//
//  LobbyZipUpgrader.swift
//  ylgamehall
//
//  H5 zip 升级：下载远端 game_zip → 临时目录解压 → 原子 rename 到 lobbyRoot。
//  详见 docs/Development-Plan.md ADR-008-G / Design §6.3.4 / msext NewRootVC.m:1789-1869。
//

import Foundation
import ZIPFoundation

public actor LobbyZipUpgrader {

    public static let shared = LobbyZipUpgrader()

    public enum Outcome: Sendable {
        /// 本地版本已是最新（含远端 gameZip 为空 / 版本号未提升的情况），未做任何下载
        case noop
        /// 完成升级。`from → to` 是版本号变化。
        case upgraded(from: Int, to: Int)
    }

    public enum UpgradeError: Error, Sendable {
        case badGameZipURL(String)
        case downloadFailed(any Error)
        case httpStatus(Int)
        case unzipFailed(any Error)
        case stagingMoveFailed(any Error)
    }

    private let session: URLSession

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

    /// 默认 URLSession：下载用 60s 超时（zip 大约 11 MB，4G 网络约 10s）。
    nonisolated public static var defaultSession: URLSession {
        let cfg = URLSessionConfiguration.default
        cfg.timeoutIntervalForRequest = 60
        cfg.timeoutIntervalForResource = 300
        return URLSession(configuration: cfg)
    }

    /// 比较远端 game_version 与本地 version.xml。需要升级则下载 + 解压 + 原子 rename。
    ///
    /// - Parameter resolved: VersionResolver.resolve(...) 的结果
    /// - Returns: `.noop` 已是最新；`.upgraded(from:to:)` 完成升级
    public func upgradeIfNeeded(resolved: ResolvedVersion) async throws -> Outcome {
        let localGameVersion = LocalVersionReader.localGameVersion
        guard resolved.gameVersion > localGameVersion,
              let zipURLString = resolved.gameZip,
              let zipURL = URL(string: zipURLString)
        else {
            return .noop
        }

        // 1. 下载到 tmp（URLSession 默认管理临时位置）
        let downloadedURL: URL
        let response: URLResponse
        do {
            (downloadedURL, response) = try await session.download(from: zipURL)
        } catch {
            throw UpgradeError.downloadFailed(error)
        }
        if let http = response as? HTTPURLResponse,
           !(200..<300).contains(http.statusCode) {
            throw UpgradeError.httpStatus(http.statusCode)
        }

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

        // 3. 原子 rename：删旧 lobbyRoot → 把 staging 移到位
        //    （msext "removeItem + ZipArchive overWrite:YES" 半途崩溃留半残；
        //     我们 staging 完整解压后再 rename，半途崩溃只留 staging，下次启动可清）
        let lobbyRoot = SandboxPaths.lobbyRoot
        do {
            if fm.fileExists(atPath: lobbyRoot.path) {
                try fm.removeItem(at: lobbyRoot)
            }
            // 父目录确保存在（Library/Caches 永远存在，无需创建中间路径）
            try fm.moveItem(at: staging, to: lobbyRoot)
        } catch {
            try? fm.removeItem(at: staging)
            throw UpgradeError.stagingMoveFailed(error)
        }

        return .upgraded(from: localGameVersion, to: resolved.gameVersion)
    }
}