%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Diese Funktion bestimmt die aufgrund der Korrektur mit der Leermessung
% auftretende Verschiebung der HRIRs in negative Richtung und korri-
% giert diese. Die Fensterlänge kann dabei beliebig gewählt werden. Der 
% Parameter "smooth" gibt an , ob die HRIRs geglättet werden sollen 
% (smooth = 1) oder nicht (smooth = 0). Das Programm orientiert sich an 
% dem paper von Keller, Hartung, Takahashi aus dem Jahr 1998.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


function [hrirshift_l, hrirshift_r, az_num, el_num] = offset(hrir_l, hrir_r, fensterzeit, smooth)
% Fensterzeit in ms zwischen 0 und 500
fensterlaenge = fensterzeit * 100; 

L = size(hrir_l,3);
zeilen = size(hrir_l,1);
spalten = size(hrir_l,2);
fenster = zeros(1,L);
fenster(1) = 1;
fenster(L-(fensterlaenge-2):L) = 1;

hrirsmooth_l = zeros(zeilen,spalten,L);
hrirsmooth_r = zeros(zeilen,spalten,L);
offset_l = zeros(zeilen,spalten);
offset_r = zeros(zeilen,spalten);

for i = 1:zeilen
    for j = 1:spalten
        HRIR_l = squeeze(hrir_l(i,j,:)).';
        HRIR_r = squeeze(hrir_r(i,j,:)).';
        faltung_l = cconv(HRIR_l.^2, fenster,L);
        faltung_r = cconv(HRIR_r.^2, fenster,L);
        offset_l(i,j) = find(faltung_l == max(faltung_l),1);
        offset_r(i,j) = find(faltung_r == max(faltung_r),1);
        filter_l = zeros(1,L);
        filter_r = zeros(1,L);
        if offset_l(i,j)+fensterlaenge-1 <= L
            filter_l(1,offset_l(i,j):offset_l(i,j)+fensterlaenge-1) = 1;
        else
            filter_l(1,offset_l(i,j):L) = 1;
            filter_l(1,1:fensterlaenge-L+offset_l(i,j)-1) = 1;
        end
        if offset_r(i,j)+fensterlaenge-1 <= L
            filter_r(1,offset_r(i,j):offset_r(i,j)+fensterlaenge-1) = 1;
        else
            filter_r(1,offset_r(i,j):L) = 1;
            filter_r(1,1:fensterlaenge-L+offset_r(i,j)-1) = 1;
        end
        hrirsmooth_l(i,j,:) = HRIR_l .* filter_l;
        hrirsmooth_r(i,j,:) = HRIR_r .* filter_r;
    end
end

offset_l(offset_l < L/2) = nan;
offset_r(offset_r < L/2) = nan;

[off_l, I_l] = min(offset_l(:));
[off_r, I_r] = min(offset_r(:));

if off_l <= off_r
    offset = off_l;
    I = I_l;
else 
    offset = off_r;
    I = I_r;
end

if isnan(offset) == 1
    az_num = 0;
    el_num = 0;
    if smooth == 0
    hrirshift_l = hrir_l;
    hrirshift_r = hrir_r;
    else
    hrirshift_l = hrirsmooth_l;
    hrirshift_r = hrirsmooth_r;
    end
else
    [az_num, el_num] = ind2sub(size(offset_l), I);

    if smooth == 0
        hrirshift_l = circshift(hrir_l, [0,0,(L-offset)+1]);
        hrirshift_r = circshift(hrir_r, [0,0,(L-offset)+1]);
    else
        hrirshift_l = circshift(hrirsmooth_l, [0,0,(L-offset)+1]);
        hrirshift_r = circshift(hrirsmooth_r, [0,0,(L-offset)+1]);
    end
end

end