Function that "sanitizes" string to safe filename string that can be used on Mac, Linux and Windows.

StringSanitize.swift

var str = "2018/12/06 12:28 \\ - Ourdoor Run: Making a habbit.fgworkout"

extension String {
    func sanitized() -> String {
        // see for ressoning on charachrer sets https://superuser.com/a/358861
        let invalidCharacters = CharacterSet(charactersIn: "\\/:*?\"<>|")
            .union(.newlines)
            .union(.illegalCharacters)
            .union(.controlCharacters)
        
        return self
            .components(separatedBy: invalidCharacters)
            .joined(separator: "")
    }
    
    mutating func sanitize() -> Void {
        self = self.sanitized()
    }
    
    func whitespaceCondensed() -> String {
        return self.components(separatedBy: .whitespacesAndNewlines)
            .filter { !$0.isEmpty }
            .joined(separator: " ")
    }
    
    mutating func condenseWhitespace() -> Void {
        self = self.whitespaceCondensed()
    }
}

str.sanitized().whitespaceCondensed() // "20181206 1228 - Ourdoor Run Making a habbit.fgworkout"