Fix arbitrary input strings into camelCasedWords [Swift 4]

NameFixer.swift

import Foundation

let sampleInputs = [
    "OAuth Token",
    "Hello-World!",
]

extension String {
    func capitalized() -> String {
        guard let firstCharacter = self.characters.first else { return "" }
        return self.replacingCharacters(in: (self.startIndex)...(self.startIndex), with: String(firstCharacter).uppercased())
    }
}

func fix(_ input: String) -> String {
    let words = input.split(whereSeparator: { character in
        return character == " " || character == "-"
    })
    var shouldCapitalizeNextWord: Bool = false
    let output = words.reduce("") { (output, word) -> String in
        let fixedWord = word.lowercased().trimmingCharacters(in: .punctuationCharacters)
        if shouldCapitalizeNextWord {
            return output.appending(fixedWord.capitalized())
        } else {
            shouldCapitalizeNextWord = true
            return output.appending(fixedWord)
        }
    }
    return output
}

let fixed = sampleInputs.map { fix($0) }
// [ "oauthToken", "helloWorld"]