NSUserDefaults abstraction

gistfile1.swift

//
//  Storage.swift
//
//  Created by Martin Conte Mac Donell (Reflejo@gmail.com)
//

import Foundation

/**
This struct is the base for Storage Keys. This way we enforce all keys to be in a container to avoid typos
when using strings that are evaluated at runtime.
*/
public struct StorageKey: RawRepresentable {
    public var rawValue: String
    public init(rawValue value: String) {
        self.rawValue = value
    }

    public init(_ value: String) {
        self.rawValue = value
    }
}

/**
This struct serves as a wrapper to NSUserDefaults. The idea is to abstract the device storage in order to
make storing data more flexible and modular. All keys should be set on the struct above.
*/
public struct Storage {

    /**
    Returns the object associated with the first occurrence of the specified key or the defaultValue if the
    key is not found.

    :param: key          A key from the StorageKey enum.
    :param: defaultValue The default value that is going to be returned if the key is not found.

    :returns: The object associated with the specified key, or defaultValue if the key was not found.
    */
    public static func get<T>(key: StorageKey, defaultValue: T) -> T {
        return NSUserDefaults.standardUserDefaults().objectForKey(key.rawValue) as? T ?? defaultValue
    }

    /**
    Returns the object associated with the first occurrence of the specified key.

    :param: key          A key from the StorageKey enum.

    :returns: The object associated with the specified key, or nil if the key was not found.
    */
    public static func get<T>(key: StorageKey) -> T? {
        return NSUserDefaults.standardUserDefaults().objectForKey(key.rawValue) as? T
    }

    /**
    Sets the value of the specified default key in the standard application domain.

    :param: value The object to store in the defaults database if nil the key will get removed.
    :param: key   The key (from the StorageKey enum) with which to associate with the value.
    */
    public static func set(value: AnyObject?, forKey key: StorageKey) {
        if value == nil {
            return NSUserDefaults.standardUserDefaults().removeObjectForKey(key.rawValue)
        }

        NSUserDefaults.standardUserDefaults().setObject(value, forKey: key.rawValue)
    }

    /**
    Writes any modifications to the persistent domains to disk and updates all unmodified persistent
    domains to what is on disk.
    */
    public static func sync() {
        NSUserDefaults.standardUserDefaults().synchronize()
    }

    /**
    Removes all keys and values stored in the application domain (all of them).
    */
    public static func removeAll() {
        let appDomain = NSBundle.mainBundle().bundleIdentifier!
        NSUserDefaults.standardUserDefaults().removePersistentDomainForName(appDomain)
    }
}

// MARK: - Example

extension StorageKey {
    static let KeyA = StorageKey("A")
    static let KeyB = StorageKey("B")
    static let KeyC = StorageKey("C")
}

Storage.set(1, forKey: .KeyA)
println(Storage.get(.KeyA) as Int?)
println(Storage.get(.KeyB, defaultValue: 0))

Storage.set([1, 2, 3], forKey: .KeyB)
println(Storage.get(.KeyB) as [Int]?)

Storage.set(NSData(), forKey: .KeyC)
println(Storage.get(.KeyC) as NSData?)

// Output:
// Optional(1)
// 0
// Optional([1, 2, 3])
// Optional(<>)