import Foundation

/// Intercepts every request made through a `URLSession` configured with it,
/// so network-dependent code (`ApiClient`, `ApiService`,
/// `FeatureControlService`, ...) can be unit tested without touching a real
/// server. Register a handler per test, then build a session via
/// `URLProtocolStub.makeSession()`.
final class URLProtocolStub: URLProtocol {
    /// `nonisolated(unsafe)`: `URLProtocol` subclasses are instantiated and
    /// driven by URLSession's own internal (non-Sendable-checked) machinery,
    /// off the calling actor. Tests only ever set this once, synchronously,
    /// before starting the request that reads it.
    nonisolated(unsafe) static var handler: ((URLRequest) throws -> (HTTPURLResponse, Data))?

    static func makeSession() -> URLSession {
        let config = URLSessionConfiguration.ephemeral
        config.protocolClasses = [URLProtocolStub.self]
        return URLSession(configuration: config)
    }

    override class func canInit(with request: URLRequest) -> Bool { true }
    override class func canonicalRequest(for request: URLRequest) -> URLRequest { request }

    override func startLoading() {
        guard let handler = URLProtocolStub.handler else {
            client?.urlProtocol(self, didFailWithError: URLError(.badServerResponse))
            return
        }
        do {
            let (response, data) = try handler(request)
            client?.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
            client?.urlProtocol(self, didLoad: data)
            client?.urlProtocolDidFinishLoading(self)
        } catch {
            client?.urlProtocol(self, didFailWithError: error)
        }
    }

    override func stopLoading() {}
}

extension HTTPURLResponse {
    static func stub(url: URL = URL(string: "https://example.com")!, statusCode: Int) -> HTTPURLResponse {
        HTTPURLResponse(url: url, statusCode: statusCode, httpVersion: nil, headerFields: nil)!
    }
}