setup_invades.m

-(void)setupInvaders {
    NSMutableArray *start = [NSMutableArray array];
    for (int i = 0; i < kInvaderRowCount*kInvaderColCount; ++i) {
        [start addObject:@(i)];
    }
    CGPoint baseOrigin = CGPointMake(kInvaderSize.width / 2, 180);
    
    RACSequence *aliens = [start.rac_sequence map:^(id value){
        NSUInteger row = [value integerValue]/kInvaderColCount;
        NSUInteger col = [value integerValue]%kInvaderColCount;
        
        CGPoint invaderPosition = CGPointMake(col * (kInvaderSize.width + kInvaderGridSpacing.width) + baseOrigin.x,
                                              row * (kInvaderGridSpacing.height + kInvaderSize.height) + baseOrigin.y);
        SKColor *invaderColor = @[[SKColor redColor], [SKColor greenColor], [SKColor blueColor]][row%3];
        SKSpriteNode* invader = [SKSpriteNode spriteNodeWithColor:invaderColor size:kInvaderSize];
        invader.name = kInvaderName;
        invader.position = invaderPosition;
        [self addChild:invader];
        
        return invader;
    }];
    
    [aliens all:^BOOL(id value) {
        return YES;
    }];
}