import Foundation
import Combine

/// 按日分组的相机照片区块。
struct CameraPhotoSection: Equatable, Identifiable {
    var id: String { dayKey }
    let dayKey: String
    let title: String
    let photos: [CameraObject]
}

/// 相机历史导入页状态机。
enum CameraImportState: Equatable {
    case idle
    case loading
    case loaded(sections: [CameraPhotoSection])
    case importing(current: Int, total: Int)
    case finished(importedCount: Int)
    case failed(message: String)
}

/// 相机 SD 卡历史照片多选导入 ViewModel。
@MainActor
final class CameraHistoryImportViewModel: ObservableObject {
    @Published private(set) var state: CameraImportState = .idle
    @Published private(set) var selectedPhotoIDs: Set<String> = []
    @Published private(set) var shouldShowSonyMTPHelp = false
    @Published private(set) var sections: [CameraPhotoSection] = []

    let albumId: Int
    let accountKey: String
    private weak var driver: (any CameraDriver)?
    private let photoSink: OTGPhotoSink
    private let onImported: () -> Void

    private var allPhotos: [CameraObject] = []
    private var existingAlbumPhotoIDs: Set<String> = []
    private var thumbnailCache: [String: Data] = [:]

    /// 初始化历史导入 ViewModel。
    init(
        albumId: Int,
        accountKey: String,
        driver: any CameraDriver,
        photoSink: OTGPhotoSink,
        onImported: @escaping () -> Void
    ) {
        self.albumId = albumId
        self.accountKey = accountKey
        self.driver = driver
        self.photoSink = photoSink
        self.onImported = onImported
    }

    /// 通过 Driver 拉取相机内照片并按日分组。
    func loadPhotos() {
        guard let driver else {
            state = .failed(message: "相机未连接")
            return
        }

        state = .loading

        Task {
            do {
                existingAlbumPhotoIDs = await photoSink.existingCameraObjectIDs()
                let objects = try await driver.listObjects()
                allPhotos = objects
                let sections = Self.groupByDay(objects)
                if sections.isEmpty {
                    self.sections = []
                    state = .failed(message: "相机中没有可导入的照片")
                } else {
                    self.sections = sections
                    state = .loaded(sections: sections)
                }
                updateSonyMTPHelpVisibility()
            } catch {
                state = .failed(message: error.localizedDescription)
                updateSonyMTPHelpVisibility()
            }
        }
    }

    /// 判断照片是否已在当前相册。
    func isPhotoAlreadyInAlbum(id: String) -> Bool {
        existingAlbumPhotoIDs.contains(id)
    }

    /// 切换单张照片选中状态。
    func togglePhoto(id: String) {
        guard !isPhotoAlreadyInAlbum(id: id) else { return }
        if selectedPhotoIDs.contains(id) {
            selectedPhotoIDs.remove(id)
        } else {
            selectedPhotoIDs.insert(id)
        }
    }

    /// 切换分组全选。
    func toggleSection(_ section: CameraPhotoSection) {
        let importableIDs = Set(section.photos.filter { !isPhotoAlreadyInAlbum(id: $0.id) }.map(\.id))
        guard !importableIDs.isEmpty else { return }
        if importableIDs.isSubset(of: selectedPhotoIDs) {
            selectedPhotoIDs.subtract(importableIDs)
        } else {
            selectedPhotoIDs.formUnion(importableIDs)
        }
    }

    func isPhotoSelected(id: String) -> Bool {
        selectedPhotoIDs.contains(id)
    }

    func isSectionFullySelected(_ section: CameraPhotoSection) -> Bool {
        let ids = section.photos.filter { !isPhotoAlreadyInAlbum(id: $0.id) }.map(\.id)
        return !ids.isEmpty && ids.allSatisfy { selectedPhotoIDs.contains($0) }
    }

    func hasImportablePhotos(in section: CameraPhotoSection) -> Bool {
        section.photos.contains { !isPhotoAlreadyInAlbum(id: $0.id) }
    }

    /// 加载相机缩略图。
    func thumbnailData(for photo: CameraObject, maxPixelSize: Int) async -> Data? {
        if let cached = thumbnailCache[photo.id] {
            return cached
        }
        guard let driver else { return nil }
        guard let data = await driver.requestThumbnailData(for: photo, maxPixelSize: maxPixelSize) else {
            return nil
        }
        thumbnailCache[photo.id] = data
        return data
    }

    /// 顺序下载选中项并写入本地存储。
    func importSelected() {
        guard let driver else { return }
        let selected = allPhotos.filter {
            selectedPhotoIDs.contains($0.id) && !isPhotoAlreadyInAlbum(id: $0.id)
        }
        guard !selected.isEmpty else { return }

        state = .importing(current: 0, total: selected.count)

        Task {
            let tempDir = FileManager.default.temporaryDirectory
                .appendingPathComponent("camera-history-import", isDirectory: true)
            try? FileManager.default.createDirectory(at: tempDir, withIntermediateDirectories: true)
            var imported = 0

            for (index, object) in selected.enumerated() {
                do {
                    let downloadedURL = try await driver.downloadObject(object, to: tempDir)
                    _ = try await photoSink.saveDownloadedFile(
                        at: downloadedURL,
                        filename: object.filename,
                        capturedAt: object.capturedAt,
                        cameraObjectID: object.id
                    )
                    imported += 1
                    state = .importing(current: index + 1, total: selected.count)
                } catch {
                    OTGLog.error(.connection, "import failed: \(object.filename) \(error.localizedDescription)")
                }
            }

            selectedPhotoIDs.removeAll()
            state = .finished(importedCount: imported)
            onImported()
        }
    }

    private func updateSonyMTPHelpVisibility() {
        guard driver?.platform == .sony else {
            shouldShowSonyMTPHelp = false
            return
        }
        switch state {
        case .loaded(let sections):
            shouldShowSonyMTPHelp = sections.isEmpty
        case .failed:
            shouldShowSonyMTPHelp = allPhotos.isEmpty
        default:
            shouldShowSonyMTPHelp = false
        }
    }

    private static func groupByDay(_ photos: [CameraObject]) -> [CameraPhotoSection] {
        let calendar = Calendar.current
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "zh_CN")
        formatter.dateFormat = "yyyy年M月d日"

        let grouped = Dictionary(grouping: photos) { photo in
            calendar.startOfDay(for: photo.capturedAt)
        }

        return grouped.keys
            .sorted(by: >)
            .map { day in
                let items = grouped[day]!.sorted { $0.capturedAt > $1.capturedAt }
                let dayKey = dayKeyString(for: day, calendar: calendar)
                let title = sectionTitle(for: day, formatter: formatter, calendar: calendar)
                return CameraPhotoSection(dayKey: dayKey, title: title, photos: items)
            }
    }

    private static func dayKeyString(for day: Date, calendar: Calendar) -> String {
        let components = calendar.dateComponents([.year, .month, .day], from: day)
        return String(format: "%04d-%02d-%02d", components.year ?? 0, components.month ?? 0, components.day ?? 0)
    }

    private static func sectionTitle(for day: Date, formatter: DateFormatter, calendar: Calendar) -> String {
        if calendar.isDateInToday(day) { return "今天" }
        if calendar.isDateInYesterday(day) { return "昨天" }
        return formatter.string(from: day)
    }
}