NSRegex.swift

final class NSRegex {
    
    private let regex:NSRegularExpression
    private let subject:String
    private var matches:[NSTextCheckingResult] = []
    
    init(regex:NSRegularExpression, subject:String) {
        self.regex = regex
        self.subject = subject
        matches = regex.matches(in: subject, range: NSRange(location: 0, length: subject.count))
    }
    
    func valueForCaptureGroup(at index:Int) -> String? {
        guard let match = matches.first else { return nil}
        if index < match.numberOfRanges { return nil }
        let range = match.range(at: index)
        return value(forRange: range)
    }
    
    func valueForNamedCaptureGroup(_ named:String) -> String? {
        guard let match = matches.first else { return nil }
        let range = match.range(withName: named)
        return value(forRange: range)
    }
    
    private func value(forRange range:NSRange) -> String? {
        let startIndex = subject.index(subject.startIndex, offsetBy: range.location)
        let endIndex = subject.index(startIndex, offsetBy: range.length)
        let strIndexRange = startIndex..<endIndex
        return String(subject[strIndexRange])
    }
}