function [ target_list_RDA ] = angle_estimation(target_list_RDA_temp, echo_mtx, A, d, lambda, acc)
% This function estimates all targets angle
%
% Usage: 
% [target_list_RDA] = angle_estimation(target_list_RDA_temp, echo_mtx, A, d, lambda, acc)
%
% Inputs:
%   target_list_RDA_temp:   Temporary list of targets before angle estimation
%   echo_mtx:               Original echo data matrix
%   A:                      Chirp measurement matrix
%   d:                      Antenna spacing
%   lambda:                 Wave length
%   acc:                    Accuracy for angle estimation
%
% Outputs:
%   target_list_RDA:        Target list include range, doppler and angle information


    % parameters
    if nargin < 6
        acc = 181;
    end
    
    % calculate all targets angle
    target_list_RDA = zeros(size(target_list_RDA_temp));
    for i = 1: size(target_list_RDA_temp, 1)
        t_rda = target_list_RDA_temp(i, :);
        target_list_RDA(i, 1:2) = t_rda(1:2);
        target_list_RDA(i, 3) = cal_angle(t_rda(1), t_rda(2), echo_mtx, A, d, lambda, acc);
    end

end


%% sub-functions
% calculate target actual angle with range and doppler index
function [ angle ] = cal_angle(r_idx, d_idx, echo_mtx, A, d, lambda, acc)

    % range doppler processing
    echo_r = zeros([size(echo_mtx, 1), 1, size(echo_mtx, 3)]);
    for i = 1 : size(echo_mtx, 3)
        echo_r(:, 1, i) = sum(bsxfun(@times, echo_mtx(:, :, i), A(:, r_idx)'), 2);
    end
    echo_r = squeeze(echo_r);
    echo_r_ex = [echo_r, zeros(size(echo_r))];
    echo_rd = zeros(size(echo_r_ex, 1), 1);
    for i = 1 : size(echo_r_ex, 1)
         temp_v = fftshift(fft(echo_r_ex(i,:)));
         echo_rd(i) = temp_v(d_idx);
    end
    
    % CBF
    THETA = linspace(-90, 90, round(acc));
    fai = exp((0: size(echo_r_ex, 1) - 1)' *...
        -1j * 2 * pi / lambda * d * sin(THETA / 180 * pi));
    angle_mf = abs(fai'* echo_rd);
    [v, idx] = max(angle_mf);
    angle = THETA(idx);

end