@protocol SKComponent <NSObject>

@property (nonatomic, readwrite) BOOL enabled;

@optional
@property (nonatomic, weak) SKNode *node;

@optional
// triggered when the component is added to a component node
- (void)awake;

// when the node is added to the scene
- (void)onEnter;

// when the node is removed from the scene
- (void)onExit;

// called every frame. dt = time since last frame
- (void)update:(CFTimeInterval)dt;

// SpriteKit - forwarded from SKScene
- (void)onSceneSizeChanged:(CGSize)oldSize;

// SpriteKit - forwarded from SKScene
- (void)didEvaluateActions;

#pragma mark -- Physics Handlers --

// SpriteKit - forwarded from SKScene
- (void)didSimulatePhysics;

// SpriteKit - forwarded from SKScene when this node is one of the nodes in contact
- (void)didBeginContact:(SKPhysicsContact *)contact;
- (void)didEndContact:(SKPhysicsContact *)contact;


#pragma mark -- Touch Handlers --
// all touch handlers are only triggered if the tough down is inside the node content area

// called once a touch moves beyond the SKComponentNode dragThreshold (defaults to 4 units)
- (void)dragStart:(SKCTouchState*)touchState;

// called every time a touch moves after dragging has started
- (void)dragMoved:(SKCTouchState*)touchState;

// called on touch up after dragging has started
- (void)dragDropped:(SKCTouchState*)touchState;

// called if the touch is canceled after dragging has started
- (void)dragCancelled:(SKCTouchState*)touchState;
- 

// called on Touch Up if UITouch tap count >= 1 and touch is not classified as dragging or a long touch
- (void)onTap:(SKCTouchState*)touchState;

// called if touch is held for SKComponentNode longPressTime (defaults to 1 second)
// AND touch has not moved beyond dragThreshold
- (void)onLongPress:(SKCTouchState*)touchState;

// equivalent to iOS Touch Up Inside. Typically used for menu items rather than tap
- (void)onSelect:(SKCTouchState*)touchState;


// standard touchesBegan event, called prior to touchState based events
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;

// standard touchesMoved event, called prior to touchState based events
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event;

// standard touchesEnded event, called prior to touchState based events
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event;

// standard touchesCancelled event, called prior to touchState based events
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event;


@end

@interface SKCDeepAlpha : NSObject<SKComponent> {
    float previousAlpha;
}
@end

#import "SKCDeepAlpha.h"

@implementation SKCDeepAlpha
@synthesize node,enabled;

- (void)onEnter {
    recursivelyApplyAlpha(node, node.alpha);
}

- (void)didEvaluateActions {
    if (previousAlpha != node.alpha) {
        recursivelyApplyAlpha(node, node.alpha);
        previousAlpha = node.alpha;
    }
}

void recursivelyApplyAlpha(SKNode* node, float alpha) {
    for (SKNode *child in node.children) {
        child.alpha = alpha;
        if (child.children.count > 0)
            recursivelyApplyAlpha(child, alpha);
    }
}
@end

SKNode* node = [SKComponentNode node];
[node addComponent:[SKCDeepAlpha new]];
// add sprites or shapes as children of your node, then add it to the scene
[scene addChild:node];

@implementation SKCSelectTest
@synthesize node, enabled;

- (void)awake {
    node.userInteractionEnabled = YES;
}

- (void)onSelect:(SKCTouchState*)touchState {
    // do something
}
@end

@implementation SKCDraggable
@synthesize node, enabled;
@synthesize startPosition;

- (void)awake {
    node.userInteractionEnabled = YES;
}

- (void)dragStart:(SKCTouchState*)touchState {
    // we could do something here to clue the user in on the fact that we started dragging
    startPosition = node.position;
}

- (void)dragMoved:(SKCTouchState*)touchState {
    // check out the skHelper.m for a couple shorthand functions/methods for vector` math
    node.position = skpAdd(node.position, touchState.touchLocation);
}

- (void)dragDropped:(SKCTouchState*)touchState {
    // we could show the user we dropped successfully here
}

- (void)dragCancelled:(SKCTouchState*)touchState {
    node.position = startPosition;
}
@end

// Disable the component of type MyComponent (callbacks will immediately stop)
[node getComponent:[MyComponent class]].enabled = NO;

// or better yet, get the component casted to the proper type
SKGetComponent(node, MyComponent).customProperty = 42;

[node addComponent:[SpeedDoubler new] withName:@"2xSpeed"];
[node addComponent:[SpeedDoubler new] withName:@"4xSpeed"];
[node getComponentWithName:@"4xSpeed"].enabled = NO;