gohan/component.go

package gohan

import "fmt"

// ComponentID is a component identifier. Each Component is assigned a unique ID
// via NextComponentID, and implements a ComponentID method which returns the ID.
type ComponentID int

// Component represents data for an entity, and how it interacts with the world.
type Component interface {
	ComponentID() ComponentID
}

var nextComponentID ComponentID

// NextComponentID returns the next available ComponentID.
func NextComponentID() ComponentID {
	id := nextComponentID
	nextComponentID++
	return id
}

func (entity EntityID) propagateChanges() {
	for i, system := range gameSystems {
		systemEntityIndex := -1
		for j, systemEntity := range gameSystemEntities[i] {
			if systemEntity == entity {
				systemEntityIndex = j
				break
			}
		}

		if system.Matches(entity) {
			if systemEntityIndex != -1 {
				// Already attached.
				continue
			}

			gameSystemEntities[i] = append(gameSystemEntities[i], entity)
			print(fmt.Sprintf("Attached entity %d to system %d.", entity, i))
		} else if systemEntityIndex != -1 {
			// Detach from system.
			gameSystemEntities[i] = append(gameSystemEntities[i][:systemEntityIndex], gameSystemEntities[i][systemEntityIndex+1:]...)
		}
	}
}

// AddComponent adds a Component to an Entity.
func (entity EntityID) AddComponent(component Component) {
	componentID := component.ComponentID()

	if gameComponents[entity] == nil {
		gameComponents[entity] = make(map[ComponentID]interface{})
	}
	gameComponents[entity][componentID] = component

	entity.propagateChanges()
}

// Component gets a Component of an Entity.
func (entity EntityID) Component(componentID ComponentID) interface{} {
	components := gameComponents[entity]
	if components == nil {
		return nil
	}
	return components[componentID]
}