initial work on enemy behavior

Assets/Scripts/Enemy.cs

@@ -1,11 +1,187 @@
+using RuntimeSet;
 using UnityEngine;
+using UnityEngine.Assertions;
 
 namespace DefaultNamespace
 {
-    // TODO (Michael): Empty behavior until we decide more on how enemies should be structured. Mainly being used for 
-    // other systems to have something to reference.
     public class Enemy : MonoBehaviour
     {
-        
+        private enum BehaviorState
+        {
+            Create,
+            Spawning,
+            Chasing,
+            Attacking,
+            Feared,
+            Dead,
+        }
+
+        [SerializeField] private EnemyAttributesSO attributes;
+        [SerializeField] private EnemyRuntimeSetSO enemySet;
+        [SerializeField] private HeroUnitRuntimeSetSO heroSet;
+        [SerializeField] private GameObject target;
+        // TODO(zeph): Having behavior as a serialized member is convenient for
+        // experimentation early on so we can change it mid-play through the
+        // inspector, but later we'll more likely want it to be a property.
+        [SerializeField] private BehaviorState _behavior = BehaviorState.Spawning;
+        [SerializeField] private float _behaviorTime = 0;
+        [SerializeField] private float _fear = 0;
+        [SerializeField] private long _hp;
+
+        private void Update()
+        {
+            // When the current behavior indicates movement, we do it in Update
+            // to ensure it is smooth at all framerates.
+            if (_behavior != BehaviorState.Chasing && _behavior != BehaviorState.Feared)
+            {
+                // No movement.
+                return;
+            }
+            if (target == null)
+            {
+                // No target. Find a new one.
+                Retarget();
+                return;
+            }
+            // TODO(zeph): how do we actually,, get SPD attribute
+            var spd = SpaceSpeed(1000, Time.deltaTime);
+            var to = Vector3.MoveTowards(transform.position, target.transform.position, spd);
+            if (_behavior == BehaviorState.Feared)
+            {
+                // Move away rather than toward.
+                // TODO(zeph): this will limit speed moving away by distance
+                // to target if we're close
+                to = transform.position - 2 * (transform.position - to);
+            }
+            transform.position = to;
+        }
+
+        private void FixedUpdate()
+        {
+            // We do behavior changes in the fixed update so that enemy actions
+            // do not depend on the framerate. Since movement happens in
+            // Update, the overall effect as framerate varies is that enemies
+            // might change their behaviors at slightly different distances,
+            // but they'll always be in a given state for the same duration.
+            // TODO(zeph): we could probably do this with coroutines instead,
+            // also i still haven't read anything about the actual fsm system
+            _behaviorTime += Time.fixedDeltaTime;
+            float dd;
+            switch (_behavior)
+            {
+                case BehaviorState.Create:
+                    // TODO(zeph): calculate starting hp from CON attribute
+                    _hp = 1;
+                    SetBehavior(BehaviorState.Spawning);
+                    break;
+                case BehaviorState.Spawning:
+                    // TODO(zeph): move spawn time to an asset
+                    if (_behaviorTime >= 0.5)
+                    {
+                        Retarget();
+                        SetBehavior(BehaviorState.Chasing);
+                    }
+                    break;
+                case BehaviorState.Chasing:
+                    dd = SquareDistanceToTarget();
+                    // TODO(zeph): RNG attribute
+                    if (dd <= SpaceRange(20000))
+                    {
+                        SetBehavior(BehaviorState.Attacking);
+                    }
+                    break;
+                case BehaviorState.Attacking:
+                    dd = SquareDistanceToTarget();
+                    if (dd > SpaceRange(20000))
+                    {
+                        SetBehavior(BehaviorState.Chasing);
+                    }
+                    break;
+                case BehaviorState.Feared:
+                    if (_behaviorTime > _fear)
+                    {
+                        SetBehavior(BehaviorState.Chasing);
+                    }
+                    break;
+                case BehaviorState.Dead:
+                    // do nothing
+                    break;
+                default:
+                    // TODO(zeph): unreachable
+                    break;
+            }
+            if (_behavior != BehaviorState.Dead && _hp == 0)
+            {
+                SetBehavior(BehaviorState.Dead);
+                // TODO(zeph): put a dead time constant somewhere
+                Destroy(gameObject, 10f);
+            }
+        }
+
+        private void OnEnable()
+        {
+            Assert.IsNotNull(enemySet);
+            enemySet.Add(this);
+        }
+
+        private void OnDisable()
+        {
+            enemySet.Remove(this);
+        }
+
+        private void Retarget()
+        {
+            if (heroSet == null || heroSet.Count == 0)
+            {
+                // No heroes to target.
+                // TODO(zeph): switch to a special behavior?
+                target = null;
+                return;
+            }
+            // TODO(zeph): target based on threat, once threat exists
+            var k = Random.Range(0, heroSet.Count);
+            var it = heroSet.GetEnumerator();
+            // This seems to be the best way to do this...?
+            for (var i = 0; i < k; i++)
+            {
+                it.MoveNext();
+            }
+            target = it.Current.gameObject;
+        }
+
+        private void SetBehavior(BehaviorState behavior)
+        {
+            _behavior = behavior;
+            _behaviorTime = 0;
+        }
+
+        private float SquareDistanceToTarget()
+        {
+            return Vector3.Magnitude(transform.position - target.transform.position);
+        }
+
+        public void Fear(float dur)
+        {
+            // If the enemy is already feared for a longer duration, don't
+            // shorten it.
+            if (_behavior == BehaviorState.Feared && _fear - _behaviorTime >= dur)
+            {
+                return;
+            }
+            _fear = dur;
+            SetBehavior(BehaviorState.Feared);
+        }
+
+        private static float SpaceSpeed(long spd, float dt)
+        {
+            // For now, treat SPD as units of ten thousandths of a unit per second.
+            return (spd / 10000) * dt;
+        }
+
+        private static float SpaceRange(long rng)
+        {
+            // Treat RNG as units of ten thousandths of a sqrt-meter.
+            return rng / 10000;
+        }
     }
-}
+}