app_for_reddit/Reddit App/Utilities/NetworkClient.swift

import Foundation

enum NetworkClient {
    static let session: URLSession = {
        let configuration = URLSessionConfiguration.default
        configuration.waitsForConnectivity = true
        configuration.timeoutIntervalForRequest = 60
        configuration.timeoutIntervalForResource = 120
        configuration.requestCachePolicy = .reloadIgnoringLocalCacheData
        return URLSession(configuration: configuration)
    }()

    static func data(for request: URLRequest, retries: Int = 2) async throws -> (Data, URLResponse) {
        var lastError: Error?

        for attempt in 0...retries {
            if attempt > 0 {
                try await Task.sleep(nanoseconds: UInt64(attempt) * 400_000_000)
            }

            do {
                return try await session.data(for: request)
            } catch let error as URLError where error.isTransientNetworkFailure {
                lastError = error
            } catch {
                throw error
            }
        }

        throw lastError ?? URLError(.unknown)
    }

    static func prepare() async {
        guard let url = URL(string: "https://api.openai.com") else { return }

        var request = URLRequest(url: url)
        request.httpMethod = "HEAD"
        request.timeoutInterval = 15
        _ = try? await session.data(for: request)
    }
}

private extension URLError {
    var isTransientNetworkFailure: Bool {
        switch code {
        case .networkConnectionLost,
             .notConnectedToInternet,
             .timedOut,
             .cannotConnectToHost,
             .dnsLookupFailed,
             .cannotFindHost,
             .internationalRoamingOff,
             .callIsActive:
            return true
        default:
            return false
        }
    }
}