NSUserDefaults with Wings!

import Palau

/// Your defaults are defined as extension of PalauDefaults
///
/// - The generic type of your PalauDefaultsEntry must conform 
///   to the protocol PalauDefaultable.
/// - We provide support for the most common types. 
/// - `value` is a helper function defined in PalauDefaults
/// - The String "backingName" is the key used in NSUserDefaults
/// - The empty `set` is used to please the compiler
extension PalauDefaults {
  /// a NSUserDefaults Entry of Type String with the key "backingName"
  public static var name: PalauDefaultsEntry<String> {
    get { return value("backingName") }
    set { }
  }
}

PalauDefaults.name.value = "I am a great String value!"

/// name is an Optional<String>
let name = PalauDefaults.name.value

PalauDefaults.name.value = nil

/// skip custom rules and delete
PalauDefaults.name.clear()

import Palau
extension PalauDefaults {
  public static var color: PalauDefaultsEntry<UIColor> {
    /// whenNil provides a value that will be returned
    /// when the related NSUserDefaults value is nil 
    /// (e.g. the 1st time, or after clear)
    get { return value("color").whenNil(use: UIColor.redColor())  }
    set { }
  }
}

/// is UIColor.redColor() 
let color: UIColor? = PalauDefaults.color.value

/// Custom Validator Closure
let lessThan10: Int? -> Bool = {
  return $0.map { $0 < 10 } ?? false
}

/// the PalauDefaultsEntry with the key "intValueMin10" has 2 rules
/// - 1. when the value is nil - we will get or set 10
/// - 2. when the value is less than 10 (see lessThan10 closure) - we will also get or set 10
/// - Add as many chainable rules as you like
public static var intValueMin10: PalauDefaultsEntry<Int> {
  get { return value("intValue")
    .whenNil(use: 10)
    .ensure(when: lessThan10, use: 10) }
  set { }
}

/// try setting the property to 8
PalauDefaults.intValueMin10.value = 8
/// property ensured to be >= 10
assert(PalauDefaults.intValueMin10.value == 10)
/// try setting the property to 11
PalauDefaults.intValueMin10.value = 11
/// property changed to 11
assert(PalauDefaults.intValueMin10.value == 11)

/// Extension for RawRepresentable types aka enums
extension PalauDefaultable where ValueType: RawRepresentable {

  public static func get(key: String, from defaults: NSUD) -> ValueType? {
    guard let val = defaults.objectForKey(key) as? ValueType.RawValue else { return nil }
    return ValueType(rawValue: val)
  }

  public static func set(value: ValueType?, forKey key: String, in defaults: NSUD) -> Void {
    guard let value = value?.rawValue as? AnyObject else { return defaults.removeObjectForKey(key) }
    defaults.setObject(value, forKey: key)
  }
}

/// Make UIColor PalauDefaultable
extension UIColor: PalauDefaultable {
  public typealias ValueType = UIColor
}

// example Struct called Structy for demonstrating we can save a Struct with Palau
public struct Structy {
  let tuple: (String, String)
}

// our Structy PalauDefaultable extension allowing the mapping between PalauDefaults and the Type
// here we just map the two values to two keys named "1" and "2"
extension Structy: PalauDefaultable {
  public static func get(key: String, from defaults: NSUD) -> Structy? {
    guard let d = defaults.objectForKey(key) as? [String: AnyObject] ,
      let t1 = d["1"] as? String,
      let t2 = d["2"] as? String else { return nil }
    return Structy(tuple: (t1, t2))
  }

  public static func set(value: Structy?, forKey key: String, in defaults: NSUD) -> Void {
    guard let value = value else { return defaults.setObject(nil, forKey: key) }
    defaults.setObject(["1": value.tuple.0, "2": value.tuple.1], forKey: key)
  }
}

// now create a property on PalauDefaults
extension PalauDefaults {
  public static var structWithTuple: PalauDefaultsEntry<Structy> {
    get { return value("structy") }
    set { }
  }
}

extension PalauDefaults {
  public static var strings: PalauDefaultsEntry<[String]> {
    get { return value("strings").didSet({ print("changed to:", $0, "from:", $1) }) }
    set { }
  }
}

typealias Defaults = PalauDefaults
typealias Defaultable = PalauDefaultable
/// for Swift 3 even:
/// typealias DefaultsEntry<T> = PalauDefaultsEntry<T>