Get suffix number from file name

main.swift

import Foundation

extension String {
  func trimPrefix(_ prefix: String) -> String {
    guard self.hasPrefix(prefix) else {
      return self
    }

    return String(self.dropFirst(prefix.count))
  }
  func trimSuffix(_ suffix: String) -> String {
    guard self.hasSuffix(suffix) else {
      return self
    }

    return String(self.dropLast(suffix.count))
  }
}

extension URL {
  func getSuffixNumber(fileName: String, separator: String) -> Int {
    let a = self.lastPathComponent.trimPrefix(fileName + separator)

    if a == self.lastPathComponent {
      return -1
    }

    let b: String

    if self.pathExtension == "" {
      b = a
    } else {
      b = a.trimSuffix("." + self.pathExtension)
    }
    guard let n = Int(b) else {
      return -1
    }

    return n
  }
}

func main() {
  let urls: [URL] = [
    URL(fileURLWithPath: "/tmp/Hello World.txt"),
    URL(fileURLWithPath: "/tmp/Hello World 123.txt"),
    URL(fileURLWithPath: "/tmp/Goodbye 123.txt"),
    URL(fileURLWithPath: "/tmp/Hello World-456.txt"),
    URL(fileURLWithPath: "/tmp/Hello World_789.txt"),
    URL(fileURLWithPath: "/tmp/Hello World 777"),
    URL(fileURLWithPath: "/tmp/Hello World 777/abc 123.txt"),
  ]

  print("Number\tPath")

  for url in urls {
    print("\(url.getSuffixNumber(fileName: "Hello World", separator: " "))\t\(url.path)")
  }
}

main()