Salesforce 15 character case sensitive Id to 18 character case insensitive Id in Swift 3

salesforce15to18.swift

import Foundation

extension String {
    func isUppercased(at: Index) -> Bool {
        let range = at..<self.index(after: at)
        return self.rangeOfCharacter(from: .uppercaseLetters, options: [], range: range) != nil
    }
}

extension Character {
    var isUppercase: Bool {
        let str = String(self)
        return str.isUppercased(at: str.startIndex)
    }
}

var ori = "005i0000001wr9E"


let lex = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U", "V","W","X","Y","Z","0","1","2","3","4","5"]

/*
 return a 1 character string converted from binary generated from count of uppercase characters
 */
func getSalesforceCharacterRepresentation(for id:String,with startOffset:Int, endOffset: Int) -> String? {
    
    let start = id.index(id.startIndex, offsetBy: startOffset)
    let end = id.index(id.endIndex, offsetBy: endOffset)
    let range = start..<end
    
    let subString = id.substring(with: range)
    
    
    var binaryString = ""
    for i in subString.characters.indices {
        if subString[i].isUppercase {
            binaryString += "1"
        } else {
            binaryString += "0"
        }
    }
    
    if let index = Int(String(binaryString.characters.reversed()), radix: 2) {
        return lex[index]
    }
    return nil
}

/*
 will convert a 15 character case sensitve Salesforce id to a 18 character case insensitive id
 */
func caseInsensitveSalesforceId(from id: String) -> String? {
    if id.characters.count == 18 { return id }
    if id.characters.count != 15 { return nil }
    
    let start = getSalesforceCharacterRepresentation(for: id, with: 0, endOffset: -10) ?? ""
    let middle = getSalesforceCharacterRepresentation(for: id, with: 5, endOffset: -5) ?? ""
    let end = getSalesforceCharacterRepresentation(for: id, with: 10, endOffset: 0) ?? ""
    
    let insensitiveId = id + start + middle + end
    
    if insensitiveId.characters.count == 18 { return insensitiveId }
    return nil
}

caseInsensitveSalesforceId(from: ori)