Shifting Phase Using FFT

So I have a simple program where I want to shift a simple sine function pi/2. Now I knwo this would be extremely easy by just inserting a bias (i.e. A*sin(2*pi*frequency + bias). But this program is a simple way to test a theory. I need to shift complicated magnetic data, but the shift is frequency dependent. So to figure out how to do that I just want to shift this sin wave by a set shift, but I want to do it in the frequency domain. Code is below. Thank you!

clear all

time = 1:0.01:2*pi; %Create time vector
mag = sin(2*pi*time);

Y = fft(mag); %transform
Pnewr = pi/2;
%t = angle(mag);
t = imag(Y);
%t_fin = t-Pnewr; %Subtract the pahse delay from the original phase vector

R=real(Y);
I=t;
k = I./R

Phi = tan(k);

PhiFinal = Phi-Pnewr;
PhiFinal = PhiFinal'
IFinal = R * atan(PhiFinal);

spec=complex(R,IFinal);
Finalspec = ifft(spec); %Invert the transform
Final = Finalspec;

plot(time,mag);
hold on
plot(time,Final,'r')
grid on

[Matt J]

Your code gives me no error messages. What's your question?