using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Events;

/// <summary>
/// Manages selection state for placed interactable objects.
/// Listens to RayInteractor.OnSelectEvent (which only fires when no ghost is active).
/// Supports single and multi-select (Ctrl/Shift).
/// </summary>
public class SelectionManager : MonoBehaviour
{
    private static SelectionManager instance;
    public static SelectionManager getInstance() => instance;

    private RayInteractor rayInteractor;
    private BaseInputProvider inputProvider;

    private readonly List<IInteractable> currentSelections = new List<IInteractable>();
    private bool multiSelectEnabled = false;

    public UnityEvent<IInteractable> SelectionEvent;

    // -------------------------------------------------------------------------
    // Unity lifecycle
    // -------------------------------------------------------------------------

    private void Awake()
    {
        if (instance == null) instance = this;
        else Destroy(gameObject);
    }

    private void Start()
    {
        rayInteractor = RayInteractor.getInstance();
        inputProvider = InputProviderManager.getInstance().getCurrentInputProvider();

        inputProvider.OnEnableMultiSelect.AddListener(() => multiSelectEnabled = true);
        inputProvider.OnDisableMultiSelect.AddListener(() => multiSelectEnabled = false);

        // RayInteractor only fires this when no ghost is active, so we can safely handle selection here
        rayInteractor.OnSelectEvent.AddListener(HandleSelect);
    }

    // -------------------------------------------------------------------------
    // Selection logic
    // -------------------------------------------------------------------------

    private void HandleSelect(IInteractable interactable)
    {
        if (InputModeManager.Is(InputMode.UI)) return;
        if (interactable == null)
        {
            SelectionEvent?.Invoke(interactable);
            // Clicked empty space – clear selection unless multi-select is held
            if (!multiSelectEnabled)
                ClearSelection();
            return;
        }

        if (multiSelectEnabled)
        {
            // Toggle the clicked interactable
            if (currentSelections.Contains(interactable))
            {
                currentSelections.Remove(interactable);
                interactable.highLightOff();
            }
            else
            {
                currentSelections.Add(interactable);
                interactable.highLightOn();
            }
        }
        else
        {
            // Replace selection with just this interactable
            bool Exists = currentSelections.Contains(interactable);
            ClearSelection();
            if (!Exists) {
                currentSelections.Add(interactable);
                interactable.highLightOn();
            }
        }
        SelectionEvent?.Invoke(interactable);
    }

    // -------------------------------------------------------------------------
    // Public API
    // -------------------------------------------------------------------------

    public List<IInteractable> GetCurrentSelections() => currentSelections;

    public void ClearSelection()
    {
        foreach (IInteractable selection in currentSelections)
            selection.highLightOff();

        currentSelections.Clear();
        SelectionEvent?.Invoke(null);
    }

    public bool HasOneSelection()
    {
        return !(currentSelections.Count > 1 || currentSelections.Count == 0);
    }
}