Limits Continuity And Differentiability

Let $[t]$ denote the greatest integer less than or equal to $t$. If the function

$$ f(x)=\left\{\begin{array}{cl} b^2 \sin \left(\frac{\pi}{2}\left[\frac{\pi}{2}(\cos x+\sin x) \cos x\right]\right), & x<0 \\ \frac{\sin x-\frac{1}{2} \sin 2 x}{x^3} & , x>0 \\ a & , x=0 \end{array}\right. $$

is continuous at $x=0$, then $a^2+b^2$ is equal to :