gohan/entity.go

package gohan

import (
	"sync"
	"time"
)

// Entity is an entity identifier.
type Entity int

var maxEntityID Entity

var entityMutex sync.Mutex

// NewEntity returns a new (or previously removed and cleared) Entity. Because
// Gohan reuses removed Entity IDs, a previously removed ID may be returned.
func NewEntity() Entity {
	entityMutex.Lock()
	defer entityMutex.Unlock()

	if len(availableEntityIDs) > 0 {
		id := availableEntityIDs[0]
		availableEntityIDs = availableEntityIDs[1:]
		allEntities = append(allEntities, id)
		return id
	}

	maxEntityID++
	allEntities = append(allEntities, maxEntityID)
	gameComponents = append(gameComponents, make([]interface{}, maxComponentID+1))
	return maxEntityID
}

// Remove removes the provided Entity's components, causing it to no longer be
// handled by any system.  Because Gohan reuses removed EntityIDs, applications
// must also remove any internal references to the removed Entity.
func (entity Entity) Remove() {
	entityMutex.Lock()
	defer entityMutex.Unlock()

	for i, e := range allEntities {
		if e == entity {
			allEntities = append(allEntities[:i], allEntities[i+1:]...)
			removedEntities = append(removedEntities, e)
			return
		}
	}
}

var numEntities int
var numEntitiesT time.Time

// ActiveEntities returns the number of currently active entities.
func ActiveEntities() int {
	if time.Since(numEntitiesT) >= time.Second {
		numEntities = len(allEntities)
		numEntitiesT = time.Now()
	}
	return numEntities
}