using System;
using System.Threading;
using System.Threading.Tasks;

namespace LeanCloud.Storage.Internal {
  /// <summary>
  /// <code>IAVObjectCurrentController</code> controls the single-instance <see cref="AVObject"/>
  /// persistence used throughout the code-base. Sample usages are <see cref="AVUser.CurrentUser"/> and
  /// <see cref="AVInstallation.CurrentInstallation"/>.
  /// </summary>
  /// <typeparam name="T">Type of object being persisted.</typeparam>
  public interface IAVObjectCurrentController<T> where T : AVObject {
    /// <summary>
    /// Persists current <see cref="AVObject"/>.
    /// </summary>
    /// <param name="obj"><see cref="AVObject"/> to be persisted.</param>
    /// <param name="cancellationToken">The cancellation token.</param>
    Task SetAsync(T obj, CancellationToken cancellationToken);

    /// <summary>
    /// Gets the persisted current <see cref="AVObject"/>.
    /// </summary>
    /// <param name="cancellationToken">The cancellation token.</param>
    Task<T> GetAsync(CancellationToken cancellationToken);

    /// <summary>
    /// Returns a <see cref="Task"/> that resolves to <code>true</code> if current
    /// <see cref="AVObject"/> exists.
    /// </summary>
    /// <param name="cancellationToken">The cancellation token.</param>
    Task<bool> ExistsAsync(CancellationToken cancellationToken);

    /// <summary>
    /// Returns <code>true</code> if the given <see cref="AVObject"/> is the persisted current
    /// <see cref="AVObject"/>.
    /// </summary>
    /// <param name="obj">The object to check.</param>
    /// <returns>True if <code>obj</code> is the current persisted <see cref="AVObject"/>.</returns>
    bool IsCurrent(T obj);

    /// <summary>
    /// Nullifies the current <see cref="AVObject"/> from memory.
    /// </summary>
    void ClearFromMemory();

    /// <summary>
    /// Clears current <see cref="AVObject"/> from disk.
    /// </summary>
    void ClearFromDisk();
  }
}