//
//  StatisticsViewController.swift
//  suixinkan
//

import SnapKit
import UIKit

// MARK: - Diffable 标识

/// 统计页 section 标识，区分空状态、周期切换、汇总与每日明细。
private enum StatisticsSection: Hashable {
    case empty
    case period
    case summary
    case daily
}

/// 统计页 item 标识，携带展示数据以保证 diff 后 Cell 内容同步更新。
private enum StatisticsItem: Hashable {
    case emptyContext
    case period(StatisticsPeriod)
    case summary(StatisticsSummaryResponse)
    case dailyEmpty
    case daily(StatisticsDailyItem)
}

/// 数据 Tab 根页面，展示订单统计汇总和每日明细。
final class StatisticsViewController: UIViewController {

    private let viewModel = StatisticsViewModel()

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

    private lazy var refreshControl = UIRefreshControl()

    /// Diffable 数据源，驱动多 section 列表与分页插入动画。
    private var dataSource: UICollectionViewDiffableDataSource<StatisticsSection, StatisticsItem>!

    /// 视图加载完成后的 UI 初始化与数据绑定。
    override func viewDidLoad() {
        super.viewDidLoad()
        title = "数据"
        view.backgroundColor = AppDesignUIKit.pageBackground
        configureDataSource()
        view.addSubview(collectionView)
        collectionView.snp.makeConstraints { make in make.edges.equalToSuperview() }
        refreshControl.addTarget(self, action: #selector(refreshPulled), for: .valueChanged)
        collectionView.refreshControl = refreshControl

        viewModel.onChange = { [weak self] in self?.applySnapshot() }
        appServices.accountContext.onChange = { [weak self] in Task { await self?.reload(showLoading: true) } }
        appServices.permissionContext.onChange = { [weak self] in Task { await self?.reload(showLoading: true) } }
        applySnapshot(animated: false)
        Task { await reload(showLoading: true) }
    }

    /// 构建 Compositional Layout，按 section 类型分配全宽卡片布局。
    private func makeCollectionLayout() -> UICollectionViewCompositionalLayout {
        UICollectionViewCompositionalLayout { [weak self] sectionIndex, _ in
            guard let self else { return CollectionDiffableLayout.fullWidthSection() }
            let snapshot = self.dataSource?.snapshot()
            let section = snapshot?.sectionIdentifiers[safe: sectionIndex]
            switch section {
            case .empty:
                return CollectionDiffableLayout.fullWidthSection(estimatedHeight: 360)
            case .period:
                return CollectionDiffableLayout.fullWidthSection(estimatedHeight: 56)
            case .summary:
                return CollectionDiffableLayout.fullWidthSection(estimatedHeight: 280)
            case .daily:
                return CollectionDiffableLayout.addHeader(
                    to: CollectionDiffableLayout.fullWidthSection(estimatedHeight: 52),
                    height: 36
                )
            case .none:
                return CollectionDiffableLayout.fullWidthSection()
            }
        }
    }

    /// 注册 Diffable 数据源与 Cell 配置闭包。
    private func configureDataSource() {
        dataSource = UICollectionViewDiffableDataSource<StatisticsSection, StatisticsItem>(
            collectionView: collectionView
        ) { [weak self] collectionView, indexPath, item in
            guard let self else { return UICollectionViewCell() }
            switch item {
            case .emptyContext:
                let cell = collectionView.dequeueReusableCell(
                    withReuseIdentifier: StatisticsEmptyCell.reuseID,
                    for: indexPath
                ) as! StatisticsEmptyCell
                let empty = self.makeEmptyStateView(
                    title: "缺少经营上下文",
                    message: "请先在首页选择景区后查看数据看板。",
                    systemImage: "chart.bar.doc.horizontal"
                )
                cell.setHostedView(empty, height: 360)
                return cell
            case .period(let selectedPeriod):
                let cell = collectionView.dequeueReusableCell(
                    withReuseIdentifier: StatisticsPeriodCell.reuseID,
                    for: indexPath
                ) as! StatisticsPeriodCell
                cell.configure(selectedPeriod: selectedPeriod) { [weak self] period in
                    self?.selectPeriod(period)
                }
                return cell
            case .summary(let summary):
                let cell = collectionView.dequeueReusableCell(
                    withReuseIdentifier: StatisticsSummaryCell.reuseID,
                    for: indexPath
                ) as! StatisticsSummaryCell
                cell.configure(
                    periodText: self.viewModel.selectedPeriod.selectedTimeText,
                    summary: summary,
                    amountText: self.amountText
                )
                return cell
            case .dailyEmpty:
                let cell = collectionView.dequeueReusableCell(
                    withReuseIdentifier: StatisticsEmptyCell.reuseID,
                    for: indexPath
                ) as! StatisticsEmptyCell
                cell.configurePlainText("暂无数据", height: 52)
                return cell
            case .daily(let dailyItem):
                let cell = collectionView.dequeueReusableCell(
                    withReuseIdentifier: StatisticsDailyCell.reuseID,
                    for: indexPath
                ) as! StatisticsDailyCell
                cell.configure(item: dailyItem, amountText: self.amountText)
                return cell
            }
        }

        dataSource.supplementaryViewProvider = { collectionView, kind, indexPath in
            guard kind == UICollectionView.elementKindSectionHeader,
                  let section = self.dataSource.snapshot().sectionIdentifiers[safe: indexPath.section],
                  section == .daily,
                  let header = collectionView.dequeueReusableSupplementaryView(
                      ofKind: kind,
                      withReuseIdentifier: CollectionSectionHeaderView.reuseID,
                      for: indexPath
                  ) as? CollectionSectionHeaderView
            else { return nil }
            header.configure(title: "每日明细")
            return header
        }
    }

    /// 根据 ViewModel 状态构建 snapshot 并应用 diff 更新。
    private func applySnapshot(animated: Bool = true) {
        var snapshot = NSDiffableDataSourceSnapshot<StatisticsSection, StatisticsItem>()

        if currentScenicId == nil {
            snapshot.appendSections([.empty])
            snapshot.appendItems([.emptyContext], toSection: .empty)
        } else {
            snapshot.appendSections([.period, .summary, .daily])
            snapshot.appendItems([.period(viewModel.selectedPeriod)], toSection: .period)
            snapshot.appendItems([.summary(viewModel.summary)], toSection: .summary)

            if viewModel.loading, viewModel.dailyItems.isEmpty {
                // 首次加载中不展示占位行，避免闪烁。
            } else if viewModel.dailyItems.isEmpty {
                snapshot.appendItems([.dailyEmpty], toSection: .daily)
            } else {
                let items = viewModel.dailyItems.map { StatisticsItem.daily($0) }
                snapshot.appendItems(items, toSection: .daily)
            }
        }

        dataSource.apply(snapshot, animatingDifferences: animated)
    }

    /// 下拉刷新触发。
    @objc private func refreshPulled() {
        Task {
            await reload(showLoading: false)
            refreshControl.endRefreshing()
        }
    }

    private var currentScenicId: Int? { appServices.accountContext.currentScenic?.id }
    private var currentRoleId: Int? { appServices.permissionContext.currentRole?.id }

    /// 重新加载汇总与第一页日数据。
    private func reload(showLoading: Bool) async {
        guard currentScenicId != nil else {
            applySnapshot()
            return
        }
        do {
            try await appServices.globalLoading.withOptionalLoading(showLoading, message: "加载数据...") {
                try await self.viewModel.reload(
                    api: self.appServices.statisticsAPI,
                    scenicId: self.currentScenicId,
                    roleId: self.currentRoleId,
                    showLoading: false
                )
            }
        } catch {
            showToast(error.localizedDescription)
        }
    }

    /// 切换统计周期并重新加载数据。
    private func selectPeriod(_ period: StatisticsPeriod) {
        Task {
            do {
                try await appServices.globalLoading.withLoading(message: "加载数据...") {
                    try await viewModel.selectPeriod(
                        period,
                        api: appServices.statisticsAPI,
                        scenicId: currentScenicId,
                        roleId: currentRoleId
                    )
                }
            } catch {
                showToast(error.localizedDescription)
            }
        }
    }

    /// 加载每日明细下一页。
    private func loadMore() async {
        do {
            try await viewModel.loadMore(
                api: appServices.statisticsAPI,
                scenicId: currentScenicId,
                roleId: currentRoleId
            )
        } catch {
            showToast(error.localizedDescription)
        }
    }

    /// 格式化金额展示文本。
    private func amountText(_ value: Double) -> String {
        "¥\(String(format: "%.2f", value))"
    }
}

// MARK: - UICollectionViewDelegate

extension StatisticsViewController: UICollectionViewDelegate {
    /// 最后一项日明细即将展示时触发分页加载。
    func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
        guard let item = dataSource.itemIdentifier(for: indexPath),
              case .daily(let dailyItem) = item,
              dailyItem.date == viewModel.dailyItems.last?.date
        else { return }
        Task { await loadMore() }
    }
}

// MARK: - Cells

/// 统计周期切换 Cell，横向展示快捷时间段按钮。
private final class StatisticsPeriodCell: UICollectionViewCell {
    static let reuseID = "StatisticsPeriodCell"
    private var onSelect: ((StatisticsPeriod) -> Void)?
    private let stack = UIStackView()

    /// 初始化实例。
    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .clear
        stack.axis = .horizontal
        stack.spacing = 8
        stack.distribution = .fillEqually
        contentView.addSubview(stack)
        stack.snp.makeConstraints { make in make.edges.equalToSuperview().inset(12) }
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError() }

    /// 配置展示内容。
    func configure(selectedPeriod: StatisticsPeriod, onSelect: @escaping (StatisticsPeriod) -> Void) {
        self.onSelect = onSelect
        stack.arrangedSubviews.forEach { $0.removeFromSuperview() }
        for period in StatisticsPeriod.allCases {
            let button = UIButton(type: .system)
            button.setTitle(period.rawValue, for: .normal)
            button.titleLabel?.font = .systemFont(ofSize: AppMetrics.FontSize.subheadline, weight: period == selectedPeriod ? .semibold : .regular)
            button.setTitleColor(period == selectedPeriod ? AppDesignUIKit.primary : AppDesignUIKit.textSecondary, for: .normal)
            button.backgroundColor = period == selectedPeriod ? AppDesignUIKit.primarySoft : UIColor(hex: 0xF4F4F4)
            button.layer.cornerRadius = 6
            button.tag = StatisticsPeriod.allCases.firstIndex(of: period) ?? 0
            button.addTarget(self, action: #selector(periodTapped(_:)), for: .touchUpInside)
            stack.addArrangedSubview(button)
        }
    }

    /// 点击周期按钮后回调选中项。
    @objc private func periodTapped(_ sender: UIButton) {
        let period = StatisticsPeriod.allCases[sender.tag]
        onSelect?(period)
    }
}

/// 统计汇总 Cell，展示订单金额、数量、客单价等指标卡片。
private final class StatisticsSummaryCell: UICollectionViewCell {
    static let reuseID = "StatisticsSummaryCell"
    private let stack = UIStackView()

    /// 初始化实例。
    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .clear
        stack.axis = .vertical
        stack.spacing = 8
        contentView.addSubview(stack)
        stack.snp.makeConstraints { make in make.edges.equalToSuperview().inset(12) }
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError() }

    /// 配置展示内容。
    func configure(periodText: String, summary: StatisticsSummaryResponse, amountText: (Double) -> String) {
        stack.arrangedSubviews.forEach { $0.removeFromSuperview() }
        let dateLabel = UILabel()
        dateLabel.text = "已选日期：\(periodText)"
        dateLabel.font = .systemFont(ofSize: AppMetrics.FontSize.subheadline)
        stack.addArrangedSubview(dateLabel)

        stack.addArrangedSubview(summaryCard("订单总金额", amountText(summary.orderAmountValue), UIColor(hex: 0x22C55E)))
        let row = UIStackView()
        row.axis = .horizontal
        row.spacing = 8
        row.distribution = .fillEqually
        row.addArrangedSubview(summaryCard("订单总数", "\(summary.orderCount)单", UIColor(hex: 0x7F00FF)))
        row.addArrangedSubview(summaryCard("实收金额", amountText(summary.receivedAmountValue), UIColor(hex: 0x22C55E)))
        stack.addArrangedSubview(row)

        let row2 = UIStackView()
        row2.axis = .horizontal
        row2.spacing = 8
        row2.distribution = .fillEqually
        row2.addArrangedSubview(summaryCard("客单价", amountText(summary.orderPriceAverageValue), AppDesignUIKit.primary))
        row2.addArrangedSubview(summaryCard("退款金额", amountText(summary.refundAmountValue), UIColor(hex: 0xEF4444)))
        stack.addArrangedSubview(row2)
    }

    /// 创建统计摘要卡片视图。
    private func summaryCard(_ title: String, _ value: String, _ color: UIColor) -> UIView {
        let card = UIView()
        card.backgroundColor = color.withAlphaComponent(0.08)
        card.layer.cornerRadius = 8
        let titleLabel = UILabel()
        titleLabel.text = title
        titleLabel.font = .systemFont(ofSize: AppMetrics.FontSize.caption)
        let valueLabel = UILabel()
        valueLabel.text = value
        valueLabel.font = .systemFont(ofSize: AppMetrics.FontSize.title3, weight: .bold)
        valueLabel.textColor = color
        let inner = UIStackView(arrangedSubviews: [titleLabel, valueLabel])
        inner.axis = .vertical
        inner.spacing = 4
        card.addSubview(inner)
        inner.snp.makeConstraints { make in make.edges.equalToSuperview().inset(12) }
        card.snp.makeConstraints { make in make.height.greaterThanOrEqualTo(72) }
        return card
    }
}

/// 每日统计明细 Cell，展示日期、订单数与实收金额。
private final class StatisticsDailyCell: UICollectionViewCell {
    static let reuseID = "StatisticsDailyCell"

    private let titleLabel = UILabel()
    private let detailLabel = UILabel()

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

        titleLabel.font = .systemFont(ofSize: AppMetrics.FontSize.subheadline, weight: .semibold)
        detailLabel.font = .systemFont(ofSize: AppMetrics.FontSize.caption)
        detailLabel.textColor = AppDesignUIKit.textSecondary

        contentView.addSubview(titleLabel)
        contentView.addSubview(detailLabel)
        titleLabel.snp.makeConstraints { make in
            make.leading.trailing.equalToSuperview().inset(16)
            make.top.equalToSuperview().inset(12)
        }
        detailLabel.snp.makeConstraints { make in
            make.leading.trailing.equalTo(titleLabel)
            make.top.equalTo(titleLabel.snp.bottom).offset(4)
            make.bottom.equalToSuperview().inset(12)
        }
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError() }

    /// 配置展示内容。
    func configure(item: StatisticsDailyItem, amountText: (Double) -> String) {
        titleLabel.text = item.date
        detailLabel.text = "\(item.orderCount)单 · 实收 \(amountText(item.receivedValue))"
    }
}

/// 空状态 Cell，用于缺少景区上下文或日明细为空时的占位展示。
private final class StatisticsEmptyCell: UICollectionViewCell {
    static let reuseID = "StatisticsEmptyCell"

    private var heightConstraint: Constraint?

    /// 初始化实例。
    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .clear
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError() }

    /// 嵌入外部构建的空状态视图并固定高度。
    func setHostedView(_ view: UIView, height: CGFloat) {
        contentView.subviews.forEach { $0.removeFromSuperview() }
        heightConstraint?.deactivate()
        contentView.addSubview(view)
        view.snp.makeConstraints { make in
            make.edges.equalToSuperview()
            heightConstraint = make.height.equalTo(height).constraint
        }
    }

    /// 配置纯文案占位，用于日明细为空场景。
    func configurePlainText(_ title: String, height: CGFloat) {
        contentView.subviews.forEach { $0.removeFromSuperview() }
        heightConstraint?.deactivate()
        let label = UILabel()
        label.text = title
        label.font = .systemFont(ofSize: AppMetrics.FontSize.subheadline)
        label.textColor = AppDesignUIKit.textSecondary
        label.textAlignment = .center
        contentView.addSubview(label)
        label.snp.makeConstraints { make in
            make.edges.equalToSuperview().inset(16)
            heightConstraint = make.height.equalTo(height).constraint
        }
    }
}

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