PDF_Office/PDF Office/PDF Master/Class/PDFWindowController/Toolbar/KMToolbarView.swift

//
//  KMToolbarView.swift
//  PDF Reader Pro
//
//  Created by tangchao on 2023/10/24.
//

import Cocoa

private let KMToolbarSpaceItemWidth = 30.0
private let KMToolbarLineItemWidth = 1.0
private let KMToolbarItemSpace = 8.0

@objc protocol KMToolbarViewDelegate: NSObjectProtocol {
    @objc optional func toolbar(_ toolbar: KMToolbarView, itemFor identifier: String) -> KMToolbarItemView
    
    @objc optional func toolbarAllowedItemIdentifiers(_ toolbar: KMToolbarView) -> [String]
    @objc optional func toolbarDefaultItemIdentifiers(_ toolbar: KMToolbarView) -> [String]
    
    @objc optional func toolbarLeftDefaultItemIdentifiers(_ toolbar: KMToolbarView) -> [String]
    @objc optional func toolbarRightDefaultItemIdentifiers(_ toolbar: KMToolbarView) -> [String]
}

@objcMembers class KMToolbarView: NSView {
    private var _toolbarIdentifier: String?
    var toolbarIdentifier: String? {
        get {
            return self._toolbarIdentifier
        }
    }
    
    private var _items: [KMToolbarItemView] = []
    var items: [KMToolbarItemView] {
        get {
            return self._items
        }
    }
    
    weak var delegate: KMToolbarViewDelegate?
    
    private var _visibleItems: [KMToolbarItemView] = []
    private var _invisibleItems: [KMToolbarItemView] = []
    private var _contentView: NSView?
    var contentView: NSView {
        get {
            if (self._contentView == nil) {
                self._contentView = NSView()
            }
            
            return self._contentView!
        }
    }
    lazy var moreButton: NSButton = {
        let _moreButton = NSButton()
        _moreButton.bezelStyle = .regularSquare
        _moreButton.isBordered = false
        _moreButton.font = .systemFont(ofSize: 20)
        _moreButton.title = " »"
        _moreButton.isHidden = true
        _moreButton.target = self
        _moreButton.action = #selector(_moreButtonAction)
        _moreButton.wantsLayer = true
        _moreButton.layer?.backgroundColor = NSColor.clear.cgColor
        return _moreButton
    }()
    
    var contentInset: NSEdgeInsets = NSEdgeInsetsZero
    
    private lazy var centerView: NSView = {
        let view = NSView()
        return view
    }()
    private lazy var leftView: NSView = {
        let view = NSView()
        return view
    }()
    
    private lazy var rightView: NSView = {
        let view = NSView()
        return view
    }()
    
    static let kLeftMargin: CGFloat = 8
    static let kHSpace: CGFloat = 8
    static let kRightMargin: CGFloat = 8
    static let kMoreWidth: CGFloat = 30
    
    private var _leftWidth: CGFloat = 0
    private var _centerWidth: CGFloat = 0
    private var _rightWidth: CGFloat = 0
    
    var allowsUserCustomization = false
    private var configWindowC_: KMToolbarConfigWindowController?
    
    deinit {
        KMPrint("KMToolbarView deinit")
    }
    
    convenience init(identifier: String) {
        self.init()
        
        self._toolbarIdentifier = identifier
        self._addTrackingArea()
    }
    
    override func menu(for event: NSEvent) -> NSMenu? {
        if self.allowsUserCustomization == false {
            return super.menu(for: event)
        }
        
        let menu = NSMenu()
        let item = NSMenuItem(title: NSLocalizedString("Customize Toolbar", comment: ""), action: #selector(_customToolbarItemAction), keyEquivalent: "")
        menu.addItem(item)
        return menu
    }
    
    // MARK: - Private Methods

    @objc private func _customToolbarItemAction(_ sender: NSMenuItem?) {
        if self.configWindowC_ == nil {
            self.configWindowC_ = KMToolbarConfigWindowController()
        }
        var leftCellIdentifiers = self.delegate?.toolbarLeftDefaultItemIdentifiers?(self) ?? []
        if leftCellIdentifiers.contains(KMDocumentHomeToolbarItemIdentifier) {
            leftCellIdentifiers.removeObject(KMDocumentHomeToolbarItemIdentifier)
        }
        self.configWindowC_?.leftCellIdentifiers = leftCellIdentifiers
        self.configWindowC_?.centerCellIdentifiers = (self.delegate?.toolbarDefaultItemIdentifiers?(self) ?? [])
        self.configWindowC_?.rightCellIdentifiers = (self.delegate?.toolbarRightDefaultItemIdentifiers?(self) ?? [])
        
        self.configWindowC_?.defaultCellIdentifiers = self.delegate?.toolbarAllowedItemIdentifiers?(self) ?? []
        self.window?.beginSheet((self.configWindowC_?.window)!, completionHandler: { [weak self] resp in
            self?.configWindowC_ = nil
            
            if resp == .OK {
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.3) {
                    KMDataManager.default.toolbarConfigDataUpdated = true
                    self?.reloadData()
                    KMDataManager.default.toolbarConfigDataUpdated = false
                }
            }
        })
    }
    
    private func _addTrackingArea() {
        let trackingArea = NSTrackingArea(rect: self.bounds, options: [.inVisibleRect, .activeInKeyWindow, .mouseMoved], owner: self)
        self.addTrackingArea(trackingArea)
    }
    
    @objc private func _moreButtonAction() {
        let menu = NSMenu()
        for item in self._invisibleItems {
            if (item.itemIdentifier == KMToolbarDividerItemIdentifier) {
                menu.addItem(NSMenuItem.separator())
            } else if (item.menuFormRepresentation != nil) {
                menu.addItem(item.menuFormRepresentation!)
            }
        }
        menu.popUp(positioning: menu.items.first, at: NSMakePoint(NSMaxX(self.moreButton.frame), NSMaxY(self.moreButton.frame)-5), in: self)
    }
    
    private func _updateMainView(_ left: Bool = true, _ right: Bool = true) {
        if (self.centerView.superview == nil) {
            self.addSubview(self.centerView)
        }

        if left {
            self._updateLeftView()
        }
        if right {
            self._updateRightView()
        }
        
        if(self.contentView.superview == nil) {
            self.centerView.addSubview(self.contentView)
        }
        
        for item in self.items {
            item.removeFromSuperview()
        }
        self._items = []
        
        var items: [KMToolbarItemView] = []
        let itemIdentifiers = self.delegate?.toolbarDefaultItemIdentifiers?(self) ?? []
        var lastItem: KMToolbarItemView?
        var iWidth: CGFloat = 0
        // -self._invisibleItems.count
        for i in 0 ..< (itemIdentifiers.count) {
            let itemIdentifier = itemIdentifiers[i]
            var item: KMToolbarItemView?
            if itemIdentifier == KMToolbarDividerItemIdentifier {
                item = KMToolbarCustomItemView(itemIdentifier: itemIdentifier, postition: .imageOnly, withPopMenu: nil)
            } else if itemIdentifier == KMNewToolbarSpaceItemIdentifier {
                item = KMToolbarCustomItemView(itemIdentifier: itemIdentifier, postition: .imageOnly, withPopMenu: nil)
                item?.layer?.backgroundColor = .clear
                item?.imageViewBox.borderColor = .clear
                item?.layer?.cornerRadius = 0.0
            } else if let data = self.delegate?.toolbar?(self, itemFor: itemIdentifier) {
                item = data
            }
            guard let data = item else {
                continue
            }

            self.contentView.addSubview(data)
            items.append(data)
            iWidth += data.itemWidth
            if lastItem != nil {
                // + 前一个的间距
                iWidth += Self.kHSpace
            }

            lastItem = item
        }
        self._items = items
        self._centerWidth = iWidth
        
        self.addSubview(self.moreButton)
    }
    
    // UI 20 16
    // item w 28 h 24
    private func _updateView(_ left: Bool = true, _ right: Bool = true) {
        if left {
            self._updateLeftView()
        }
        if right {
            self._updateRightView()
        }
        
        if(self.contentView.superview == nil) {
            self.addSubview(self.contentView)
        }
        
        for item in self.items {
            item.removeFromSuperview()
        }
        self._items = []
        
        var items: [KMToolbarItemView] = []
        let itemIdentifiers = self.delegate?.toolbarDefaultItemIdentifiers?(self) ?? []
        
        var lastItem: KMToolbarItemView?
        // -self._invisibleItems.count
        var iWidth: CGFloat = 0
        for i in 0 ..< itemIdentifiers.count {
            let itemIdentifier = itemIdentifiers[i]
            var item: KMToolbarItemView?
            if itemIdentifier == KMToolbarDividerItemIdentifier {
                item = KMToolbarCustomItemView(itemIdentifier: itemIdentifier, postition: .imageOnly, withPopMenu: nil)
            } else if itemIdentifier == KMNewToolbarSpaceItemIdentifier {
                item = KMToolbarCustomItemView(itemIdentifier: itemIdentifier, postition: .imageOnly, withPopMenu: nil)
                item?.layer?.backgroundColor = .clear
                item?.imageViewBox.borderColor = .clear
                item?.layer?.cornerRadius = 0.0
            } else if let data = self.delegate?.toolbar?(self, itemFor: itemIdentifier) {
                item = data
            }
            guard let data = item else {
                continue
            }

            self.contentView.addSubview(data)
            items.append(data)

            iWidth += data.itemWidth
            if lastItem != nil {
                // + 前一个的间距
                iWidth += Self.kHSpace
            }

            lastItem = item
        }
        self._items = items
        self._centerWidth = iWidth
        
        self.addSubview(self.moreButton)
    }
    
    private func _updateLeftView() {
        // 刷新前移除视图
        for item in self.leftView.subviews {
            item.removeFromSuperview()
        }
        if (self.leftView.superview != nil) {
            self.leftView.removeFromSuperview()
        }
        
        var iWidth: CGFloat = 0
        if let itemIdentifiers = self.delegate?.toolbarLeftDefaultItemIdentifiers?(self), itemIdentifiers.count > 0 {
            if (self.leftView.superview == nil) {
                self.addSubview(self.leftView)
            }
            self.leftView.mas_remakeConstraints { make in
                make?.left.equalTo()(self.mas_left)?.offset()(0)
                make?.top.equalTo()(self.mas_top)?.offset()(0)
                make?.bottom.equalTo()(self.mas_bottom)?.offset()(0)
            }
            
            var lastItem: KMToolbarItemView?
            for i in 0 ..< itemIdentifiers.count {
                let itemIdentifier = itemIdentifiers[i]
                var item: KMToolbarItemView?
                if itemIdentifier == KMToolbarDividerItemIdentifier {
                    item = KMToolbarCustomItemView(itemIdentifier: itemIdentifier, postition: .imageOnly, withPopMenu: nil)
                } else if itemIdentifier == KMNewToolbarSpaceItemIdentifier {
                    item = KMToolbarCustomItemView(itemIdentifier: itemIdentifier, postition: .imageOnly, withPopMenu: nil)
                    item?.layer?.backgroundColor = .clear
                    item?.imageViewBox.borderColor = .clear
                    item?.layer?.cornerRadius = 0.0
                } else if let data = self.delegate?.toolbar?(self, itemFor: itemIdentifier) {
                    item = data
                }
                guard let data = item else {
                    continue
                }
                
                self.leftView.addSubview(data)
                iWidth += data.itemWidth
                if lastItem != nil {
                    // + 前一个的间距
                    iWidth += Self.kHSpace
                }

                lastItem = item
            }
            
            iWidth += (Self.kLeftMargin + Self.kHSpace)
        }
        self._leftWidth = iWidth
    }
    
    private func _updateRightView() {
        // 刷新前移除视图
        for item in self.rightView.subviews {
            item.removeFromSuperview()
        }
        if (self.rightView.superview != nil) {
            self.rightView.removeFromSuperview()
        }
        
        var iWidth: CGFloat = 0
        if let itemIdentifiers = self.delegate?.toolbarRightDefaultItemIdentifiers?(self), itemIdentifiers.isEmpty == false {
            if (self.rightView.superview == nil) {
                self.addSubview(self.rightView)
            }
            
            var lastItem: KMToolbarItemView?
            for i in 0 ..< itemIdentifiers.count {
                let itemIdentifier = itemIdentifiers[i]
                
                var item: KMToolbarItemView?
                if itemIdentifier == KMToolbarDividerItemIdentifier {
                    item = KMToolbarCustomItemView(itemIdentifier: itemIdentifier, postition: .imageOnly, withPopMenu: nil)
                } else if itemIdentifier == KMNewToolbarSpaceItemIdentifier {
                    item = KMToolbarCustomItemView(itemIdentifier: itemIdentifier, postition: .imageOnly, withPopMenu: nil)
                    item?.layer?.backgroundColor = .clear
                    item?.imageViewBox.borderColor = .clear
                    item?.layer?.cornerRadius = 0.0;
                } else if let data = self.delegate?.toolbar?(self, itemFor: itemIdentifier) {
                    item = data
                }
                
                guard let data = item else {
                    continue
                }
                
                self.rightView.addSubview(data)
                iWidth += data.itemWidth
                if lastItem != nil {
                    // + 前一个的间距
                    iWidth += Self.kHSpace
                }

                lastItem = item
            }
            
            iWidth += Self.kRightMargin
        }
        self._rightWidth = iWidth
    }
    
    override func updateLayer() {
        super.updateLayer()
        
        if KMAppearance.isDarkMode() {
            self.layer?.backgroundColor = KMAppearance.Layout.l0Color().cgColor
        } else {
            self.layer?.backgroundColor = .clear
        }
        
        for item in self._items {
            item.interfaceThemeDidChanged(self.window?.appearance?.name ?? .aqua)
            item.customizeView?.interfaceThemeDidChanged(self.appearance?.name ?? .aqua)
        }
    }
    
    // MARK: - View Methods
    
    override func viewWillMove(toWindow newWindow: NSWindow?) {
        super.viewWillMove(toWindow: newWindow)
        
        if (newWindow != nil && self._contentView == nil) {
            let leftitemIdentifiers = self.delegate?.toolbarLeftDefaultItemIdentifiers?(self) ?? []
            if (leftitemIdentifiers.count > 0) {
                self._updateMainView()
            }else {
                self._updateView()
            }

            self.resizeSubviews(withOldSize: self.frame.size)
    
            let topLine = NSBox(frame: NSMakeRect(0, 0, self.frame.size.width, 0.5))
            topLine.boxType = .separator
            topLine.fillColor = .black
            self.addSubview(topLine)
            topLine.mas_makeConstraints { make in
                make?.left.right().equalTo()(self)
                make?.bottom.equalTo()(self.mas_bottom)?.offset()(-0.5)
                make?.height.offset()(0.5)
            }

            let bottomLine = NSBox(frame: NSMakeRect(0, 0, self.frame.size.width, 0.5))
            bottomLine.boxType = .separator
            bottomLine.fillColor = .black
            self.addSubview(bottomLine)
            bottomLine.mas_makeConstraints { make in
                make?.left.right().equalTo()(self)
                make?.top.equalTo()(self.mas_top)?.offset()(0.1)
                make?.height.offset()(0.5)
            }
        }

        if (newWindow != nil) {
            self._addTrackingArea()
        }
    }
    
    private func _layoutSubViewsIfNeed() {
        if (self._contentView == nil) {
            return
        }
        let moreButtonWidth = 18.0

        let leftW = self._leftWidth
        let contentW = self._centerWidth
        let rightW = self._rightWidth
//        KMPrint("width: \(leftW), \(contentW), \(rightW)")
//        KMPrint("\(self.frame.size.width)")
        
        let width = NSWidth(self.bounds) - self.contentInset.left - self.contentInset.right
        let height = NSHeight(self.bounds)
        let leftMargin = Self.kLeftMargin
        let hSpace = Self.kHSpace
        let itemH: CGFloat = 40
        var itemY: CGFloat = (height-itemH)*0.5
        let contentLength = leftW + contentW + rightW
        if (contentLength <= 0) {
            return
        }
        self._invisibleItems.removeAll()
        if width >= contentLength { // 左 + 中 + 右 显示(全)
            self.moreButton.isHidden = true
            let offset = width - contentLength
            self.leftView.frame = NSMakeRect(0, 0, leftW, height)
            var itemX: CGFloat = leftMargin
            for sv in self.leftView.subviews {
                guard let item = sv as? KMToolbarItemView else {
                    continue
                }
                item.isHidden = false
                itemY = (height-item.itemHeight)*0.5
                item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                itemX += item.itemWidth + hSpace
            }
            
            if self.isMain() {
                self.centerView.frame = NSMakeRect(leftW, 0, contentW + offset, height)
                self.contentView.frame = NSMakeRect(offset*0.5, 0, contentW, height)
            } else {
                self.contentView.frame = NSMakeRect(offset*0.5, 0, contentW, height)
            }
            itemX = 0
            for sv in self.contentView.subviews {
                guard let item = sv as? KMToolbarItemView else {
                    continue
                }
                item.isHidden = false
                itemY = (height-item.itemHeight)*0.5
                item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                itemX += item.itemWidth + hSpace
            }
            
            self.rightView.frame = NSMakeRect(leftW+contentW+offset, 0, rightW, height)
            itemX = 0
            for sv in self.rightView.subviews {
                guard let item = sv as? KMToolbarItemView else {
                    continue
                }
                item.isHidden = false
                itemY = (height-item.itemHeight)*0.5
                item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                itemX += item.itemWidth + hSpace
            }
            
            return
        } else { // 显示更多
            self.moreButton.isHidden = false
            self.moreButton.mas_remakeConstraints { make in
                make?.top.bottom().equalTo()(0)
                make?.width.mas_equalTo()(moreButtonWidth)
                make?.right.mas_equalTo()(-self.contentInset.right)
            }
            if width >= leftW + contentW { // 左 + 中 显示(全) 右显示不全
                let offset = width - leftW - contentW
                self.leftView.frame = NSMakeRect(0, 0, leftW, height)
                var itemX: CGFloat = leftMargin
                for sv in self.leftView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    item.isHidden = false
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                }
                
                if self.isMain() {
                    self.centerView.frame = NSMakeRect(leftW, 0, contentW, height)
                    self.contentView.frame = NSMakeRect(0, 0, contentW + offset, height)
                } else {
                    self.contentView.frame = NSMakeRect(leftW, 0, contentW, height)
                }
                itemX = 0
                for sv in self.contentView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    item.isHidden = false
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                }
                
                self.rightView.frame = NSMakeRect(leftW+contentW, 0, offset, height)
                itemX = 0
                for sv in self.rightView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                    let itemMinX = NSMinX(self.rightView.frame) + itemX
                    if itemMinX <= width {
                        item.isHidden = false
                    } else {
                        item.isHidden = true
                        self._invisibleItems.append(item)
                    }
                }
                
                return
            } else if width >= leftW { // 左 显示(全) 中 显示不全 右不显示
                let offset = width - leftW
                self.leftView.frame = NSMakeRect(0, 0, leftW, height)
                var itemX: CGFloat = leftMargin
                for sv in self.leftView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                    item.isHidden = false
                }
                
                if self.isMain() {
                    self.centerView.frame = NSMakeRect(leftW, 0, offset, height)
                    self.contentView.frame = NSMakeRect(0, 0,  offset, height)
                } else {
                    self.contentView.frame = NSMakeRect(leftW, 0, offset, height)
                }
                itemX = 0
                for sv in self.contentView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                    let itemMinX = leftW + itemX
                    if itemMinX <= width {
                        item.isHidden = false
                    } else {
                        item.isHidden = true
                        self._invisibleItems.append(item)
                    }
                }
                
                self.rightView.frame = NSMakeRect(leftW+contentW, 0, 0, height)
                itemX = 0
                for sv in self.rightView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                    item.isHidden = true
                    self._invisibleItems.append(item)
                }
                return
            } else { // 左显示不全 中 + 右 不显示
                let offset = width - leftW
                self.leftView.frame = NSMakeRect(0, 0, offset, height)
                var itemX: CGFloat = leftMargin
                for sv in self.leftView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                    if itemX <= width {
                        item.isHidden = false
                    } else {
                        item.isHidden = true
                        self._invisibleItems.append(item)
                    }
                }
                
                if self.isMain() {
                    self.centerView.frame = NSMakeRect(leftW, 0, 0, height)
                    self.contentView.frame = NSMakeRect(0, 0, 0, height)
                } else {
                    self.contentView.frame = NSMakeRect(leftW, 0, 0, height)
                }
                itemX = 0
                for sv in self.contentView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                    item.isHidden = true
                    self._invisibleItems.append(item)
                }
                
                self.rightView.frame = NSMakeRect(leftW+contentW, 0, 0, height)
                itemX = 0
                for sv in self.rightView.subviews {
                    guard let item = sv as? KMToolbarItemView else {
                        continue
                    }
                    itemY = (height-item.itemHeight)*0.5
                    item.frame = NSMakeRect(itemX, itemY, item.itemWidth, item.itemHeight)
                    itemX += item.itemWidth + hSpace
                    item.isHidden = true
                    self._invisibleItems.append(item)
                }
                return
            }
        }
    }
    
    func hasLeft() -> Bool {
        if let items = self.delegate?.toolbarLeftDefaultItemIdentifiers?(self) {
            return items.count > 0
        }
        return false
    }
    func hasRight() -> Bool {
        if let items = self.delegate?.toolbarRightDefaultItemIdentifiers?(self) {
            return items.count > 0
        }
        return false
    }
    func hasCenter() -> Bool {
        if let items = self.delegate?.toolbarDefaultItemIdentifiers?(self) {
            return items.count > 0
        }
        return false
    }
    func isMain() -> Bool {
        if self.contentView.superview == self {
            return false
        }
        return true
    }
    
    override func resizeSubviews(withOldSize oldSize: NSSize) {
        super.resizeSubviews(withOldSize: oldSize)
        
        self._layoutSubViewsIfNeed()
    }
    
    func reloadData() {
        let leftitemIdentifiers = self.delegate?.toolbarLeftDefaultItemIdentifiers?(self) ?? []
        if (leftitemIdentifiers.count > 0) {
            self._updateMainView()
        } else {
            self._updateView()
        }
        
        self.resizeSubviews(withOldSize: self.frame.size)
    }
    
    func itemForItemIdentifier(_ itemIdentifier: String) -> KMToolbarItemView? {
        for item in self.items {
            if (item.itemIdentifier == itemIdentifier) {
                return item
            }
        }
        return nil
    }
}