//
//  SubGameDownloader.swift
//  ylgamehall
//
//  子游戏 zip 下载 + 解压：与 msext gameController.m:1340-1401 等价。
//    - 缓存命中（`{Caches}/{gameDir}/{gameStart}/index.html` 已在）→ 直接复用
//    - 缓存未命中 → URLSession 下载 → 解压到 staging → 原子 rename
//
//  与 LobbyZipUpgrader 思路一致；不复用是因为目录路径/版本判定/缓存策略不同
//  （子游戏只看是否存在，不比版本号；msext 子游戏升级走另一条 uplevel 路径，
//  本项目暂未接入 — 待业务确认远端是否真有 sub-game 版本下发）。
//
//  详见 docs/Development-Plan.md §5.6 / §6.7。
//

import Foundation
import ZIPFoundation

public actor SubGameDownloader {

    public static let shared = SubGameDownloader()

    public enum Outcome: Sendable {
        /// 缓存命中，未下载
        case alreadyExists
        /// 完成下载 + 解压（zipBytes 为下载字节数，便于日志 / 测试）
        case downloaded(zipBytes: Int64)
    }

    public enum DownloadError: Error, Sendable {
        case missingDownloadURL
        case badDownloadURL(String)
        case downloadFailed(any Error)
        case httpStatus(Int)
        case unzipFailed(any Error)
        case stagingMoveFailed(any Error)
    }

    private let session: URLSession

    public init(session: URLSession = SubGameDownloader.defaultSession) {
        self.session = session
    }

    nonisolated public static var defaultSession: URLSession {
        let cfg = URLSessionConfiguration.default
        cfg.timeoutIntervalForRequest = 60
        cfg.timeoutIntervalForResource = 300
        return URLSession(configuration: cfg)
    }

    /// 确保 `{Caches}/{request.gameDir}/{request.gameStart}/index.html` 已就绪。
    ///
    /// - Parameters:
    ///   - request: SwitchOverGameData 解出的入参
    ///   - onProgress: 0…1 进度，URLSession delegate 后台线程派发；UI 层负责 hop MainActor
    /// - Returns: `.alreadyExists` 命中缓存；`.downloaded(zipBytes:)` 完成下载
    public func ensureReady(
        request: SubGameRequest,
        onProgress: @escaping @Sendable (Double) -> Void = { _ in }
    ) async throws -> Outcome {
        let fm = FileManager.default
        let indexPath = SandboxPaths.subGameIndex(request.gameDir, request.gameStart).path
        if fm.fileExists(atPath: indexPath) {
            return .alreadyExists
        }

        guard !request.downloadURL.isEmpty else {
            throw DownloadError.missingDownloadURL
        }
        guard let zipURL = URL(string: request.downloadURL) else {
            throw DownloadError.badDownloadURL(request.downloadURL)
        }

        // 1. 下载到 tmp
        let progressDelegate = DownloadProgressDelegate(onProgress: onProgress)
        let downloadedURL: URL
        let response: URLResponse
        do {
            (downloadedURL, response) = try await session.download(
                from: zipURL,
                delegate: progressDelegate
            )
        } catch {
            throw DownloadError.downloadFailed(error)
        }
        if let http = response as? HTTPURLResponse,
           !(200..<300).contains(http.statusCode) {
            throw DownloadError.httpStatus(http.statusCode)
        }
        onProgress(1.0)

        let zipBytes = (try? fm.attributesOfItem(atPath: downloadedURL.path)[.size] as? NSNumber)?
            .int64Value ?? 0

        // 2. 解压到隔离 staging
        let staging = SandboxPaths.caches
            .appendingPathComponent("subgame-staging-\(UUID().uuidString)")
        do {
            try fm.createDirectory(at: staging, withIntermediateDirectories: true)
            try fm.unzipItem(at: downloadedURL, to: staging)
        } catch {
            try? fm.removeItem(at: staging)
            throw DownloadError.unzipFailed(error)
        }
        try? fm.removeItem(at: downloadedURL)

        // 3. 原子 rename：删旧 subGameRoot → 把 staging 移到位
        //    msext 行为：zip 内部已含 `{gameStart}/` 子目录，解压到 staging 后
        //    再整体 move 到 `{Caches}/{gameDir}/`，结果就是 `{gameDir}/{gameStart}/index.html`
        let subGameRoot = SandboxPaths.subGameRoot(request.gameDir)
        do {
            if fm.fileExists(atPath: subGameRoot.path) {
                try fm.removeItem(at: subGameRoot)
            }
            try fm.moveItem(at: staging, to: subGameRoot)
        } catch {
            try? fm.removeItem(at: staging)
            throw DownloadError.stagingMoveFailed(error)
        }

        return .downloaded(zipBytes: zipBytes)
    }
}

/// URLSession 下载进度桥接。
///
/// 与 LobbyZipUpgrader 同款实现就地复制（两处使用，不抽公共 — 三处出现时再合并）。
private final class DownloadProgressDelegate: NSObject,
                                              URLSessionDownloadDelegate,
                                              @unchecked Sendable {
    private let onProgress: @Sendable (Double) -> Void

    init(onProgress: @escaping @Sendable (Double) -> Void) {
        self.onProgress = onProgress
        super.init()
    }

    func urlSession(_ session: URLSession,
                    downloadTask: URLSessionDownloadTask,
                    didWriteData bytesWritten: Int64,
                    totalBytesWritten: Int64,
                    totalBytesExpectedToWrite: Int64) {
        guard totalBytesExpectedToWrite > 0 else { return }
        let p = Double(totalBytesWritten) / Double(totalBytesExpectedToWrite)
        onProgress(min(max(p, 0), 1))
    }

    func urlSession(_ session: URLSession,
                    downloadTask: URLSessionDownloadTask,
                    didFinishDownloadingTo location: URL) {
        // no-op
    }
}