using System;

namespace Unity.VisualScripting
{
    public abstract class StateTransition : GraphElement<StateGraph>, IStateTransition
    {
        public class DebugData : IStateTransitionDebugData
        {
            public Exception runtimeException { get; set; }

            public int lastBranchFrame { get; set; }

            public float lastBranchTime { get; set; }
        }

        protected StateTransition() { }

        protected StateTransition(IState source, IState destination)
        {
            Ensure.That(nameof(source)).IsNotNull(source);
            Ensure.That(nameof(destination)).IsNotNull(destination);

            if (source.graph != destination.graph)
            {
                throw new NotSupportedException("Cannot create transitions across state graphs.");
            }

            this.source = source;
            this.destination = destination;
        }

        public IGraphElementDebugData CreateDebugData()
        {
            return new DebugData();
        }

        public override int dependencyOrder => 1;

        [Serialize]
        public IState source { get; internal set; }

        [Serialize]
        public IState destination { get; internal set; }

        public override void Instantiate(GraphReference instance)
        {
            base.Instantiate(instance);

            if (this is IGraphEventListener listener && instance.GetElementData<State.Data>(source).isActive)
            {
                listener.StartListening(instance);
            }
        }

        public override void Uninstantiate(GraphReference instance)
        {
            if (this is IGraphEventListener listener)
            {
                listener.StopListening(instance);
            }

            base.Uninstantiate(instance);
        }

        #region Lifecycle

        public void Branch(Flow flow)
        {
            if (flow.enableDebug)
            {
                var editorData = flow.stack.GetElementDebugData<DebugData>(this);

                editorData.lastBranchFrame = EditorTimeBinding.frame;
                editorData.lastBranchTime = EditorTimeBinding.time;
            }

            try
            {
                source.OnExit(flow, StateExitReason.Branch);
            }
            catch (Exception ex)
            {
                source.HandleException(flow.stack, ex);
                throw;
            }

            source.OnBranchTo(flow, destination);

            try
            {
                destination.OnEnter(flow, StateEnterReason.Branch);
            }
            catch (Exception ex)
            {
                destination.HandleException(flow.stack, ex);
                throw;
            }
        }

        public abstract void OnEnter(Flow flow);

        public abstract void OnExit(Flow flow);

        #endregion
    }
}