using System;
using Grid;
using UnityEngine;
using UnityEngine.EventSystems;

namespace Actions {
    public class UnitActionSystem : MonoBehaviour {
        [SerializeField] private LayerMask UnitsLayerMask;
        [SerializeField] private Unit selectedUnit;

        public static UnitActionSystem Instance { get; private set; }
        private bool IsBusy { get; set; }
        public BaseAction SelectedAction { get; private set; }

        public Unit SelectedUnit {
            get => selectedUnit;
            private set => selectedUnit = value;
        }

        private void Awake() {
            if (Instance is not null) {
                Debug.LogError($"There is more than one UnitActionSystem! {transform} - {Instance}");
                Destroy(gameObject);
                return;
            }

            Instance = this;
        }

        private void Start() => SetSelectedUnit(SelectedUnit);

        private void Update() {
            if (IsBusy) return;
            if (EventSystem.current.IsPointerOverGameObject()) return;
            if (TryHandleUnitSelection()) return;
            if (SelectedUnit is not null) HandleSelectedAction();
        }

        private void HandleSelectedAction() {
            if (!Input.GetMouseButtonDown(0)) return;

            GridPosition mouseGridPosition = LevelGrid.Instance.GetGridPosition(MouseWorld.GetPosition());
            if (!SelectedAction.IsValidActionGridPosition(mouseGridPosition)) return;

            IsBusy = true;
            SelectedAction.TakeAction(mouseGridPosition, ClearBusy);
        }

        private void ClearBusy() => IsBusy = false;

        public event EventHandler OnSelectedUnitChanged;
        public event EventHandler OnSelectedActionChanged;

        private bool TryHandleUnitSelection() {
            if (!Input.GetMouseButtonDown(0)) return false;
            if (!Physics.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), out RaycastHit raycastHit, float.MaxValue, UnitsLayerMask)) return false;
            if (!raycastHit.transform.TryGetComponent(out Unit unit) || unit is null) return false;
            if (unit == selectedUnit) return false;

            SetSelectedUnit(unit);
            return true;
        }

        private void SetSelectedUnit(Unit unit) {
            SelectedUnit = unit;
            SelectedAction = unit.MoveAction;
            OnSelectedUnitChanged?.Invoke(this, EventArgs.Empty);
        }

        public void SetSelectedAction(BaseAction baseAction) {
            SelectedAction = baseAction;
            OnSelectedActionChanged?.Invoke(this, EventArgs.Empty);
        }
    }
}