Method to XOR multiple strings into one MD5 hexadecimal hash string in Swift 2. This means that [string1, string2, string3] gives the same MD5 hash as [string3, string2, string1]

MergeStringsIntoOneMD5Hash.swift

// Remember to #import <CommonCrypto/CommonCrypto.h> in the Bridging-Header.h file

/* Example of use
let query = "#test1 #test2 #test3"
let queryArray = query.characters.split{$0 == "#"}.map(String.init)
guard let hash = combineStringsIntoHash(queryArray) else{
    return
}
print("hash: \(hash)")
*/

func combineStringsIntoHash(stringsArray:[String]) -> String?{
        
      // If no strings are passed, return nil
      guard stringsArray.count > 0 else{
          return nil
      }
        
      // If only one string is passed there is no need to XOR
      if stringsArray.count == 1{
          return hex(md5(stringsArray[0]))
      }
        
      // If there are 2 strings or more, XOR the strings together to achieve one hash
      let hashArray:[[UInt8]] = stringsArray.map({md5($0)})
      // Get the array to start at index 1 rather than index 0 and use the value at index 0 as the initial value
      var subArray = hashArray
      subArray.removeFirst()

      return hex(subArray.reduce(hashArray[0], combine: {xor($0, hash2: $1)}))
 }
 
// Transform a string into an MD5 hash bytes array
private func md5(string: String) -> [UInt8] {
        
       // Make the string lowercase and remove all non-alphanumeric characters
      let nonAlphaNumericCharactersSet = NSCharacterSet.alphanumericCharacterSet().invertedSet
      let alphaNumericString = string.lowercaseString.componentsSeparatedByCharactersInSet(nonAlphaNumericCharactersSet).joinWithSeparator("")
        
      // Remove all accents - source: http://nshipster.com/cfstringtransform/
      let noAccentsString = NSMutableString(string: alphaNumericString) as CFMutableStringRef
      CFStringTransform(noAccentsString, nil, kCFStringTransformStripCombiningMarks, false)
        
      // Cast CFMutableString into NSString
      let cleanString = NSString(string: noAccentsString)
      print("cleanString: \(cleanString)")
        
      // Get the MD5 hash out of the string as a byte array [UInt8]
      var digest = [UInt8](count: Int(CC_MD5_DIGEST_LENGTH), repeatedValue: 0)
      if let data = cleanString.dataUsingEncoding(NSUTF8StringEncoding) {
          CC_MD5(data.bytes, CC_LONG(data.length), &digest)
      }
        
      return digest
}
    
// Combine 2 byte arrays into one using the XOR operation
private func xor(hash1:[UInt8], hash2:[UInt8]) -> [UInt8]{
        
      var xorArray:[UInt8] = []
      for i in 0..<hash1.count{
          xorArray.append(hash1[i] ^ hash2[i])
      }
      
      return xorArray
}
    
// Transform a byte array into an hex string
private func hex(hash:[UInt8]) -> String{
        
      var returnedHex = ""
        
      // Create the hex string, for example "63C6DD1FA19DA678C85BD4A4B65145 2"
      for byte in hash{
          returnedHex += NSString(format: "%2X", byte) as String
      }
        
      // If we have any spaces genererated from ' 0', we simply fill the spaces in with a 0
      // e.g. "63C6DD1FA19DA678C85BD4A4B6514502"
      return returnedHex.stringByReplacingOccurrencesOfString("\u{0020}", withString: "0")
}