LocalStorageType.swift

// MARK: - LocalStorageType

protocol LocalStorageType {
  func storageKey<Element: Storable>(of type: Element.Type) -> String

  @discardableResult func append<Element: Storable>(_ value: Element) -> Bool
  func element<Element: Storable>(of type: Element.Type) -> Element?
  func array<Element: Storable>(of type: Element.Type) -> [Element]
  @discardableResult func update<Element: Storable>(_ value: Element) -> Bool
  @discardableResult func remove<Element: Storable>(_ value: Element) -> Bool
}

extension LocalStorageType {
  func storageKey<Element>(of type: Element.Type) -> String {
    [
      "dev.jsryu.LocalStorage",
      String(describing: type)
    ]
    .joined(separator: ".")
  }

  func element<Element: Storable>(
    of type: Element.Type = Element.self
  ) -> Element? {
    element(of: type)
  }

  func array<Element: Storable>(
    of type: Element.Type = Element.self
  ) -> [Element] {
    array(of: type)
  }
}

// MARK: - LocalStorage

final class LocalStorage: LocalStorageType {
  private let decoder: JSONDecoder
  private let encdoer: JSONEncoder

  private let storage: UserDefaults
  init(storage: UserDefaults = .standard) {
    self.storage = storage
    self.decoder = JSONDecoder()
    self.encdoer = JSONEncoder()
  }

  @discardableResult
  func append<Element: Storable>(_ value: Element) -> Bool {
    var elements = loadData(of: [Element].self) ?? []
    elements.append(value)
    saveData(elements)
    return true
  }

  func element<Element: Storable>(of type: Element.Type) -> Element? {
    let element = loadData(of: type)
    return element
  }

  func array<Element: Storable>(of type: Element.Type) -> [Element] {
    let elements = loadData(of: [Element].self) ?? []
    return elements
  }

  @discardableResult
  func update<Element: Storable>(_ value: Element) -> Bool {
    saveData(value)
    return true
  }

  @discardableResult
  func remove<Element: Storable>(_ value: Element) -> Bool {
    var elements = loadData(of: [Element].self) ?? []
    if let index = elements.firstIndex(where: { $0.hashValue == value.hashValue }) {
      elements.remove(at: index)
      saveData(elements)
      return true
    } else {
      return false
    }
  }
}

extension LocalStorage {
  private func loadData<Element: Decodable>(of type: Element.Type) -> Element? {
    guard let data = storage.object(forKey: storageKey(of: type)) as? Data else {
      return nil
    }

    let element = try? decoder.decode(Element.self, from: data)
    return element
  }

  private func saveData<Element: Encodable>(_ element: Element) {
    guard let data = try? encdoer.encode(element) else {
      return
    }

    storage.setValue(
      data,
      forKey: storageKey(of: Element.self)
    )
  }
}