//
//  CameraTransferPipeline.swift
//  suixinkan
//
//  Created by Codex on 2026/6/29.
//

import Foundation

/// 相机传输编排器，负责监听新照片、下载到本地并按需调用上传 Sink。
@MainActor
final class CameraTransferPipeline {
    var onTasksUpdated: (([CameraTransferTask]) -> Void)?

    private(set) var tasks: [CameraTransferTask] = []
    private let cameraService: any CameraServiceProtocol
    private var uploadSink: (any CameraAssetUploadSink)?
    private var uploadEnabled = true
    private var activeUploadAssetIDs: Set<String> = []
    private var pendingDeferredNotifyTask: Task<Void, Never>?
    private var lastDeferredNotifyDate = Date.distantPast
    private var lastNotifiedProgressByAssetID: [String: Int] = [:]
    private var inFlightAssetIDs: Set<String> = []
    private let maxRetries = 3
    private let deferredNotifyInterval: TimeInterval = 0.15
    private let maxConcurrentUploads = 3

    /// 初始化传输管道，并注入相机服务。
    init(cameraService: any CameraServiceProtocol) {
        self.cameraService = cameraService
        cameraService.onNewAsset = { [weak self] asset in
            Task { @MainActor in
                await self?.handleNewAsset(asset, skipIfExists: false)
            }
        }
    }

    /// 配置上传 Sink 与是否自动上传。
    func configure(uploadSink: (any CameraAssetUploadSink)?, uploadEnabled: Bool) {
        self.uploadSink = uploadSink
        self.uploadEnabled = uploadEnabled
    }

    /// 启动相机连接。
    func connect() async {
        await cameraService.connect()
    }

    /// 断开相机连接。
    func disconnect() async {
        await cameraService.disconnect()
    }

    /// 当前相机连接状态。
    var connectionState: CameraConnectionState {
        cameraService.connectionState
    }

    /// 设置连接状态变化回调。
    var onConnectionStateChange: ((CameraConnectionState) -> Void)? {
        get { nil }
        set {
            cameraService.onConnectionStateChange = newValue
        }
    }

    /// 重试所有失败的上传任务。
    func retryFailedUploads() async {
        guard uploadEnabled, uploadSink != nil else { return }
        for index in tasks.indices where tasks[index].status == .failed {
            tasks[index].status = .downloaded
            tasks[index].errorMessage = nil
        }
        notify()
        processUploadQueue()
    }

    /// 手动上传指定 asset 列表（拍完再传模式）。
    func uploadAssets(withIDs assetIDs: [String]) async {
        guard uploadSink != nil else { return }
        for assetID in assetIDs {
            if activeUploadAssetIDs.contains(assetID) { continue }
            guard let index = tasks.firstIndex(where: { $0.assetID == assetID }) else { continue }
            if tasks[index].status == .uploaded { continue }
            if tasks[index].localURL == nil {
                await downloadAsset(assetID: assetID)
            }
            guard let refreshedIndex = tasks.firstIndex(where: { $0.assetID == assetID }) else { continue }
            if tasks[refreshedIndex].status == .downloaded || tasks[refreshedIndex].status == .failed {
                tasks[refreshedIndex].status = .downloaded
                tasks[refreshedIndex].errorMessage = nil
                await uploadTask(assetID: assetID)
            }
        }
    }

    /// 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)
    }

    /// 同步相机内已有照片到任务列表（不自动上传）。
    func syncExistingPhotos() async {
        guard cameraService.connectionState.isConnected else { return }
        do {
            let assets = try await cameraService.listAssets()
            for asset in assets {
                await handleNewAsset(asset, skipIfExists: true)
            }
        } catch {
            CameraTetheringLogger.log("syncExistingPhotos 失败: \(error.localizedDescription)", logger: CameraTetheringLogger.transfer)
        }
    }

    /// 清空所有传输记录及本地文件。
    func clearAllTransfers() {
        for task in tasks {
            guard let localURL = task.localURL,
                  FileManager.default.fileExists(atPath: localURL.path)
            else { continue }
            try? FileManager.default.removeItem(at: localURL)
        }
        tasks.removeAll()
        notify()
    }

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

    private func handleNewAsset(_ asset: CameraAsset, skipIfExists: Bool) async {
        if skipIfExists,
           let existing = tasks.first(where: { $0.assetID == asset.id }),
           existing.status == .uploaded || existing.status == .downloaded {
            return
        }
        if inFlightAssetIDs.contains(asset.id) { return }
        if tasks.contains(where: { $0.assetID == asset.id && $0.status == .downloading }) { return }

        inFlightAssetIDs.insert(asset.id)
        defer { inFlightAssetIDs.remove(asset.id) }

        let assetID = asset.id
        if let existingIndex = tasks.firstIndex(where: { $0.assetID == assetID }) {
            tasks[existingIndex].status = .downloading
            tasks[existingIndex].errorMessage = nil
        } else {
            let task = CameraTransferTask(
                assetID: asset.id,
                filename: asset.filename,
                capturedAt: CameraTransferTask.capturedAtString(from: asset.creationDate),
                status: .downloading
            )
            tasks.insert(task, at: 0)
        }
        notify()

        await downloadAsset(assetID: assetID, asset: asset)

        if uploadEnabled,
           uploadSink != nil,
           tasks.first(where: { $0.assetID == assetID })?.status == .downloaded {
            processUploadQueue()
        }
    }

    /// 下载指定 asset 到本地；始终按 assetID 定位任务，避免连拍时 index 失效。
    private func downloadAsset(assetID: String, asset: CameraAsset? = nil) async {
        guard tasks.contains(where: { $0.assetID == assetID }) else { return }

        do {
            let resolvedAsset: CameraAsset
            if let asset {
                resolvedAsset = asset
            } else if let cached = try? await cameraService.listAssets().first(where: { $0.id == assetID }) {
                resolvedAsset = cached
            } else {
                throw CameraServiceError.assetNotFound
            }

            let localURL = try await cameraService.downloadAsset(resolvedAsset)
            let destination: URL

            if CameraDownloadStorage.isInDownloadsDirectory(localURL) {
                destination = localURL
            } else {
                destination = CameraDownloadStorage.uniqueLocalURL(for: resolvedAsset.filename)
                if FileManager.default.fileExists(atPath: destination.path) {
                    try FileManager.default.removeItem(at: destination)
                }
                try FileManager.default.moveItem(at: localURL, to: destination)
            }

            guard let index = tasks.firstIndex(where: { $0.assetID == assetID }) else { return }
            tasks[index].localPath = CameraDownloadStorage.relativePath(for: destination)
            if tasks[index].capturedAt?.isEmpty != false {
                tasks[index].capturedAt = CameraTransferTask.capturedAtString(from: resolvedAsset.creationDate)
            }
            tasks[index].status = .downloaded
            tasks[index].progress = 0
            notify()
        } catch {
            guard let index = tasks.firstIndex(where: { $0.assetID == assetID }) else { return }
            tasks[index].status = .failed
            tasks[index].errorMessage = error.localizedDescription
            notify()
        }
    }

    /// 并发上传已下载任务；边拍边传时限制并发数，避免网络与内存被打满。
    private func processUploadQueue() {
        guard uploadEnabled, uploadSink != nil else { return }

        while activeUploadAssetIDs.count < maxConcurrentUploads,
              let task = tasks.first(where: { $0.status == .downloaded && !activeUploadAssetIDs.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 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
                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: CameraTransferNotifyMode = .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 CameraTransferNotifyMode {
    case immediate
    case deferred
}