//
//  HomeMoreFunctionsViewController.swift
//  suixinkan
//

import SnapKit
import UIKit

// MARK: - Diffable 标识

/// 全部功能页 section 标识，区分常用应用与更多功能网格。
private enum HomeMoreSection: Hashable {
    case commonApps
    case moreFunctions
}

/// 全部功能页 item 标识，以菜单 URI 作为唯一键。
private enum HomeMoreItem: Hashable {
    case menu(uri: String)
}

/// 首页全部功能页，支持常用应用增删和更多功能网格展示。
final class HomeMoreFunctionsViewController: UIViewController {

    private let viewModel = HomeViewModel()
    private let commonMenuStore = HomeCommonMenuStore()
    private var commonURIs: [String] = []

    private lazy var collectionView: UICollectionView = {
        let layout = makeCollectionLayout()
        let collection = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collection.backgroundColor = AppDesignUIKit.pageBackground
        collection.delegate = self
        collection.register(HomeMoreMenuItemCell.self, forCellWithReuseIdentifier: HomeMoreMenuItemCell.reuseID)
        collection.register(
            CollectionSectionHeaderView.self,
            forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
            withReuseIdentifier: CollectionSectionHeaderView.reuseID
        )
        return collection
    }()

    /// Diffable 数据源，驱动常用应用与更多功能两个网格 section。
    private var dataSource: UICollectionViewDiffableDataSource<HomeMoreSection, HomeMoreItem>!

    /// 视图加载完成后的 UI 初始化与数据绑定。
    override func viewDidLoad() {
        super.viewDidLoad()
        title = "全部功能"
        view.backgroundColor = AppDesignUIKit.pageBackground
        navigationItem.largeTitleDisplayMode = .never

        configureDataSource()
        view.addSubview(collectionView)
        collectionView.snp.makeConstraints { make in
            make.edges.equalToSuperview()
        }

        viewModel.onChange = { [weak self] in
            self?.applySnapshot()
        }
        rebuildMenus()

        appServices.permissionContext.onChange = { [weak self] in
            self?.rebuildMenus()
        }
    }

    /// 构建 Compositional Layout，两个 section 均为带标题的三列网格。
    private func makeCollectionLayout() -> UICollectionViewCompositionalLayout {
        UICollectionViewCompositionalLayout { [weak self] sectionIndex, _ in
            guard let self,
                  let section = self.dataSource?.snapshot().sectionIdentifiers[safe: sectionIndex]
            else {
                return CollectionDiffableLayout.gridSection(itemHeight: 112)
            }
            let gridInsets = NSDirectionalEdgeInsets(
                top: AppMetrics.Spacing.xxSmall,
                leading: AppMetrics.Spacing.mediumLarge,
                bottom: AppMetrics.Spacing.xxSmall,
                trailing: AppMetrics.Spacing.mediumLarge
            )
            let grid = CollectionDiffableLayout.gridSection(
                columns: 3,
                itemHeight: 112,
                interItemSpacing: 14,
                lineSpacing: AppMetrics.Spacing.mediumLarge,
                contentInsets: gridInsets
            )
            switch section {
            case .commonApps:
                return CollectionDiffableLayout.addHeader(to: grid, height: 36)
            case .moreFunctions:
                return CollectionDiffableLayout.addHeader(to: grid, height: 36)
            }
        }
    }

    /// 注册 Diffable 数据源与 Cell 配置闭包。
    private func configureDataSource() {
        dataSource = UICollectionViewDiffableDataSource<HomeMoreSection, HomeMoreItem>(
            collectionView: collectionView
        ) { [weak self] collectionView, indexPath, item in
            guard let self,
                  case .menu(let uri) = item,
                  let section = self.dataSource.snapshot().sectionIdentifiers[safe: indexPath.section]
            else { return UICollectionViewCell() }

            let cell = collectionView.dequeueReusableCell(
                withReuseIdentifier: HomeMoreMenuItemCell.reuseID,
                for: indexPath
            ) as! HomeMoreMenuItemCell

            let isCommon = section == .commonApps
            let items = isCommon ? self.commonItems : self.moreItems
            guard let menuItem = items.first(where: { $0.uri == uri }) else { return cell }

            cell.configure(item: menuItem, isCommon: isCommon) { [weak self] in
                self?.toggleCommon(menuItem, isCommon: isCommon)
            }
            return cell
        }

        dataSource.supplementaryViewProvider = { [weak self] collectionView, kind, indexPath in
            guard let self,
                  kind == UICollectionView.elementKindSectionHeader,
                  let section = self.dataSource.snapshot().sectionIdentifiers[safe: indexPath.section],
                  let header = collectionView.dequeueReusableSupplementaryView(
                      ofKind: kind,
                      withReuseIdentifier: CollectionSectionHeaderView.reuseID,
                      for: indexPath
                  ) as? CollectionSectionHeaderView
            else { return nil }
            let title = section == .commonApps ? "常用应用" : "更多功能"
            header.configure(title: title)
            return header
        }
    }

    /// 根据当前常用应用与权限菜单构建 snapshot 并应用 diff 更新。
    private func applySnapshot(animated: Bool = true) {
        var snapshot = NSDiffableDataSourceSnapshot<HomeMoreSection, HomeMoreItem>()

        snapshot.appendSections([.commonApps, .moreFunctions])
        snapshot.appendItems(
            commonItems.map { HomeMoreItem.menu(uri: $0.uri) },
            toSection: .commonApps
        )
        snapshot.appendItems(
            moreItems.map { HomeMoreItem.menu(uri: $0.uri) },
            toSection: .moreFunctions
        )

        dataSource.apply(snapshot, animatingDifferences: animated)
    }

    /// 按当前角色权限重建首页菜单与常用应用。
    private func rebuildMenus() {
        let services = appServices
        viewModel.buildMenus(
            from: services.permissionContext.rolePermissions,
            currentRoleId: services.permissionContext.currentRole?.id
        )
        commonURIs = commonMenuStore.load(menuItems: viewModel.menuItems)
        applySnapshot()
    }

    private var commonItems: [HomeMenuItem] {
        commonURIs.compactMap { menuItem(for: $0) }
    }

    private var moreItems: [HomeMenuItem] {
        viewModel.menuItems.filter { !isCommonURI($0.uri) }
    }

    /// 按 URI 解析并返回可用菜单项。
    private func menuItem(for uri: String) -> HomeMenuItem? {
        let availableURIs = Set(viewModel.menuItems.map(\.uri))
        let resolvedUri = HomeMenuRouter.canonicalURI(for: uri, availableURIs: availableURIs)
        guard let existing = viewModel.menuItems.first(where: { $0.uri == resolvedUri }) else { return nil }
        return HomeMenuItem(
            title: HomeMenuRouter.displayTitle(for: resolvedUri, fallback: existing.title),
            uri: resolvedUri,
            iconSrc: existing.iconSrc
        )
    }

    /// 判断 URI 是否已在常用应用中。
    private func isCommonURI(_ uri: String) -> Bool {
        let aliasKey = HomeMenuRouter.menuAliasKey(for: uri)
        return commonURIs.contains { HomeMenuRouter.menuAliasKey(for: $0) == aliasKey }
    }

    /// 切换菜单项的常用应用状态。
    private func toggleCommon(_ item: HomeMenuItem, isCommon: Bool) {
        if isCommon {
            commonURIs = commonMenuStore.remove(item.uri, current: commonURIs)
        } else {
            commonURIs = commonMenuStore.add(item.uri, current: commonURIs, menuItems: viewModel.menuItems)
        }
        applySnapshot()
    }

    /// 打开菜单对应页面。
    private func openMenu(_ item: HomeMenuItem) {
        let route = HomeMenuRouter.resolve(uri: item.uri, title: item.title)
        if case .destination(let homeRoute) = route, homeRoute == .moreFunctions { return }
        HomeMenuRouting.openRoute(route, from: self)
    }
}

// MARK: - UICollectionViewDelegate

extension HomeMoreFunctionsViewController: UICollectionViewDelegate {
    /// 点击网格项打开对应功能页（加减按钮由 Cell 内部处理）。
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard let item = dataSource.itemIdentifier(for: indexPath),
              case .menu(let uri) = item
        else { return }

        let allItems = commonItems + moreItems
        guard let menuItem = allItems.first(where: { $0.uri == uri }) else { return }
        openMenu(menuItem)
    }
}

// MARK: - Menu Item Cell

/// 全部功能页菜单网格单项 Cell，支持常用应用加减操作。
private final class HomeMoreMenuItemCell: UICollectionViewCell {
    static let reuseID = "HomeMoreMenuItemCell"

    private let iconView = UIImageView()
    private let titleLabel = UILabel()
    private let toggleButton = UIButton(type: .system)
    private var onToggle: (() -> Void)?

    /// 初始化实例。
    override init(frame: CGRect) {
        super.init(frame: frame)
        contentView.backgroundColor = .white
        contentView.layer.cornerRadius = 8

        titleLabel.font = .systemFont(ofSize: AppMetrics.FontSize.callout)
        titleLabel.textColor = UIColor(hex: 0x252525)
        titleLabel.textAlignment = .center
        titleLabel.numberOfLines = 1
        titleLabel.adjustsFontSizeToFitWidth = true

        toggleButton.addTarget(self, action: #selector(toggleTapped), for: .touchUpInside)
        contentView.addSubview(toggleButton)

        let stack = UIStackView(arrangedSubviews: [iconView, titleLabel])
        stack.axis = .vertical
        stack.spacing = AppMetrics.Spacing.mediumLarge + 1
        stack.alignment = .center
        contentView.addSubview(stack)

        stack.snp.makeConstraints { make in
            make.center.equalToSuperview()
            make.leading.trailing.equalToSuperview().inset(4)
        }
        iconView.snp.makeConstraints { make in
            make.width.height.equalTo(34)
        }
        toggleButton.snp.makeConstraints { make in
            make.top.trailing.equalToSuperview().inset(2)
            make.width.height.equalTo(28)
        }
        iconView.contentMode = .scaleAspectFit
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    /// 配置菜单项展示内容与常用应用切换按钮。
    func configure(item: HomeMenuItem, isCommon: Bool, onToggle: @escaping () -> Void) {
        self.onToggle = onToggle
        titleLabel.text = item.title
        let symbol = UIImage(systemName: HomeIconCatalog.iconName(for: item.uri))
        iconView.loadRemoteImage(urlString: item.iconSrc, contentMode: .scaleAspectFit, placeholder: symbol)
        iconView.tintColor = AppDesign.primary
        let iconName = isCommon ? "minus.circle.fill" : "plus.circle.fill"
        toggleButton.setImage(UIImage(systemName: iconName), for: .normal)
        toggleButton.tintColor = isCommon ? UIColor(hex: 0xFF1111) : AppDesignUIKit.primary
    }

    /// 点击加减按钮切换常用应用状态。
    @objc private func toggleTapped() {
        onToggle?()
    }
}

/// 安全下标，避免 section 越界。
private extension Array {
    subscript(safe index: Int) -> Element? {
        indices.contains(index) ? self[index] : nil
    }
}