namespace Wayne.Lib.StateEngine.Generic
{
    /// <summary>
    /// Generic composite state class that has a main object of a generic type.
    /// </summary>
    /// <typeparam name="TMain">Specifies the type of the main object.</typeparam>
    /// <typeparam name="TData">Specifies the type of state data the state uses.</typeparam>
    public abstract class CompositeState<TMain, TData> : CompositeState<TMain>, IStateWithData where TData : StateData
    {
        #region Fields

        private TData data;
        private IStateWithData stateWithData;

        #endregion

        #region Properties

        /// <summary>
        /// Gets the state data for this state.
        /// </summary>
        protected TData Data
        {
            get
            {
                if (data != null) // Do I have my own data?
                    return data;
                else // Otherwise, unwind from parent composite states.
                    return stateWithData.StateData as TData;
            }
        }

        StateData IStateWithData.StateData
        {
            get { return Data; }
        }

        #endregion

        #region Methods

        internal override void PerformEnter(StateEntry stateEntry, ref Transition transition)
        {
            InitStateData();

            base.PerformEnter(stateEntry, ref transition);
        }

        internal override void PerformExit()
        {
            base.PerformExit();

            using (data) //Dispose without risk for nullref exceptions
            {
                data = null;
            }
        }

        /// <summary>
        /// CreateStateData method should be overridden by those composite states that does not have the same state data 
        /// as their parent state.
        /// </summary>
        /// <param name="parentStateData"></param>
        /// <returns></returns>
        protected virtual TData CreateStateData(StateData parentStateData)
        {
            return null;
        }

        private void InitStateData()
        {
            //Create the state data for this composite state. 
            //The composite state has the option to return null, if it wants to use a parent composite state's data object. 
            var compositeStateWithData = ParentState as IStateWithData;
            if (compositeStateWithData != null)
                data = CreateStateData(compositeStateWithData.StateData); //Create state data before enter method of state gets called.
            else
                data = CreateStateData(null);

            if (data == null)
            {
                if (stateWithData == null)
                {
                    stateWithData = StateData.GetParentCompositeStateWithStateData<TData>(this);
                }
            }
        }

        #endregion
    }
}