TransactionsViewModel

import UIKit
import SkeletonView

class TransactionsViewModel {

    private weak var viewController: TransactionHistoryViewController?
    private var networkManager: NetworkManagerType { NetworkManager.shared }
    private(set) var isLoading = false

    lazy var fromDate = toDate.addingTimeInterval(-3600 * 24 * 7)
    lazy var toDate = Date()

    private(set) var transactions: [Transaction]? {
        didSet {
            viewController?.tableView.backgroundLabelText = (transactions?.isEmpty ?? true) ? NSLocalizedString("NoOperationsForFilters") : nil
            viewController?.view.hideSkeleton(reloadDataAfter: true, transition: .crossDissolve(0.25))
            viewController?.tableView.reloadData()
        }
    }

    private var offset: Int = 0
    var filter: String? {
        didSet {
            transactions = nil
            offset = 0
            getTransactions()
        }
    }

    init(view: TransactionHistoryViewController) {
        self.viewController = view
    }

    func getTransactions(completion: (() -> ())? = nil) {
        isLoading = true
        networkManager.transactions(from: fromDate, to: toDate, pageSize: 50, offset: offset)
        { [weak self] (result) in
            self?.isLoading = false
            DispatchQueue.main.async {
                switch result {
                case .success(let transactions):
                    if self?.transactions == nil {
                        self?.onNilTransactions(transactions)
                    } else {
                        self?.onNotNilTransactions(transactions)
                    }
                case .failure:
                    self?.viewController?.tableView.backgroundLabelText = NSLocalizedString("Operation Failed. Try again.")
                    self?.viewController?.view.hideSkeleton(reloadDataAfter: true, transition: .crossDissolve(0.25))
                }
            }
            completion?()
        }
    }

    private func onNilTransactions(_ transactions: [Transaction]?) {
        guard let transactions = transactions else {
            self.viewController?.tableView.backgroundLabelText = NSLocalizedString("NoOperationsForFilters")
            self.viewController?.view.hideSkeleton(reloadDataAfter: true, transition: .crossDissolve(0.25))
            return
        }
        offset = transactions.count
        self.transactions = filter == nil ? getNAOperationTypeFilters(transactions) : getAllOperationTypeFilters(transactions)
    }

    private func onNotNilTransactions(_ transactions: [Transaction]?) {
        guard let transactions = transactions else { return }
        offset += transactions.count
        self.transactions?.append(contentsOf: filter == nil ? getNAOperationTypeFilters(transactions) : getAllOperationTypeFilters(transactions))
    }

    private func getNAOperationTypeFilters(_ transactions: [Transaction]) -> [Transaction] {
        return transactions.filter { $0.typeOfOperation != "NA" }
    }

    private func getAllOperationTypeFilters(_ transactions: [Transaction]) -> [Transaction] {
        return transactions.filter { $0.typeOfOperation != "NA" && $0.typeOfOperation == filter }
    }

    func clearTransactions() {
        transactions = nil
        offset = 0
    }
}