Validate Singapore NRIC

SingaporeNRICValidator.swift

func validateSingaporeNRIC(_ nricString: String) -> Bool {
    let str = nricString.uppercased()
    let characters = [Character](str)
    if characters[0] == "M" {
        return true
    }
    guard str.count == 9 else { return false }

    var weight  = 0

    weight += String(characters[1]) == " " ? 0 : (Int(String(characters[1])) ?? 0) * 2
    weight += String(characters[2]) == " " ? 0 : (Int(String(characters[2])) ?? 0) * 7
    weight += String(characters[3]) == " " ? 0 : (Int(String(characters[3])) ?? 0) * 6
    weight += String(characters[4]) == " " ? 0 : (Int(String(characters[4])) ?? 0) * 5
    weight += String(characters[5]) == " " ? 0 : (Int(String(characters[5])) ?? 0) * 4
    weight += String(characters[6]) == " " ? 0 : (Int(String(characters[6])) ?? 0) * 3
    weight += String(characters[7]) == " " ? 0 : (Int(String(characters[7])) ?? 0) * 2
    if characters.first == "T" || characters.first == "G" {
        weight += 4
    }
    let temp = weight % 11
    let st = ["J", "Z", "I", "H", "G", "F", "E", "D", "C", "B", "A"]
    let fg = ["X", "W", "U", "T", "R", "Q", "P", "N", "M", "L", "K"]
    var theAlpha: String?
    if characters.first == "S" || characters.first == "T" {
        theAlpha = st[temp]
    } else if characters.first == "F" || characters.first == "G" {
        theAlpha = fg[temp]
    }
    if String(characters[8]) == theAlpha {
        return true
    }
    return false
}

print(validateSingaporeNRIC("S8473912z"))