Conversion function

Description.txt

Исходные данные:
Коллекция с уникальными элементами (содержат id).
Элементы иммутабельны.
Функция преобразования:
  Принимает новую коллекцию и делает замещение с дельтой.
    Дельта состоит из операций: добавления, замещения, удаления.
  Хранит последнюю дельту.
  Нотифицирует делегат с данными дельты.
  
Функция восстановления:
  Принимает последнюю дельту и восстанавливает исходную коллекцию.

Example.swift

import UIKit

protocol CollectionDelegate {
    func onCollectionChanged(diff:[[String: Any]])
    func onDiffApply(dict:[String: Any])
}

enum OperationType {
    case removed
    case replaced
    case added
}

class MyCollection: NSObject {
    private var dict: [String: Any] = [:]
    private var lastDiff: [[String: Any]] = []
    public var delegate: CollectionDelegate?
    
    open func replace(newDict: [String: Any]) -> Void {
        
        lastDiff = []
        
        dict.forEach { (key: String, value: Any) in
            
            if newDict[key] == nil {
                lastDiff.append(["newValue": [key:value], "operation": OperationType.removed])
            }
            
        }
        
        newDict.forEach { (key: String, value: Any) in
            
            if let elem = dict[key] {
                lastDiff.append(["newValue": [key:value], "operation": OperationType.replaced, "oldValue": elem])
            } else {
                lastDiff.append(["newValue": [key:value], "operation": OperationType.added])
            }
            
        }
        
        dict = newDict
        
        if delegate != nil {
            delegate?.onCollectionChanged(diff: lastDiff)
        }
    }
    
    open func applyDiff(diff: [[String:Any]]) {
        
        for elem in diff {
            if let operation: OperationType = elem["operation"] as? OperationType,
                let newValue:[String: Any] = elem["newValue"] as? [String: Any] {
                switch operation {
                case .added:
                    if let key = newValue.keys.first {
                        dict.removeValue(forKey: key)
                    }
                case .replaced:
                    if let oldValue:[String: Any] = elem["oldValue"] as? [String: Any],
                        let key = oldValue.keys.first {
                        dict[key] = oldValue.values.first
                    }
                case .removed:
                    if let key = newValue.keys.first {
                        dict[key] = newValue.values.first
                    }
                }
                
            }
        }
        
        if delegate != nil {
            delegate?.onDiffApply(dict: dict)
        }
    }
    
    open func applyLast() {
        if !lastDiff.isEmpty {
            applyDiff(diff: lastDiff)
            lastDiff = []
        }
    }
}

class DelegateCollect: NSObject, CollectionDelegate {
    func onCollectionChanged(diff: [[String: Any]]) {
        print("\(diff)\n")
    }
    
    func onDiffApply(dict: [String : Any]) {
        print("\(dict)\n")
    }
}

var collect: MyCollection = MyCollection()
var delegate: DelegateCollect = DelegateCollect()
collect.delegate = delegate

collect.replace(newDict: ["1":1, "2":2 ,"3":3])
collect.replace(newDict: ["2":2, "3":3 ,"4":4])
collect.applyLast()
collect.applyLast()