//
//  TravelAlbumAIRetouchTemplateViewController.swift
//  suixinkan
//

import Kingfisher
import SnapKit
import UIKit

/// AI 修图模板选择 Sheet，按工作流展示所需横向模板列表与固定底部操作。
final class TravelAlbumAIRetouchTemplateViewController: BaseViewController {
    /// 页面使用的 collection section。
    private enum Section: Hashable {
        case templates(TravelAlbumAIRetouchTemplateCategory)
        case mode
    }

    /// 页面使用的 diffable item。
    private enum Item: Hashable {
        case template(TravelAlbumAIRetouchTemplateCategory, TravelAlbumAIRetouchTemplate)
        case mode
    }

    private let viewModel: TravelAlbumAIRetouchTemplateViewModel
    private let api: any TravelAlbumServing
    private let onSubmitted: () -> Void

    private let titleLabel = UILabel()
    private lazy var collectionView = UICollectionView(frame: .zero, collectionViewLayout: makeLayout())
    private var dataSource: UICollectionViewDiffableDataSource<Section, Item>!
    private let statusContainer = UIView()
    private let statusIndicator = UIActivityIndicatorView(style: .medium)
    private let statusLabel = UILabel()
    private let retryButton = UIButton(type: .system)
    private let bottomBar = UIView()
    private let bottomDivider = UIView()
    private let footerStack = UIStackView()
    private let validationLabel = UILabel()
    private let actionStack = UIStackView()
    private let cancelButton = UIButton(type: .system)
    private let confirmButton = UIButton(type: .system)

    /// 创建 AI 修图模板选择 Sheet。
    init(
        viewModel: TravelAlbumAIRetouchTemplateViewModel,
        api: any TravelAlbumServing,
        onSubmitted: @escaping () -> Void
    ) {
        self.viewModel = viewModel
        self.api = api
        self.onSubmitted = onSubmitted
        super.init(nibName: nil, bundle: nil)
        modalPresentationStyle = .pageSheet
        configureSheetPresentation()
    }

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

    override func setupUI() {
        view.backgroundColor = AIRetouchTemplateStyle.pageBackground
        view.accessibilityIdentifier = "travelAlbum.aiRetouchTemplateSheet"

        titleLabel.text = "AI修图"
        titleLabel.textColor = AIRetouchTemplateStyle.textPrimary
        titleLabel.font = .systemFont(ofSize: 20, weight: .semibold)
        titleLabel.textAlignment = .center
        titleLabel.accessibilityTraits = .header

        collectionView.backgroundColor = .clear
        collectionView.showsVerticalScrollIndicator = false
        collectionView.alwaysBounceVertical = true
        collectionView.delegate = self
        collectionView.accessibilityIdentifier = "travelAlbum.aiRetouchTemplateCollection"
        collectionView.register(
            TravelAlbumAIRetouchTemplateCell.self,
            forCellWithReuseIdentifier: TravelAlbumAIRetouchTemplateCell.reuseIdentifier
        )
        collectionView.register(
            TravelAlbumAIRetouchModeCell.self,
            forCellWithReuseIdentifier: TravelAlbumAIRetouchModeCell.reuseIdentifier
        )
        collectionView.register(
            TravelAlbumAIRetouchSectionHeader.self,
            forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
            withReuseIdentifier: TravelAlbumAIRetouchSectionHeader.reuseIdentifier
        )
        configureDataSource()

        statusLabel.textColor = AIRetouchTemplateStyle.textSecondary
        statusLabel.font = .systemFont(ofSize: 14)
        statusLabel.textAlignment = .center
        statusLabel.numberOfLines = 0
        retryButton.setTitle("重试", for: .normal)
        retryButton.titleLabel?.font = .systemFont(ofSize: 15, weight: .semibold)
        retryButton.accessibilityIdentifier = "travelAlbum.aiRetouchRetryButton"

        bottomBar.backgroundColor = .white
        bottomBar.accessibilityIdentifier = "travelAlbum.aiRetouchBottomBar"
        bottomDivider.backgroundColor = AIRetouchTemplateStyle.border
        validationLabel.textColor = AIRetouchTemplateStyle.danger
        validationLabel.font = .systemFont(ofSize: 12, weight: .medium)
        validationLabel.textAlignment = .center
        validationLabel.numberOfLines = 0
        validationLabel.accessibilityIdentifier = "travelAlbum.aiRetouchValidationLabel"

        footerStack.axis = .vertical
        footerStack.spacing = 8
        footerStack.alignment = .fill
        actionStack.axis = .horizontal
        actionStack.spacing = 12
        actionStack.distribution = .fillEqually
        actionStack.alignment = .fill
        configureCancelButton()
        configureConfirmButton()
        actionStack.addArrangedSubview(cancelButton)
        actionStack.addArrangedSubview(confirmButton)
        footerStack.addArrangedSubview(validationLabel)
        footerStack.addArrangedSubview(actionStack)

        view.addSubview(titleLabel)
        view.addSubview(collectionView)
        view.addSubview(statusContainer)
        statusContainer.addSubview(statusIndicator)
        statusContainer.addSubview(statusLabel)
        statusContainer.addSubview(retryButton)
        view.addSubview(bottomBar)
        bottomBar.addSubview(bottomDivider)
        bottomBar.addSubview(footerStack)
    }

    override func setupConstraints() {
        titleLabel.snp.makeConstraints { make in
            make.top.equalTo(view.safeAreaLayoutGuide).offset(12)
            make.leading.trailing.equalToSuperview().inset(18)
            make.height.equalTo(30)
        }
        bottomBar.snp.makeConstraints { make in
            make.leading.trailing.bottom.equalToSuperview()
        }
        bottomDivider.snp.makeConstraints { make in
            make.top.leading.trailing.equalToSuperview()
            make.height.equalTo(0.5)
        }
        footerStack.snp.makeConstraints { make in
            make.top.equalToSuperview().offset(10)
            make.leading.trailing.equalToSuperview().inset(18)
            make.bottom.equalTo(view.safeAreaLayoutGuide).offset(-12)
        }
        actionStack.snp.makeConstraints { make in
            make.height.equalTo(48)
        }
        collectionView.snp.makeConstraints { make in
            make.top.equalTo(titleLabel.snp.bottom).offset(8)
            make.leading.trailing.equalToSuperview()
            make.bottom.equalTo(bottomBar.snp.top)
        }
        statusContainer.snp.makeConstraints { make in
            make.edges.equalTo(collectionView)
        }
        statusIndicator.snp.makeConstraints { make in
            make.centerX.equalToSuperview()
            make.centerY.equalToSuperview().offset(-32)
        }
        statusLabel.snp.makeConstraints { make in
            make.top.equalTo(statusIndicator.snp.bottom).offset(14)
            make.leading.trailing.equalToSuperview().inset(40)
        }
        retryButton.snp.makeConstraints { make in
            make.top.equalTo(statusLabel.snp.bottom).offset(12)
            make.centerX.equalToSuperview()
            make.height.equalTo(36)
            make.bottom.lessThanOrEqualToSuperview()
        }
    }

    override func bindActions() {
        cancelButton.addTarget(self, action: #selector(cancelTapped), for: .touchUpInside)
        confirmButton.addTarget(self, action: #selector(confirmTapped), for: .touchUpInside)
        retryButton.addTarget(self, action: #selector(retryTapped), for: .touchUpInside)
        viewModel.onStateChange = { [weak self] in
            Task { @MainActor in self?.applyViewModel() }
        }
        viewModel.onShowMessage = { [weak self] message in
            Task { @MainActor in self?.showToast(message) }
        }
        viewModel.onSubmitted = { [weak self] in
            Task { @MainActor in
                guard let self else { return }
                self.dismiss(animated: true, completion: self.onSubmitted)
            }
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        applyViewModel()
        Task { await viewModel.loadTemplates(api: api) }
    }

    private func configureSheetPresentation() {
        guard let sheet = sheetPresentationController else { return }
        sheet.detents = [.large()]
        sheet.selectedDetentIdentifier = .large
        sheet.prefersGrabberVisible = true
        sheet.prefersScrollingExpandsWhenScrolledToEdge = false
    }

    private func configureCancelButton() {
        var configuration = UIButton.Configuration.filled()
        configuration.title = "取消"
        configuration.baseBackgroundColor = .white
        configuration.baseForegroundColor = AIRetouchTemplateStyle.primary
        configuration.background.cornerRadius = 14
        configuration.background.strokeColor = AIRetouchTemplateStyle.primary.withAlphaComponent(0.55)
        configuration.background.strokeWidth = 1
        configuration.titleTextAttributesTransformer = buttonTitleTransformer
        cancelButton.configuration = configuration
        cancelButton.accessibilityIdentifier = "travelAlbum.aiRetouchCancelButton"
    }

    private func configureConfirmButton() {
        var configuration = UIButton.Configuration.filled()
        configuration.title = "确定"
        configuration.baseBackgroundColor = AIRetouchTemplateStyle.primary
        configuration.baseForegroundColor = .white
        configuration.background.cornerRadius = 14
        configuration.titleTextAttributesTransformer = buttonTitleTransformer
        confirmButton.configuration = configuration
        confirmButton.accessibilityIdentifier = "travelAlbum.aiRetouchConfirmButton"
    }

    private var buttonTitleTransformer: UIConfigurationTextAttributesTransformer {
        UIConfigurationTextAttributesTransformer { attributes in
            var attributes = attributes
            attributes.font = .systemFont(ofSize: 16, weight: .semibold)
            return attributes
        }
    }

    private func configureDataSource() {
        dataSource = UICollectionViewDiffableDataSource<Section, Item>(collectionView: collectionView) {
            [weak self] collectionView, indexPath, item in
            guard let self else { return nil }
            switch item {
            case .template(let category, let template):
                let cell = collectionView.dequeueReusableCell(
                    withReuseIdentifier: TravelAlbumAIRetouchTemplateCell.reuseIdentifier,
                    for: indexPath
                ) as! TravelAlbumAIRetouchTemplateCell
                cell.apply(
                    template: template,
                    selected: self.viewModel.selectedTemplateId(for: category) == template.id
                )
                return cell
            case .mode:
                let cell = collectionView.dequeueReusableCell(
                    withReuseIdentifier: TravelAlbumAIRetouchModeCell.reuseIdentifier,
                    for: indexPath
                ) as! TravelAlbumAIRetouchModeCell
                cell.apply()
                return cell
            }
        }
        dataSource.supplementaryViewProvider = { [weak self] collectionView, kind, indexPath in
            guard kind == UICollectionView.elementKindSectionHeader,
                  let self,
                  self.dataSource.snapshot().sectionIdentifiers.indices.contains(indexPath.section),
                  case .templates(let category) = self.dataSource.snapshot().sectionIdentifiers[indexPath.section] else {
                return nil
            }
            let header = collectionView.dequeueReusableSupplementaryView(
                ofKind: kind,
                withReuseIdentifier: TravelAlbumAIRetouchSectionHeader.reuseIdentifier,
                for: indexPath
            ) as! TravelAlbumAIRetouchSectionHeader
            header.apply(title: category.title, optional: self.viewModel.isOptional(category))
            return header
        }
    }

    private func makeLayout() -> UICollectionViewCompositionalLayout {
        UICollectionViewCompositionalLayout { [weak self] sectionIndex, _ in
            guard let self,
                  self.dataSource != nil,
                  self.dataSource.snapshot().sectionIdentifiers.indices.contains(sectionIndex) else {
                return nil
            }
            switch self.dataSource.snapshot().sectionIdentifiers[sectionIndex] {
            case .templates:
                let itemSize = NSCollectionLayoutSize(
                    widthDimension: .absolute(118),
                    heightDimension: .absolute(154)
                )
                let item = NSCollectionLayoutItem(layoutSize: itemSize)
                let group = NSCollectionLayoutGroup.horizontal(layoutSize: itemSize, subitems: [item])
                let section = NSCollectionLayoutSection(group: group)
                section.orthogonalScrollingBehavior = .continuousGroupLeadingBoundary
                section.interGroupSpacing = 12
                section.contentInsets = NSDirectionalEdgeInsets(top: 4, leading: 18, bottom: 12, trailing: 18)
                section.boundarySupplementaryItems = [
                    NSCollectionLayoutBoundarySupplementaryItem(
                        layoutSize: NSCollectionLayoutSize(
                            widthDimension: .fractionalWidth(1),
                            heightDimension: .absolute(40)
                        ),
                        elementKind: UICollectionView.elementKindSectionHeader,
                        alignment: .top
                    ),
                ]
                return section
            case .mode:
                let itemSize = NSCollectionLayoutSize(
                    widthDimension: .fractionalWidth(1),
                    heightDimension: .absolute(72)
                )
                let item = NSCollectionLayoutItem(layoutSize: itemSize)
                let group = NSCollectionLayoutGroup.horizontal(layoutSize: itemSize, subitems: [item])
                let section = NSCollectionLayoutSection(group: group)
                section.contentInsets = NSDirectionalEdgeInsets(top: 12, leading: 18, bottom: 22, trailing: 18)
                return section
            }
        }
    }

    @MainActor
    private func applyViewModel() {
        let isLoadFailure = viewModel.loadErrorMessage != nil
        statusContainer.isHidden = !viewModel.isLoading && !isLoadFailure
        collectionView.isHidden = viewModel.isLoading || isLoadFailure
        if viewModel.isLoading {
            statusIndicator.startAnimating()
            statusLabel.text = "正在加载修图模板…"
            retryButton.isHidden = true
        } else if let message = viewModel.loadErrorMessage {
            statusIndicator.stopAnimating()
            statusLabel.text = message
            retryButton.isHidden = false
        } else {
            statusIndicator.stopAnimating()
            statusLabel.text = nil
            retryButton.isHidden = true
        }

        validationLabel.text = viewModel.validationMessage
        validationLabel.isHidden = viewModel.validationMessage == nil
        cancelButton.isEnabled = !viewModel.isSubmitting
        confirmButton.isEnabled = viewModel.canSubmit
        confirmButton.alpha = viewModel.canSubmit ? 1 : 0.45
        var confirmConfiguration = confirmButton.configuration
        confirmConfiguration?.title = viewModel.isSubmitting ? "提交中" : "确定"
        confirmConfiguration?.showsActivityIndicator = viewModel.isSubmitting
        confirmButton.configuration = confirmConfiguration
        isModalInPresentation = viewModel.isSubmitting
        applySnapshot()
    }

    private func applySnapshot() {
        var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
        for category in viewModel.visibleCategories {
            appendTemplates(category, to: &snapshot)
        }
        snapshot.appendSections([.mode])
        snapshot.appendItems([.mode], toSection: .mode)
        snapshot.reconfigureItems(snapshot.itemIdentifiers)
        dataSource.apply(snapshot, animatingDifferences: true)
    }

    private func appendTemplates(
        _ category: TravelAlbumAIRetouchTemplateCategory,
        to snapshot: inout NSDiffableDataSourceSnapshot<Section, Item>
    ) {
        let section = Section.templates(category)
        snapshot.appendSections([section])
        snapshot.appendItems(
            viewModel.templates(for: category).map { Item.template(category, $0) },
            toSection: section
        )
    }

    @objc private func cancelTapped() {
        guard !viewModel.isSubmitting else { return }
        dismiss(animated: true)
    }

    @objc private func confirmTapped() {
        guard viewModel.canSubmit else {
            if let message = viewModel.validationMessage { showToast(message) }
            return
        }
        Task { await viewModel.submit(api: api) }
    }

    @objc private func retryTapped() {
        Task { await viewModel.loadTemplates(api: api) }
    }
}

extension TravelAlbumAIRetouchTemplateViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        guard let item = dataSource.itemIdentifier(for: indexPath),
              case .template(let category, let template) = item else { return }
        viewModel.toggleTemplate(id: template.id, category: category)
    }
}

/// AI 修图模板卡片，展示模板预览、名称和明确选中态。
final class TravelAlbumAIRetouchTemplateCell: UICollectionViewCell {
    static let reuseIdentifier = "TravelAlbumAIRetouchTemplateCell"

    private let previewImageView = UIImageView()
    private let nameLabel = UILabel()
    private let checkView = UIImageView()

    override init(frame: CGRect) {
        super.init(frame: frame)
        contentView.backgroundColor = .white
        contentView.layer.cornerRadius = 12
        contentView.layer.borderWidth = 1
        contentView.clipsToBounds = true

        previewImageView.contentMode = .scaleAspectFill
        previewImageView.clipsToBounds = true
        previewImageView.backgroundColor = UIColor(hex: 0xEDF2F8)
        nameLabel.font = .systemFont(ofSize: 13, weight: .medium)
        nameLabel.textColor = AIRetouchTemplateStyle.textPrimary
        nameLabel.textAlignment = .center
        nameLabel.lineBreakMode = .byTruncatingTail
        checkView.image = UIImage(systemName: "checkmark.circle.fill")
        checkView.tintColor = AIRetouchTemplateStyle.primary
        checkView.backgroundColor = .white
        checkView.layer.cornerRadius = 10

        contentView.addSubview(previewImageView)
        contentView.addSubview(nameLabel)
        contentView.addSubview(checkView)
        previewImageView.snp.makeConstraints { make in
            make.top.leading.trailing.equalToSuperview()
            make.height.equalTo(116)
        }
        nameLabel.snp.makeConstraints { make in
            make.top.equalTo(previewImageView.snp.bottom)
            make.leading.trailing.equalToSuperview().inset(6)
            make.bottom.equalToSuperview()
        }
        checkView.snp.makeConstraints { make in
            make.top.trailing.equalToSuperview().inset(8)
            make.size.equalTo(20)
        }
    }

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

    override func prepareForReuse() {
        super.prepareForReuse()
        previewImageView.kf.cancelDownloadTask()
        previewImageView.image = nil
    }

    /// 更新模板内容与选中状态。
    func apply(template: TravelAlbumAIRetouchTemplate, selected: Bool) {
        nameLabel.text = template.name
        if let url = URL(string: template.previewURL), !template.previewURL.isEmpty {
            previewImageView.contentMode = .scaleAspectFill
            previewImageView.kf.setImage(
                with: url,
                placeholder: UIImage(systemName: "photo")?.withTintColor(
                    AIRetouchTemplateStyle.textSecondary,
                    renderingMode: .alwaysOriginal
                )
            )
        } else {
            previewImageView.image = UIImage(systemName: "photo")
            previewImageView.tintColor = AIRetouchTemplateStyle.textSecondary
            previewImageView.contentMode = .scaleAspectFit
        }
        contentView.layer.borderColor = (
            selected ? AIRetouchTemplateStyle.primary : AIRetouchTemplateStyle.border
        ).cgColor
        contentView.layer.borderWidth = selected ? 2 : 1
        checkView.isHidden = !selected
        isSelected = selected
        accessibilityLabel = template.name
        accessibilityValue = selected ? "已选择" : "未选择"
        accessibilityTraits = selected ? [.button, .selected] : [.button]
    }
}

/// AI 修图模板分组标题，可附带“选填”标签。
final class TravelAlbumAIRetouchSectionHeader: UICollectionReusableView {
    static let reuseIdentifier = "TravelAlbumAIRetouchSectionHeader"

    private let titleLabel = UILabel()
    private let optionalLabel = UILabel()

    override init(frame: CGRect) {
        super.init(frame: frame)
        titleLabel.font = .systemFont(ofSize: 17, weight: .semibold)
        titleLabel.textColor = AIRetouchTemplateStyle.textPrimary
        optionalLabel.text = "选填"
        optionalLabel.font = .systemFont(ofSize: 11, weight: .medium)
        optionalLabel.textColor = AIRetouchTemplateStyle.primary
        optionalLabel.textAlignment = .center
        optionalLabel.backgroundColor = AIRetouchTemplateStyle.primary.withAlphaComponent(0.1)
        optionalLabel.layer.cornerRadius = 8
        optionalLabel.clipsToBounds = true

        addSubview(titleLabel)
        addSubview(optionalLabel)
        titleLabel.snp.makeConstraints { make in
            make.leading.equalToSuperview().offset(18)
            make.centerY.equalToSuperview()
        }
        optionalLabel.snp.makeConstraints { make in
            make.leading.equalTo(titleLabel.snp.trailing).offset(8)
            make.centerY.equalTo(titleLabel)
            make.width.equalTo(38)
            make.height.equalTo(20)
            make.trailing.lessThanOrEqualToSuperview().offset(-18)
        }
    }

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

    /// 更新分组标题与选填标签。
    func apply(title: String, optional: Bool) {
        titleLabel.text = title
        optionalLabel.isHidden = !optional
        accessibilityLabel = optional ? "\(title)，选填" : title
        accessibilityTraits = .header
    }
}

/// AI 修图模式卡片，展示计费方式与剩余张数占位。
final class TravelAlbumAIRetouchModeCell: UICollectionViewCell {
    static let reuseIdentifier = "TravelAlbumAIRetouchModeCell"

    private let titleLabel = UILabel()
    private let remainingLabel = UILabel()

    override init(frame: CGRect) {
        super.init(frame: frame)
        contentView.backgroundColor = .white
        contentView.layer.cornerRadius = 14
        contentView.layer.borderWidth = 1
        contentView.layer.borderColor = AIRetouchTemplateStyle.border.cgColor

        titleLabel.font = .systemFont(ofSize: 15, weight: .semibold)
        titleLabel.textColor = AIRetouchTemplateStyle.textPrimary
        remainingLabel.font = .monospacedDigitSystemFont(ofSize: 14, weight: .medium)
        remainingLabel.textColor = AIRetouchTemplateStyle.primary
        remainingLabel.textAlignment = .right

        contentView.addSubview(titleLabel)
        contentView.addSubview(remainingLabel)
        titleLabel.snp.makeConstraints { make in
            make.leading.equalToSuperview().offset(16)
            make.centerY.equalToSuperview()
        }
        remainingLabel.snp.makeConstraints { make in
            make.trailing.equalToSuperview().offset(-16)
            make.centerY.equalToSuperview()
            make.leading.greaterThanOrEqualTo(titleLabel.snp.trailing).offset(12)
        }
    }

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

    /// 应用当前固定修图模式与额度占位文案。
    func apply() {
        titleLabel.text = "AI精修  按张收费"
        remainingLabel.text = "剩余--张"
        accessibilityIdentifier = "travelAlbum.aiRetouchModeCell"
        accessibilityLabel = "AI精修，按张收费，剩余张数暂不可用"
    }
}

/// AI 修图模板页视觉常量。
private enum AIRetouchTemplateStyle {
    static let primary = UIColor(hex: 0x1677FF)
    static let pageBackground = UIColor(hex: 0xF7F9FC)
    static let textPrimary = UIColor(hex: 0x172033)
    static let textSecondary = UIColor(hex: 0x7F8A9E)
    static let border = UIColor(hex: 0xDCE4EF)
    static let danger = UIColor(hex: 0xE53935)
}