Regular Expression using Swift

String.swift

import UIKit

extension String {
    func regex(_ pattern: String) -> Int {
        let results: [Int] = self.regex(pattern)
        guard let item = results.first, results.count > 0 else {
            return NSNotFound
        }
        
        return item
    }
    
    func regex(_ pattern: String) -> [Int] {
        
        if let expression = try? NSRegularExpression(pattern: pattern, options: .caseInsensitive) {
            let results = expression.matches(in: self, options: .reportCompletion, range: NSRange(location: 0, length: self.characters.count))
            
            let contents: [Int] = results.flatMap({
                
                let value = (self as NSString).substring(with: $0.rangeAt(1))
                
                let numberFormatter = NumberFormatter()
                if let number = numberFormatter.number(from: value) {
                    return number.intValue
                }
                
                return nil
            })
            
            return contents
        }
        
        return []
    }
}

let pattern = "SE-([0-9]+)"
let ids = "SE-8740, SE-8741, SE-8742, SE-8743, SE-8744, SE-8745, SE-8746, SE-8747"

let test1: [Int] = ids.regex(pattern)
print(test1)

let test2: Int = ids.regex(pattern)
print(test2)

let test3: Int = "SE-0140".regex(pattern)
print(String(format: "SE-%04i", test3))