using System.Collections.Generic;

namespace Engine.Core;

public class UniverseEntranceManager : Internal.BehaviourIndependent
{
    // We use Ascending order because we are using reverse for loop to call them
    private static Comparer<int> SortByAscendingPriority() => Comparer<int>.Create((x, y) => x.CompareTo(y));
    private static System.Func<IBehaviour, int> GetPriority() => (b) => b.Priority;

    private readonly ActiveBehaviourCollectorOrdered<int, IEnterUniverse> enterUniverses = new(GetPriority(), SortByAscendingPriority());
    private readonly ActiveBehaviourCollectorOrdered<int, IExitUniverse> exitUniverses = new(GetPriority(), SortByAscendingPriority());

    private bool isInitialCollectionDone = false;
    private readonly FastListOrdered<int, IEnterUniverse> toCallEnterUniverses = new(GetPriority(), SortByAscendingPriority());

    protected override void OnEnteredUniverse(IUniverse universe)
    {
        exitUniverses.Assign(universe);

        // FIXME: the isInitialCollectionDone is for the sole reason of some behaviours 
        // adding more behaviours during entrance calls and the internal workings of 
        // behaviour collector not being able to tell which behaviour was already called 
        // (because it just runs a for loop with the behaviour count, and priority ordering doesn't help as well) 
        // so it sometimes double processes or misses behaviours. A more elegant way of 
        // handling this would be nice but for now it works good enough.
        //
        // SIDE NOTE: This same issue has the potential to occur on exitUniverses as well, but I've yet to run 
        // into an instance of it actually happening so... I'm not gonna touch it until the edge case happens.  
        isInitialCollectionDone = false;
        enterUniverses.Assign(universe);
        isInitialCollectionDone = true;

        for (int i = toCallEnterUniverses.Count - 1; i >= 0; i--)
            toCallEnterUniverses[i].EnterUniverse(universe);
        toCallEnterUniverses.Clear();
    }

    protected override void OnExitedUniverse(IUniverse universe)
    {
        enterUniverses.Unassign();
        exitUniverses.Unassign();
    }

    private void OnEnterUniverseCollected(IBehaviourCollector<IEnterUniverse> sender, IBehaviourCollector<IEnterUniverse>.BehaviourCollectedArguments args)
    {
        if (!isInitialCollectionDone)
        {
            toCallEnterUniverses.Add(args.BehaviourCollected);
            return;
        }

        args.BehaviourCollected.EnterUniverse(Universe);
    }

    private void OnExitUniverseRemoved(IBehaviourCollector<IExitUniverse> sender, IBehaviourCollector<IExitUniverse>.BehaviourRemovedArguments args)
        => args.BehaviourRemoved.ExitUniverse(Universe);

    public UniverseEntranceManager()
    {
        enterUniverses.OnCollected.AddListener(OnEnterUniverseCollected);
        exitUniverses.OnRemoved.AddListener(OnExitUniverseRemoved);
    }
}