How can I change irregular wave into Fourier series

Question

I made irregular wave consisting of 16 regular waves with random phase difference. In addition, I tried to divide the irregular wave to several waves which are forms of fourier series. So I made the code below line 11. But when I ran this code, I couldn't get the result even after 20 minutes. Taking a long time to get the result also worries me, but the bigger problem is that I'm not sure whether the result is correct or not. How can I convert 'irregular wave' to 'fourier series'?

 function regular
 t = (0 : 0.01 : 300); %% time
 w = (0.25:0.05:1);   %% wave frequency
 A = [0 0.14 0.45 0.8 0.95 0.95 0.88 0.77 0.67 0.6 0.53 0.45 0.4 0.36 0.32 0.28]; %% wave amplitude

  phase1 = 2*pi*rand(1,length(w));   %% phase difference
   for ii = 1:length(w)
     for jj = 1:length(t)       
     elev(ii,jj) = (A(ii)*cos(-w(ii)*t(jj)+phase1(ii))); %% wave elevation 
   end
 end
syms t
 T0 = 125;
 w0 = 2*pi/T0;
 a0 = (2/T0)*int(sum(elev),t,-T0/2,T0/2);


 for k = 1:5
     a(k)=(2/T0)*int(sum(elev)*cos(k*w0*t),t,-T0/2,T0/2);
     b(k)=(2/T0)*int(sum(elev)*sin(k*w0*t),t,-T0/2,T0/2);
     F1(k) = a(k)*cos(k*w0*t)+b(k)*sin(k*w0*t);
 end
figure;
plot(t,a0/2+sum(F1));
end