import Testing
import Foundation
@testable import 康康

// MARK: - Mock 网络层

/// 按 URL 注册完整响应体,startLoading 时按请求的 Range header 自动切片返回(206)或全量(200)。
/// 每个测试用唯一 URL 注册自己的内容 → 测试间不会互相覆盖,无需依赖执行顺序或可见性。
final class MockURLProtocol: URLProtocol, @unchecked Sendable {
    private static let lock = NSLock()
    private static var bodies: [String: Data] = [:]

    static func register(_ url: URL, body: Data) {
        lock.lock(); defer { lock.unlock() }
        bodies[url.path] = body
    }
    static func reset() {
        lock.lock(); defer { lock.unlock() }
        bodies.removeAll()
    }
    private static func body(forPath path: String) -> Data? {
        lock.lock(); defer { lock.unlock() }
        return bodies[path]
    }

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

    override func startLoading() {
        guard let url = request.url, let full = Self.body(forPath: url.path) else {
            client?.urlProtocol(self, didFailWithError: URLError(.fileDoesNotExist))
            return
        }
        var data = full
        var status = 200
        var headers: [String: String] = [:]
        if let range = request.value(forHTTPHeaderField: "Range"),
           let start = Self.parseRangeStart(range), start <= full.count {
            data = Data(full.suffix(from: start))
            status = 206
            headers["Content-Range"] = "bytes \(start)-\(full.count - 1)/\(full.count)"
        }
        let response = HTTPURLResponse(
            url: url, statusCode: status, httpVersion: nil, headerFields: headers)!
        client?.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
        client?.urlProtocol(self, didLoad: data)
        client?.urlProtocolDidFinishLoading(self)
    }

    override func stopLoading() {}

    /// "bytes=2-" → 2
    private static func parseRangeStart(_ s: String) -> Int? {
        guard let eq = s.firstIndex(of: "="), let dash = s.firstIndex(of: "-") else { return nil }
        return Int(s[s.index(after: eq)..<dash])
    }
}

private func mockConfiguration() -> URLSessionConfiguration {
    let config = URLSessionConfiguration.ephemeral
    config.protocolClasses = [MockURLProtocol.self]
    return config
}

private func tempFile() -> URL {
    FileManager.default.temporaryDirectory
        .appendingPathComponent(UUID().uuidString, isDirectory: true)
        .appendingPathComponent("a.bin")
}

private func uniqueURL() -> URL {
    URL(string: "https://mock.test/\(UUID().uuidString).bin")!
}

// MARK: - DownloadState

struct DownloadStateTests {
    @Test func fractionZeroWhenTotalZero() {
        let s = DownloadState(phase: .idle, receivedBytes: 0, totalBytes: 0, bytesPerSecond: 0)
        #expect(s.fraction == 0)
    }

    @Test func fractionComputed() {
        let s = DownloadState(phase: .downloading, receivedBytes: 50, totalBytes: 200, bytesPerSecond: 0)
        #expect(s.fraction == 0.25)
    }
}

// MARK: - FileDownloader

/// 串行执行:这些测试共享全局 URLProtocol / URLSession 状态,并行会互相干扰。
@Suite(.serialized)
struct FileDownloaderTests {

    @Test func downloadsFileContent() async throws {
        let url = uniqueURL()
        MockURLProtocol.register(url, body: Data("hello".utf8))
        let dst = tempFile()
        defer { try? FileManager.default.removeItem(at: dst.deletingLastPathComponent()) }

        let dl = FileDownloader(configuration: mockConfiguration())
        try await dl.download(from: url, to: dst, expectedBytes: 5)

        #expect(try Data(contentsOf: dst) == Data("hello".utf8))
        #expect(!FileManager.default.fileExists(atPath: dst.appendingPathExtension("part").path))
    }

    @Test func resumesFromPartialFile() async throws {
        let url = uniqueURL()
        MockURLProtocol.register(url, body: Data("hello".utf8))
        let dst = tempFile()
        defer { try? FileManager.default.removeItem(at: dst.deletingLastPathComponent()) }
        // 预置已下载的一半,download 应从 offset 2 续传
        try FileManager.default.createDirectory(
            at: dst.deletingLastPathComponent(), withIntermediateDirectories: true)
        try Data("he".utf8).write(to: dst.appendingPathExtension("part"))

        let dl = FileDownloader(configuration: mockConfiguration())
        try await dl.download(from: url, to: dst, expectedBytes: 5)

        #expect(try Data(contentsOf: dst) == Data("hello".utf8))
    }

    @Test func throwsOnSizeMismatch() async throws {
        let url = uniqueURL()
        MockURLProtocol.register(url, body: Data("hi".utf8))  // 仅 2 字节,期望 5
        let dst = tempFile()
        defer { try? FileManager.default.removeItem(at: dst.deletingLastPathComponent()) }

        let dl = FileDownloader(configuration: mockConfiguration())
        await #expect(throws: (any Error).self) {
            try await dl.download(from: url, to: dst, expectedBytes: 5)
        }
        #expect(!FileManager.default.fileExists(atPath: dst.path))
    }
}
