import SwiftUI
import UIKit
import UniformTypeIdentifiers

// Share Extension 主控制器：把 share sheet 传入的文件拷进 App Group 收件箱，再以**品牌引导界面**
// （ShareGuideView：吉祥物 + 字标 + 已就绪文件数 + 「打开 Commilitia Drop」按钮）引导用户回到主 app
// 选设备发送（扩展只交接、不跑引擎，避 120MB jetsam，见 PLAN §I5）。
//
// 为何是「引导」而非自动跳：iOS 不官方支持、也不可靠地允许 share 扩展自动拉起宿主 app（旧单参
// openURL: 自 iOS 10 弃用、iOS 18+ 已成空壳）。故改为明确的用户操作：点「打开」尝试唤起（响应链经
// IMP 调现代 open，最大努力）。无论唤起成败，文件已落 App Group 收件箱，用户回到 app 时
// CDropApp.scenePhase(.active)→loadPendingShares 即弹发送预览，故分享始终能用、不丢文件。
final class ShareViewController: UIViewController
{
    private let model = ShareModel()
    private var started = false
    // 已暂存文件的目标 URL（取消时据此删掉收件箱里的它们，不残留）。
    private var stagedURLs: [URL] = []

    override func viewDidLoad()
    {
        super.viewDidLoad()
        let host = UIHostingController(
            rootView: ShareGuideView(
                model: model,
                onOpen: { [weak self] in self?.openAndFinish() },
                onCancel: { [weak self] in self?.cancelAndFinish() }))
        addChild(host)
        host.view.frame = view.bounds
        host.view.autoresizingMask = [ .flexibleWidth, .flexibleHeight ]
        view.addSubview(host.view)
        host.didMove(toParent: self)
    }

    override func viewDidAppear(_ animated: Bool)
    {
        super.viewDidAppear(animated)
        guard !started else { return }   // viewDidAppear 可能多次；只处理一次
        started = true
        Task { await stageAll() }
    }

    private func stageAll() async
    {
        let items = (extensionContext?.inputItems as? [NSExtensionItem]) ?? []
        var urls: [URL] = []
        for item in items
        {
            for provider in item.attachments ?? []
            {
                if let dest = await stage(provider) { urls.append(dest) }
            }
        }
        stagedURLs = urls
        await MainActor.run { model.fileCount = urls.count }
    }

    // 「打开 Commilitia Drop」：尝试唤起主 app（最大努力），延后 completeRequest 给系统留出拉起窗口
    // （立即 completeRequest 会拆掉扩展进程、可能取消尚未真正开始的唤起）。文件留在收件箱供主 app 接手。
    private func openAndFinish()
    {
        if let url = URL(string: "commilitia-drop://share") { openViaResponder(url) }
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.35)
        { [weak self] in
            self?.extensionContext?.completeRequest(returningItems: nil)
        }
    }

    // 「取消」：删掉刚暂存进收件箱的文件（不残留、避免下次开 app 误弹预览），返回来源 app。
    private func cancelAndFinish()
    {
        for url in stagedURLs
        {
            try? FileManager.default.removeItem(at: url.deletingLastPathComponent())
        }
        extensionContext?.completeRequest(returningItems: nil)
    }

    // 把单个附件落到 App Group 收件箱，返回落地 URL。优先文件表示（大文件不整体进内存），失败退数据表示
    // （仅提供数据、无文件表示的提供者）。两路都失败返回 nil。
    private func stage(_ provider: NSItemProvider) async -> URL?
    {
        if let u = await stageFile(provider) { return u }
        return await stageData(provider)
    }

    private func stageFile(_ provider: NSItemProvider) async -> URL?
    {
        let typeId = provider.registeredTypeIdentifiers.first ?? UTType.item.identifier
        return await withCheckedContinuation
        { cont in
            provider.loadFileRepresentation(forTypeIdentifier: typeId)
            { url, _ in
                guard let url, let dest = AppGroup.stagedDestination(originalName: url.lastPathComponent)
                else { cont.resume(returning: nil); return }
                do
                {
                    try FileManager.default.copyItem(at: url, to: dest)
                    cont.resume(returning: dest)
                }
                catch
                {
                    cont.resume(returning: nil)
                }
            }
        }
    }

    private func stageData(_ provider: NSItemProvider) async -> URL?
    {
        let typeId = provider.registeredTypeIdentifiers.first ?? UTType.data.identifier
        let name = suggestedName(provider, typeId: typeId)
        return await withCheckedContinuation
        { cont in
            provider.loadDataRepresentation(forTypeIdentifier: typeId)
            { data, _ in
                guard let data, let dest = AppGroup.stagedDestination(originalName: name)
                else { cont.resume(returning: nil); return }
                do
                {
                    try data.write(to: dest)
                    cont.resume(returning: dest)
                }
                catch
                {
                    cont.resume(returning: nil)
                }
            }
        }
    }

    // 数据兜底路径的文件名：优先提供者建议名，否则按类型首选扩展名拼一个。
    private func suggestedName(_ provider: NSItemProvider, typeId: String) -> String
    {
        if let s = provider.suggestedName, !s.isEmpty
        {
            if (s as NSString).pathExtension.isEmpty,
               let ext = UTType(typeId)?.preferredFilenameExtension
            {
                return "\(s).\(ext)"
            }
            return s
        }
        let ext = UTType(typeId)?.preferredFilenameExtension ?? "dat"
        return "shared-\(UUID().uuidString.prefix(8)).\(ext)"
    }

    // 沿响应链找 UIApplication 实例，经 IMP 调现代 open(_:options:completionHandler:)（绕过扩展对
    // UIApplication 的编译期可用性限制）。找不到则退旧单参 openURL:（iOS 18+ 多为空壳，仅历史兜底）。
    private func openViaResponder(_ url: URL)
    {
        let modern = NSSelectorFromString("openURL:options:completionHandler:")
        var responder: UIResponder? = self
        while let r = responder
        {
            if r.responds(to: modern), let app = r as? NSObject,
               let method = class_getInstanceMethod(type(of: app), modern)
            {
                typealias OpenFn = @convention(c) (NSObject, Selector, NSURL, NSDictionary, Any?) -> Void
                let fn = unsafeBitCast(method_getImplementation(method), to: OpenFn.self)
                fn(app, modern, url as NSURL, NSDictionary(), nil)
                return
            }
            responder = r.next
        }
        let legacy = NSSelectorFromString("openURL:")
        responder = self
        while let r = responder
        {
            if r.responds(to: legacy) { _ = r.perform(legacy, with: url); return }
            responder = r.next
        }
    }
}