastEventId);
			}

			try {
				const requestInit: RequestInit = {
					redirect: "follow",
					...options,
					body: options.serializedBody,
					headers,
					signal,
				};
				let request = new Request(url, requestInit);
				if (onRequest) {
					request = await onRequest(url, requestInit);
				}
				// fetch must be assigned here, otherwise it would throw the error:
				// TypeError: Failed to execute 'fetch' on 'Window': Illegal invocation
				const _fetch = options.fetch ?? globalThis.fetch;
				const response = await _fetch(request);

				if (!response.ok) throw new Error(`SSE failed: ${response.status} ${response.statusText}`);

				if (!response.body) throw new Error("No body in SSE response");

				const reader = response.body.pipeThrough(new TextDecoderStream()).getReader();

				let buffer = "";

				const abortHandler = () => {
					try {
						reader.cancel();
					} catch {
						// noop
					}
				};

				signal.addEventListener("abort", abortHandler);

				try {
					while (true) {
						const { done, value } = await reader.read();
						if (done) break;
						buffer += value;

						const chunks = buffer.split("\n\n");
						buffer = chunks.pop() ?? "";

						for (const chunk of chunks) {
							const lines = chunk.split("\n");
							const dataLines: Array<string> = [];
							let eventName: string | undefined;

							for (const line of lines) {
								if (line.startsWith("data:")) {
									dataLines.push(line.replace(/^data:\s*/, ""));
								} else if (line.startsWith("event:")) {
									eventName = line.replace(/^event:\s*/, "");
								} else if (line.startsWith("id:")) {
									lastEventId = line.replace(/^id:\s*/, "");
								} else if (line.startsWith("retry:")) {
									const parsed = Number.parseInt(line.replace(/^retry:\s*/, ""), 10);
									if (!Number.isNaN(parsed)) {
										retryDelay = parsed;
									}
								}
							}

							let data: unknown;
							let parsedJson = false;

							if (dataLines.length) {
								const rawData = dataLines.join("\n");
								try {
									data = JSON.parse(rawData);
									parsedJson = true;
								} catch {
									data = rawData;
								}
							}

							if (parsedJson) {
								if (responseValidator) {
									await responseValidator(data);
								}

								if (responseTransformer) {
									data = await responseTransformer(data);
								}
							}

							onSseEvent?.({
								data,
								event: eventName,
								id: lastEventId,
								retry: retryDelay,
							});

							if (dataLines.length) {
								yield data as any;
							}
						}
					}
				} finally {
					signal.removeEventListener("abort", abortHandler);
					reader.releaseLock();
				}

				break; // exit loop on normal completion
			} catch (error) {
				// connection failed or aborted; retry after delay
				onSseError?.(error);

				if (sseMaxRetryAttempts !== undefined && attempt >= sseMaxRetryAttempts) {
					break; // stop after firing error
				}

				// exponential backoff: double retry each attempt, cap at 30s
				const backoff = Math.min(retryDelay * 2 ** (attempt - 1), sseMaxRetryDelay ?? 30000);
				await sleep(backoff);
			}
		}
	};

	const stream = createStream();

	return { stream };
};