using System;

namespace Wayne.Lib.AsyncManager
{
    /// <summary>
    /// An Async Operation stores the necessary data for one asynchronous call. It has a 
    /// type parameter that represents what type of identifier the operation has, i.e. the type of
    /// sequence number, token etc.
    /// </summary>    
    public abstract class AsyncOperation<TOperationId>
    {
        #region Fields

        #endregion

        #region Events

        /// <summary>
        /// Internal event that is fired when the operation is completed. This will enable the AsyncManager to remove
        /// the operation from the list of outstanding operations.
        /// </summary>
        internal event EventHandler OnOperationCompleted;

        #endregion

        #region Construction

        /// <summary>
        /// Protected constructor of the AsyncOperation
        /// </summary>
        /// <param name="owner">The owner that will stand as sender when calling the delegate at completion.</param>
        /// <param name="id">Owner, that will stand as sender in the completion callback invocation.</param>
        /// <param name="userToken">User token to be supplied in the callback invocation.</param>
        /// <param name="data">User defined data.</param>
        internal protected AsyncOperation(object owner, TOperationId id, object userToken, object data):this(owner, id, userToken, data, ServiceContainerFactory.Create())
        {
        }

        /// <summary>
        /// Protected constructor of the AsyncOperation
        /// </summary>
        /// <param name="owner">The owner that will stand as sender when calling the delegate at completion.</param>
        /// <param name="id">Owner, that will stand as sender in the completion callback invocation.</param>
        /// <param name="userToken">User token to be supplied in the callback invocation.</param>
        /// <param name="data">User defined data.</param>
        /// <param name="serviceLocator"></param>
        internal protected AsyncOperation(object owner, TOperationId id, object userToken, object data, IServiceLocator serviceLocator)
        {
            ISystemTime systemTime = serviceLocator.GetServiceOrDefault<ISystemTime>(() => new WayneSystemTime());
            CreationDateTime = systemTime.Now;
            this.Owner = owner;
            this.Id = id;
            this.UserToken = userToken;
            this.Data = data;
        }

        #endregion

        #region Properties

        /// <summary>
        /// The owner of the operation. It will be set as the sender when calling the delegate at completion
        /// </summary>
        public object Owner { get; private set; }

        /// <summary>
        /// The identification for the operation.
        /// </summary>
        public TOperationId Id { get; private set; }

        /// <summary>
        /// The user token that identifies the operation.
        /// </summary>
        public object UserToken { get; private set; }

        /// <summary>
        /// Creation date time that enables a cleaning of the outstanding operation list.
        /// </summary>
        internal DateTime CreationDateTime { get; set; }

        /// <summary>
        /// User-defined data property that can be used to store application data with the operation.
        /// </summary>
        public object Data { get; set; }

        internal abstract Type ResultEventArgsType
        {
            get;
        }

        #endregion

        #region Methods

        /// <summary>
        /// Internal method to be called by descendant classes when the operation is completed and should be removed from the outstanding operations.
        /// </summary>
        internal protected void Complete()
        {
            if (OnOperationCompleted != null)
                OnOperationCompleted(this, EventArgs.Empty);
        }

        /// <summary>
        /// Removes the operation from the Async Manager lists, but does not call the completion delegate.
        /// </summary>
        public void Cancel()
        {
            Complete();
        }
        #endregion
    }

}