Add basic entity tracking, mob spawning and syncing

internal/world/entity.go

@@ -0,0 +1,77 @@
+package world
+
+import (
+	"crypto/rand"
+	"sync"
+	"sync/atomic"
+)
+
+// Entity represents an in-game movable entity (mob, animal, etc).
+type Entity struct {
+	ID       int32
+	UUID     [16]byte
+	TypeID   int   // Network ID from the minecraft:entity_type registry
+	TypeName string
+
+	X, Y, Z       float64
+	Pitch, Yaw    float32
+	HeadYaw       float32
+	VelocityX     int16
+	VelocityY     int16
+	VelocityZ     int16
+}
+
+// EntityManager tracks active entities in the server and manages thread-safe access.
+type EntityManager struct {
+	mu       sync.RWMutex
+	entities map[int32]*Entity
+	nextID   int32
+}
+
+// NewEntityManager returns a fresh manager starting at a high ID.
+func NewEntityManager() *EntityManager {
+	return &EntityManager{
+		entities: make(map[int32]*Entity),
+		nextID:   1000, // keep IDs above early players
+	}
+}
+
+// Add assigns an ID and UUID (if missing) and tracks the entity.
+func (em *EntityManager) Add(e *Entity) int32 {
+	em.mu.Lock()
+	defer em.mu.Unlock()
+	e.ID = atomic.AddInt32(&em.nextID, 1)
+	if e.UUID == [16]byte{} {
+		rand.Read(e.UUID[:])
+		// Version 4 UUID
+		e.UUID[6] = (e.UUID[6] & 0x0f) | 0x40
+		e.UUID[8] = (e.UUID[8] & 0x3f) | 0x80
+	}
+	em.entities[e.ID] = e
+	return e.ID
+}
+
+// Remove drops the entity by its ID.
+func (em *EntityManager) Remove(id int32) {
+	em.mu.Lock()
+	defer em.mu.Unlock()
+	delete(em.entities, id)
+}
+
+// Get retrieves an entity by ID, or nil if not found.
+func (em *EntityManager) Get(id int32) *Entity {
+	em.mu.RLock()
+	defer em.mu.RUnlock()
+	return em.entities[id]
+}
+
+// All returns a snapshot slice of all active entities.
+func (em *EntityManager) All() []*Entity {
+	em.mu.RLock()
+	defer em.mu.RUnlock()
+	list := make([]*Entity, 0, len(em.entities))
+	for _, e := range em.entities {
+		list = append(list, e)
+	}
+	return list
+}