Fields (email, password, set password, form, etc.) validators. Based on WWDC2014 session #229. I'm still working on this.

UBIFormValidators.swift

import Foundation
 
protocol Validator {
    func validateWithError(error: NSErrorPointer) -> Bool
}
///////////////////////////////////////////////
// MARK: - PasswordValidator -
///////////////////////////////////////////////
class PasswordValidator: Validator {
    
    //    init(password: String?) {
    //        input = password
    //    }
    
    var input: String?
    
    func validateWithError(error: NSErrorPointer) -> Bool {
        if let nonEmptyInput = input {
        var regexpError: NSError?
        if let regexp = NSRegularExpression(pattern: "[a-zA-Z0-9_]{4,}", options:NSRegularExpressionOptions(0), error:&regexpError) {
            
            let inputRange = NSRange(location:0, length:countElements(nonEmptyInput))
            let result = regexp.rangeOfFirstMatchInString(nonEmptyInput, options: .Anchored, range: inputRange)
            if result.location == NSNotFound  {
                // regexp validation failed
                // TODO: create error object for it
                return false
            }
                else {
                return true
            }
        }
            else {
            // regexp init error
            if error != nil { error.memory = regexpError }
            return false
        }
        }
        
        // empty input
        // Note: Regexp enforces to use at least 4 characters, so not-nil check might be not needed
        // TODO: create error object for it
        return false
    }
    
}
///////////////////////////////////////////////
// MARK: - UsernameValidator -
///////////////////////////////////////////////
// Note: the username here means e-mail
class UsernameValidator: Validator {
    
    var input: String?
    
    func validateWithError(error: NSErrorPointer) -> Bool {
        if let nonEmptyInput = input {
        let regexPattern = "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}"
        if let regexPredicate = NSPredicate(format:"SELF MATCHES %@", regexPattern) {
            let result = regexPredicate.evaluateWithObject(nonEmptyInput)
            // evaluating w/ regexp
            return result
        }
            else {
            // regexp creation error
            return false
        }
        }
        
        // empty input
        return false
    }
}
///////////////////////////////////////////////
// MARK: - SetPasswordValidator -
///////////////////////////////////////////////
class SetPasswordValidator: Validator {
    
    let firstPasswordValidator = PasswordValidator()
    let secondPasswordValidator = PasswordValidator()
    
    func validateWithError(error: NSErrorPointer) -> Bool {
        if firstPasswordValidator.validateWithError(nil) && secondPasswordValidator.validateWithError(nil) {
        if firstPasswordValidator.input == secondPasswordValidator.input {
            return true
        }
        }
        return false
    }
}
///////////////////////////////////////////////
// MARK: - SignIn Form Validator -
///////////////////////////////////////////////
// TODO: complete the form
class SignInFormValidator: Validator {
    func validateWithError(error: NSErrorPointer) -> Bool {
        return false
    }
}