Generates RedCarpet-compatible anchor text

markdown-anchor.swift

import Foundation

extension Character {
    var invalid: Bool {
        let invalid = Set(" -&+$,/:;=?@\"#{}|^~[]`\\*()%.!'".characters)
        return invalid.contains(self)
    }
    
    var isAscii: Bool {
        guard let number = String(self).utf16.first else { return false }
        return (65..<127) ~= number
    }
    
    var downcased: Character {
        if let downcased = String(self).lowercaseString.characters.first {
            return downcased
        }
        
        return self
    }
}

func anchor(header: String) -> String {
    var output = String(header.characters.map {
        var char = $0.downcased
        
        if $0.invalid || !$0.isAscii {
            char = "-"
        }
        
        return char
        })

    while output.containsString("--") {
        output = output.stringByReplacingOccurrencesOfString("--", withString: "-")
    }
    
    return output
}

let input = "How closely should my résumé mirror my LinkedIn profile?"

// prints how-closely-should-my-r-sum-mirror-my-linkedin-profile-
print(anchor(input))