TurnBasedStrategyCourse/Assets/Scripts/UnitActionSystem.cs

using System;
using UnityEngine;

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

    public static UnitActionSystem Instance { 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 Update() {
        if (Input.GetMouseButtonDown(0)) {
            if (TryHandleUnitSelection()) return;
            if (SelectedUnit is null) return;
            GridPosition mouseGridPosition = LevelGrid.Instance.GetGridPosition(MouseWorld.GetPosition());
            if (selectedUnit.MoveAction.IsValidActionGridPosition(mouseGridPosition)) SelectedUnit.MoveAction.Move(mouseGridPosition);
        }
    }

    public event EventHandler OnSelectedUnitChanged;

    private bool TryHandleUnitSelection() {
        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 not null) {
            SetSelectedUnit(unit);
            return true;
        }

        return false;
    }

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