'use strict';

// Retry an async function with exponential backoff up to a max delay.
// No attempt limit: keeps retrying on transient failures forever.
// Transient = network errors, 5xx, 429. 4xx client errors are NOT retried by default.
const TRANSIENT_NETWORK_CODES = new Set([
	'ECONNREFUSED', 'ECONNRESET', 'ETIMEDOUT', 'EAI_AGAIN',
	'ENOTFOUND', 'EPIPE', 'ERR_SOCKET_TIMEOUT', 'ETIMEOUT',
]);

function isRetryable(error){
	// Network / DNS / socket errors
	if(error && error.code && TRANSIENT_NETWORK_CODES.has(error.code)) return true;

	// HTTP status codes worth retrying
	let status = Number(error && error.status) || Number(error && error.status_code);
	if(status >= 500 && status < 600) return true;
	if(status === 429) return true;
	if(status === 502 || status === 503 || status === 504) return true;

	// ResponseError from the ollama package carries status_code
	if(error && error.name === 'ResponseError' && status >= 500) return true;

	return false;
}

async function sleep(ms){
	return new Promise(resolve => setTimeout(resolve, ms));
}

async function withRetry(fn, options = {}){
	let baseDelay = options.baseDelay || 1000;
	let maxDelay = options.maxDelay || 30000;
	let multiplier = options.multiplier || 2;
	let jitter = options.jitter || 0.2;
	let label = options.label || 'operation';
	let shouldRetry = options.shouldRetry || isRetryable;

	let attempt = 0;
	let delay = baseDelay;

	while(true){
		try{
			return await fn();
		}catch(error){
			attempt++;
			if(!shouldRetry(error)){
				console.error(`${label} attempt ${attempt} failed permanently:`, error.message);
				throw error;
			}

			console.error(`${label} attempt ${attempt} failed, retrying in ${delay}ms:`, error.message);
			let jittered = Math.round(delay * (1 + (Math.random() * 2 - 1) * jitter));
			await sleep(jittered);
			delay = Math.min(delay * multiplier, maxDelay);
		}
	}
}

// Convenience: retry a fetch call. On success returns the Response.
async function fetchWithRetry(url, options = {}, retryOptions = {}){
	return await withRetry(async () => {
		let res = await fetch(url, options);
		if(!res.ok){
			let error = new Error(`UpstreamError`);
			error.message = `Request to ${url.split('?')[0]} failed( ${res.status})`;
			error.status = res.status;
			throw error;
		}
		return res;
	}, { label: `fetch ${url.split('?')[0]}`, ...retryOptions });
}

// Convenience: retry a fetch call and parse JSON response.
async function fetchJSONWithRetry(url, options = {}, retryOptions = {}){
	let res = await fetchWithRetry(url, options, retryOptions);
	return await res.json();
}

module.exports = {
	withRetry,
	fetchWithRetry,
	fetchJSONWithRetry,
	isRetryable,
};