//
//  WiredCameraTransferPipeline.swift
//  suixinkan
//

import Foundation

/// 有线传图上传编排器，负责管理本地照片的上传任务（不含 USB/OTG 相机连接）。
@MainActor
final class WiredCameraTransferPipeline {
    var onTasksUpdated: (([CameraTransferTask]) -> Void)?

    private(set) var tasks: [CameraTransferTask] = []
    private var uploadSink: (any CameraAssetUploadSink)?
    private var uploadEnabled = true
    private var downloadScope = CameraDownloadStorage.Scope(accountKey: "unscoped", albumID: 0)
    private var activeUploadAssetIDs: Set<String> = []
    private var autoUploadEligibleAssetIDs: Set<String> = []
    private var pendingDeferredNotifyTask: Task<Void, Never>?
    private var lastDeferredNotifyDate = Date.distantPast
    private var lastNotifiedProgressByAssetID: [String: Int] = [:]
    private let maxRetries = 3
    private let deferredNotifyInterval: TimeInterval = 0.15
    private let maxConcurrentUploads = 3
    private var isUIAttached = false
    /// 用户已从列表删除、不应再展示的 asset ID。
    private(set) var excludedAssetIDs: Set<String> = []

    /// 绑定 UI 回调。
    func attachToUI(onTasksUpdated: @escaping ([CameraTransferTask]) -> Void) {
        isUIAttached = true
        self.onTasksUpdated = onTasksUpdated
    }

    /// 页面离开：取消 UI 回调与进行中的上传通知。
    func detachFromUI() {
        guard isUIAttached else { return }
        isUIAttached = false
        pendingDeferredNotifyTask?.cancel()
        pendingDeferredNotifyTask = nil
        activeUploadAssetIDs.removeAll()
        onTasksUpdated = nil
    }

    /// 配置上传 Sink、自动上传开关与下载作用域。
    func configure(
        uploadSink: (any CameraAssetUploadSink)?,
        uploadEnabled: Bool,
        downloadScope: CameraDownloadStorage.Scope? = nil
    ) {
        self.uploadSink = uploadSink
        self.uploadEnabled = uploadEnabled
        if let downloadScope {
            self.downloadScope = downloadScope
        }
    }

    /// 重试所有失败的上传任务。
    func retryFailedUploads() async {
        guard uploadEnabled, uploadSink != nil else { return }
        let failedAssetIDs = tasks.filter { $0.status == .failed }.map(\.assetID)
        for index in tasks.indices where tasks[index].status == .failed {
            tasks[index].status = .downloaded
            tasks[index].errorMessage = nil
        }
        notify()
        await uploadAssets(withIDs: failedAssetIDs)
    }

    /// 手动上传指定 asset 列表。
    func uploadAssets(withIDs assetIDs: [String]) async {
        guard uploadSink != nil else { return }
        var seenAssetIDs: Set<String> = []
        let uniqueAssetIDs = assetIDs.filter { seenAssetIDs.insert($0).inserted }
        var currentIndex = 0
        while currentIndex < uniqueAssetIDs.count {
            let upperBound = min(currentIndex + maxConcurrentUploads, uniqueAssetIDs.count)
            let batch = uniqueAssetIDs[currentIndex ..< upperBound]
            let uploadTasks = batch.map { assetID in
                Task { @MainActor in
                    await self.uploadAssetIfNeeded(assetID: assetID)
                }
            }
            for task in uploadTasks {
                await task.value
            }
            currentIndex = upperBound
        }
    }

    /// 重传单张照片；若管道中无任务则根据本地相对路径恢复。
    func retryUpload(assetID: String, filename: String, localPath: String) async {
        guard uploadSink != nil else { return }
        guard !activeUploadAssetIDs.contains(assetID) else { return }

        if let index = tasks.firstIndex(where: { $0.assetID == assetID }) {
            if tasks[index].status == .uploaded { return }
            if tasks[index].localPath?.isEmpty != false, !localPath.isEmpty {
                tasks[index].localPath = localPath
            }
            tasks[index].status = .downloaded
            tasks[index].errorMessage = nil
        } else {
            guard !localPath.isEmpty,
                  let localURL = CameraDownloadStorage.resolveLocalURL(from: localPath),
                  FileManager.default.fileExists(atPath: localURL.path) else {
                return
            }
            tasks.insert(
                CameraTransferTask(
                    assetID: assetID,
                    filename: filename,
                    localPath: localPath,
                    capturedAt: CameraTransferTask.capturedAtString(forLocalPath: localPath),
                    status: .downloaded
                ),
                at: 0
            )
        }

        notify()
        await uploadTask(assetID: assetID)
    }

    /// 按 assetID 查找任务。
    func task(forAssetID assetID: String) -> CameraTransferTask? {
        tasks.first { $0.assetID == assetID }
    }

    /// 同步用户已删除的 asset ID，防止再次带回。
    func setExcludedAssetIDs(_ ids: Set<String>) {
        excludedAssetIDs = ids
    }

    /// 从管道移除 asset。
    func removeAsset(assetID: String) {
        guard !assetID.isEmpty else { return }
        excludedAssetIDs.insert(assetID)
        tasks.removeAll { $0.assetID == assetID }
        autoUploadEligibleAssetIDs.remove(assetID)
        activeUploadAssetIDs.remove(assetID)
        lastNotifiedProgressByAssetID.removeValue(forKey: assetID)
    }

    /// 将相机已下载到本地的照片纳入传输管道。
    func ingestDownloadedAsset(
        assetID: String,
        filename: String,
        localPath: String,
        capturedAt: Date?,
        autoUpload: Bool
    ) {
        guard !excludedAssetIDs.contains(assetID) else { return }

        let capturedAtString = capturedAt.map { CameraTransferTask.capturedAtString(from: $0) }
            ?? CameraTransferTask.capturedAtString(forLocalPath: localPath)

        if let index = tasks.firstIndex(where: { $0.assetID == assetID }) {
            tasks[index].localPath = localPath
            if tasks[index].capturedAt?.isEmpty != false {
                tasks[index].capturedAt = capturedAtString
            }
            if tasks[index].status != .uploaded {
                tasks[index].status = .downloaded
            }
            tasks[index].errorMessage = nil
        } else {
            tasks.insert(
                CameraTransferTask(
                    assetID: assetID,
                    filename: filename,
                    localPath: localPath,
                    capturedAt: capturedAtString,
                    status: .downloaded
                ),
                at: 0
            )
        }

        if autoUpload, uploadEnabled, uploadSink != nil {
            autoUploadEligibleAssetIDs.insert(assetID)
            processUploadQueue()
        }

        notify()
    }

    /// 标记 asset 正在从相机下载。
    func markDownloading(assetID: String, filename: String) {
        guard !excludedAssetIDs.contains(assetID) else { return }
        if let index = tasks.firstIndex(where: { $0.assetID == assetID }) {
            tasks[index].status = .downloading
            tasks[index].errorMessage = nil
        } else {
            tasks.insert(
                CameraTransferTask(assetID: assetID, filename: filename, status: .downloading),
                at: 0
            )
        }
        notify()
    }

    /// 标记 asset 下载失败。
    func failDownload(assetID: String, message: String) {
        guard let index = tasks.firstIndex(where: { $0.assetID == assetID }) else { return }
        tasks[index].status = .failed
        tasks[index].errorMessage = message
        notify()
    }

    /// 并发上传边拍边传新照片；拍后传输任务只能由用户显式上传。
    private func processUploadQueue() {
        guard uploadSink != nil else { return }

        while activeUploadAssetIDs.count < maxConcurrentUploads,
              let task = tasks.first(where: {
                  $0.status == .downloaded
                      && !activeUploadAssetIDs.contains($0.assetID)
                      && autoUploadEligibleAssetIDs.contains($0.assetID)
              }) {
            startConcurrentUpload(assetID: task.assetID)
        }
    }

    private func startConcurrentUpload(assetID: String) {
        guard !activeUploadAssetIDs.contains(assetID) else { return }
        activeUploadAssetIDs.insert(assetID)
        Task { @MainActor in
            await self.uploadTask(assetID: assetID)
            self.activeUploadAssetIDs.remove(assetID)
            self.processUploadQueue()
        }
    }

    private func uploadAssetIfNeeded(assetID: String) async {
        if activeUploadAssetIDs.contains(assetID) { return }
        guard let index = tasks.firstIndex(where: { $0.assetID == assetID }) else { return }
        if tasks[index].status == .uploaded { return }

        activeUploadAssetIDs.insert(assetID)
        defer { activeUploadAssetIDs.remove(assetID) }

        guard let refreshedIndex = tasks.firstIndex(where: { $0.assetID == assetID }) else { return }
        if tasks[refreshedIndex].status == .downloaded || tasks[refreshedIndex].status == .failed {
            tasks[refreshedIndex].status = .downloaded
            tasks[refreshedIndex].errorMessage = nil
            await uploadTask(assetID: assetID)
        }
    }

    private func uploadTask(assetID: String) async {
        guard let index = tasks.firstIndex(where: { $0.assetID == assetID }),
              let sink = uploadSink,
              let localURL = tasks[index].localURL
        else { return }

        tasks[index].status = .uploading
        tasks[index].errorMessage = nil
        notify()

        let filename = tasks[index].filename
        let fileType = filename.lowercased().hasSuffix(".mp4") ? 1 : 2
        var attempt = 0
        while attempt < maxRetries {
            do {
                let remoteURL = try await sink.upload(
                    localURL: localURL,
                    fileName: filename,
                    fileType: fileType,
                    progress: { [weak self] progress in
                        Task { @MainActor in
                            guard let self,
                                  let taskIndex = self.tasks.firstIndex(where: { $0.assetID == assetID }) else { return }
                            let lastNotifiedProgress = self.lastNotifiedProgressByAssetID[assetID] ?? -1
                            guard progress == 100 || progress - lastNotifiedProgress >= 10 else { return }
                            self.lastNotifiedProgressByAssetID[assetID] = progress
                            self.tasks[taskIndex].progress = progress
                            self.notify(progress == 100 ? .immediate : .deferred)
                        }
                    }
                )
                guard let taskIndex = tasks.firstIndex(where: { $0.assetID == assetID }) else { return }
                tasks[taskIndex].status = .uploaded
                tasks[taskIndex].remoteURL = remoteURL
                tasks[taskIndex].progress = 100
                autoUploadEligibleAssetIDs.remove(assetID)
                lastNotifiedProgressByAssetID.removeValue(forKey: assetID)
                notify()
                return
            } catch {
                attempt += 1
                guard let taskIndex = tasks.firstIndex(where: { $0.assetID == assetID }) else { return }
                if attempt >= maxRetries {
                    tasks[taskIndex].status = .failed
                    tasks[taskIndex].errorMessage = error.localizedDescription
                    lastNotifiedProgressByAssetID.removeValue(forKey: assetID)
                    notify()
                } else {
                    let delay = UInt64(pow(2.0, Double(attempt)))
                    try? await Task.sleep(nanoseconds: delay * 1_000_000_000)
                }
            }
        }
    }

    private func notify(_ mode: WiredTransferNotifyMode = .immediate) {
        switch mode {
        case .immediate:
            pendingDeferredNotifyTask?.cancel()
            pendingDeferredNotifyTask = nil
            onTasksUpdated?(tasks)
        case .deferred:
            let elapsed = Date().timeIntervalSince(lastDeferredNotifyDate)
            if elapsed >= deferredNotifyInterval {
                lastDeferredNotifyDate = Date()
                onTasksUpdated?(tasks)
                return
            }
            guard pendingDeferredNotifyTask == nil else { return }
            let delay = UInt64((deferredNotifyInterval - elapsed) * 1_000_000_000)
            pendingDeferredNotifyTask = Task { @MainActor in
                try? await Task.sleep(nanoseconds: delay)
                guard !Task.isCancelled else { return }
                self.lastDeferredNotifyDate = Date()
                self.pendingDeferredNotifyTask = nil
                self.onTasksUpdated?(self.tasks)
            }
        }
    }
}

private enum WiredTransferNotifyMode {
    case immediate
    case deferred
}