Custom iOS NumberFormatter Wrapper

NumberFormatter.swift

//
//  AppNumberFormatter.swift
//  TrumpWall
//
//  Created by Anton Poltoratskyi on 4/13/17.
//  Copyright © 2017 Anton Poltoratskyi. All rights reserved.
//

import Foundation

private let currencySymbol = "$"
private let thousandSymbol = "K"
private let millionSymbol = "M"
private let billionSymbol = "B"
private let groupingFormat = "###,###,###,###.##"

private enum FormatType: Int64 {
    case `default`  = 1
    case thousand   = 1_000
    case million    = 1_000_000
    case billion    = 1_000_000_000
    
    func convert(_ value: Double) -> Double {
        return value / Double(rawValue)
    }
}

class AppNumberFormatter {
    static let shared = AppNumberFormatter()
    private init() {}
    
    enum Style {
        case short      // display as '1K, 2.5M, 10B'
        case grouped    // display as '10,000,000,000'
    }
    
    // MARK: - Formatters
    
    private func baseNumberFormatter() -> NumberFormatter {
        let numberFormatter = NumberFormatter()
        numberFormatter.formatterBehavior = .default
        numberFormatter.usesGroupingSeparator = true
        numberFormatter.groupingSeparator = ","
        numberFormatter.currencyGroupingSeparator = ","
        numberFormatter.currencySymbol = currencySymbol
        return numberFormatter
    }
    
    // MARK: Default Grouped
    
    private lazy var currencyDefaultNumberFormatter: NumberFormatter = {
        let numberFormatter = self.baseNumberFormatter()
        numberFormatter.numberStyle = .currency
        numberFormatter.positiveFormat = "¤\(groupingFormat)"
        numberFormatter.negativeFormat = "-¤\(groupingFormat)"
        return numberFormatter
    }()
    private lazy var defaultNumberFormatter: NumberFormatter = {
        let numberFormatter = self.baseNumberFormatter()
        numberFormatter.numberStyle = .decimal
        numberFormatter.positiveFormat = "\(groupingFormat)"
        numberFormatter.negativeFormat = "-\(groupingFormat)"
        return numberFormatter
    }()
    
    // MARK: Thousand
    
    private lazy var currencyThousandNumberFormatter: NumberFormatter = {
        let numberFormatter = self.baseNumberFormatter()
        numberFormatter.numberStyle = .currency
        numberFormatter.positiveFormat = "¤\(groupingFormat)\(thousandSymbol)"
        numberFormatter.negativeFormat = "-¤\(groupingFormat)\(thousandSymbol)"
        return numberFormatter
    }()
    private lazy var thousandNumberFormatter: NumberFormatter = {
        let numberFormatter = self.baseNumberFormatter()
        numberFormatter.numberStyle = .decimal
        numberFormatter.positiveFormat = "\(groupingFormat)\(thousandSymbol)"
        numberFormatter.negativeFormat = "-\(groupingFormat)\(thousandSymbol)"
        return numberFormatter
    }()
    
    // MARK: Million
    
    private lazy var currencyMillionNumberFormatter: NumberFormatter = {
        let numberFormatter = self.baseNumberFormatter()
        numberFormatter.numberStyle = .currency
        numberFormatter.positiveFormat = "¤\(groupingFormat)\(millionSymbol)"
        numberFormatter.negativeFormat = "-¤\(groupingFormat)\(millionSymbol)"
        return numberFormatter
    }()
    private lazy var millionNumberFormatter: NumberFormatter = {
        let numberFormatter = self.baseNumberFormatter()
        numberFormatter.numberStyle = .decimal
        numberFormatter.positiveFormat = "\(groupingFormat)\(millionSymbol)"
        numberFormatter.negativeFormat = "-\(groupingFormat)\(millionSymbol)"
        return numberFormatter
    }()
    
    // MARK: Billion
    
    private lazy var currencyBillionNumberFormatter: NumberFormatter = {
        let numberFormatter = self.baseNumberFormatter()
        numberFormatter.numberStyle = .currency
        numberFormatter.positiveFormat = "¤\(groupingFormat)\(billionSymbol)"
        numberFormatter.negativeFormat = "-¤\(groupingFormat)\(billionSymbol)"
        return numberFormatter
    }()
    private lazy var billionNumberFormatter: NumberFormatter = {
        let numberFormatter = self.baseNumberFormatter()
        numberFormatter.numberStyle = .decimal
        numberFormatter.positiveFormat = "\(groupingFormat)\(billionSymbol)"
        numberFormatter.negativeFormat = "-\(groupingFormat)\(billionSymbol)"
        return numberFormatter
    }()
    
    private func numberFormatter(for value: Int64, style: Style, currency: Bool) -> (formatter: NumberFormatter, convertedValue: Double) {
        
        guard style == .short else {
            let formatter = currency ? currencyDefaultNumberFormatter : defaultNumberFormatter
            return (formatter: formatter, convertedValue: Double(value))
        }
        
        let formatter: NumberFormatter
        let convertedValue: Double
        
        let absoluteValue = abs(value)
        switch absoluteValue {
        case 0..<10_000:
            formatter = currency ? currencyDefaultNumberFormatter : defaultNumberFormatter
            convertedValue = FormatType.default.convert(Double(value))
        case 10_000..<1_000_000:
            formatter = currency ? currencyThousandNumberFormatter : thousandNumberFormatter
            convertedValue = FormatType.thousand.convert(Double(value))
        case 1_000_000..<1_000_000_000:
            formatter = currency ? currencyMillionNumberFormatter : millionNumberFormatter
            convertedValue = FormatType.million.convert(Double(value))
        default:
            formatter = currency ? currencyBillionNumberFormatter : billionNumberFormatter
            convertedValue = FormatType.billion.convert(Double(value))
        }
        return (formatter: formatter, convertedValue: convertedValue)
    }
    
    // MARK: - Public
    
    func format(value: Int64, style: Style = .short, currency: Bool = true) -> String {
        let (formatter, convertedValue) = self.numberFormatter(for: value, style: style, currency: currency)
        let result = formatter.string(for: convertedValue)
        return result ?? (value > 0 ? "\(currencySymbol)\(value)" : "-\(currencySymbol)\(value)")
    }
}