TutorialRTS/Assets/Scripts/Unit.cs

using Unity.Mathematics;
using UnityEngine;
using UnityEngine.AI;
using UnityEngine.Events;

public enum UnitState
{
    Idle,
    Move,
    MoveToResource,
    Gather,
    MoveToEnemy,
    Attack
}

public class Unit : MonoBehaviour
{
    [Header("Components")]
    public GameObject selectionVisual;
    private NavMeshAgent navAgent;
    private SelectionMarker selectionMarker;
    [Header("Stats")]
    public UnitState state;
    public int gatherAmount;
    public float gatherRate;
    private float lastGatherTime;
    public int curHp;
    public int maxHp;
    public int minAttackDamage;
    public int maxAttackDamage;
    public float attackRate;
    private float lastAttackTime;
    public float pathUpdateRate = 1.0f;
    private float lastPathUpdateTime;
    private Unit curEnemyTarget;
    public float attackDistance;
    public UnitHealthBar healthBar;
    public ResourceSource curResourceSource;
    //events
    [System.Serializable]
    public class StateChangeEvent : UnityEvent<UnitState> { }
    public StateChangeEvent onStateChange;
    public Player player;

    [System.Obsolete]
    void Awake()
    {
        //get the components
        navAgent = GetComponent<NavMeshAgent>();
        SetState(UnitState.Idle);
    }
    // Start is called once before the first execution of Update after the MonoBehaviour is created
    void Start()
    {

    }

    // Update is called once per frame
    void Update()
    {
        if (selectionMarker != null && !navAgent.pathPending && navAgent.remainingDistance <= navAgent.stoppingDistance)
        {
            selectionMarker.DestroySelectionMarker();
            selectionMarker = null;
        }
        switch(state)
        {
            case UnitState.Move:
            {
                MoveUpdate();
                break;
            }
            case UnitState.MoveToResource:
            {
                MoveToResourceUpdate();
                break;
            }
            case UnitState.Gather:
            {
                GatherUpdate();
                break;
            }
            case UnitState.MoveToEnemy:
            {
                MoveToEnemyUpdate();
                break;
            }
            case UnitState.Attack:
            {
                AttackUpdate();
                break;
            }
        }
    }
    public void ToggleSelectionVisual(bool selected)
    {
        if(selectionVisual != null)
            selectionVisual.SetActive(selected);
    }
    public void MoveToPosition(Vector3 pos, SelectionMarker marker = null)
    {
        if (selectionMarker != null)
        {
            selectionMarker.DestroySelectionMarker();
            selectionMarker = null;
        }
        navAgent.isStopped = false;
        navAgent.SetDestination(pos);
        selectionMarker = marker;
        SetState(UnitState.Move);
    }
    //move to a resource and begin to gather it
    public void GatherResource(ResourceSource resource, Vector3 pos)
    {
        curResourceSource = resource;
        SetState(UnitState.MoveToResource);
        navAgent.isStopped = false;
        navAgent.SetDestination(pos);
    }
    void SetState(UnitState toState)
    {
        state = toState;
        //calling the event
        if(onStateChange != null)
            onStateChange.Invoke(state);
        if(toState == UnitState.Idle)
        {
            navAgent.isStopped = true;
            navAgent.ResetPath();
        }
    }
    void MoveUpdate()
    {
        if(!navAgent.pathPending && navAgent.remainingDistance <= navAgent.stoppingDistance)
            SetState(UnitState.Idle);
    }
    void MoveToResourceUpdate()
    {
        if(curResourceSource == null)
        {
            SetState(UnitState.Idle);
            return;
        }
        if(!navAgent.pathPending && navAgent.remainingDistance <= navAgent.stoppingDistance)
            SetState(UnitState.Gather);
    }
    void GatherUpdate()
    {
        if(curResourceSource == null)
        {
            SetState(UnitState.Idle);
            return;
        }
        LookAt(curResourceSource.transform.position);
        if(Time.time - lastGatherTime > gatherRate)
        {
            lastGatherTime = Time.time;
            curResourceSource.GatherResource(gatherAmount, player);
        }
    }
    //called every frame the "MoveToEnemy" state is active
    void MoveToEnemyUpdate()
    {
        if(curEnemyTarget == null)
        {
            SetState(UnitState.Idle);
            return;
        }
        if(Time.time - lastPathUpdateTime > pathUpdateRate)
        {
            lastPathUpdateTime = Time.time;
            navAgent.isStopped = false;
            navAgent.SetDestination(curEnemyTarget.transform.position);
        }
        if(Vector3.Distance(transform.position, curEnemyTarget.transform.position) <= attackDistance)
            SetState(UnitState.Attack);
    }
    //called every frame the "Attack" state is active
    void AttackUpdate()
    {
        //if our target is dead or null, go idle
        if(curEnemyTarget == null)
        {
            SetState(UnitState.Idle);
            return;
        }
        //if we are still moving
        if(!navAgent.isStopped)
            navAgent.isStopped = true;
        //attack every "attackRate" seconds
        if(Time.time - lastAttackTime > attackRate)
        {
            lastAttackTime = Time.time;
            curEnemyTarget.TakeDamage(UnityEngine.Random.Range(minAttackDamage, maxAttackDamage + 1));
        }
        //Look at the enemy
        LookAt(curEnemyTarget.transform.position);
        //if we are too far away, move towards the enemy
        if(Vector3.Distance(transform.position, curEnemyTarget.transform.position) > attackDistance)
            SetState(UnitState.MoveToEnemy);
    }
    //rotate to face the given position
    void LookAt(Vector3 pos)
    {
        Vector3 dir = (pos - transform.position).normalized;
        float angle = Mathf.Atan2(dir.x, dir.z) * Mathf.Rad2Deg;
        transform.rotation = Quaternion.Euler(0, angle, 0);
    }
    //move to an enemy unit and attack them
    public void AttackUnit(Unit target)
    {
        curEnemyTarget = target;
        SetState(UnitState.MoveToEnemy);
    }
    //called when we take damage from another unit
    public void TakeDamage(int damage)
    {
        curHp -= damage;
        if(curHp <= 0)
            Die();
        //update the health bar
        healthBar.UpdateHealthBar(curHp, maxHp);
    }
    //called when our health reaches 0
    void Die()
    {
        player.units.Remove(this);
        Destroy(gameObject);
    }
}