function [signal_filtered, Z, P] = iirFilter(N, cutoffFreq, signal, samplingFreq, filterType)
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% function [signal_filtered, Z, P] = iirFilter(N, cutoffFreq, signal, samplingFreq, filterType)
% ex.: [signal_filtered, Z, P] = iirFilter(6, [5 20], x, 200, 1)
%
% Task:
%   To create and apply an IIR filter (Butterworth or Chebyshev)
%   Supports low-pass or band-pass depending on the cutoffFreq input.
%
% Inputs:
%   -N: order of the filter
%   -cutoffFreq: scalar (for low-pass) or 2-element vector [low high] for bandpass
%   -signal: input signal to be filtered
%   -samplingFreq: sampling frequency in Hz
%   -filterType: 1 = Butterworth, 2 = Chebyshev type I
%
% Outputs:
%   -signal_filtered: filtered signal
%   -Z: filter zeros
%   -P: filter poles
%
% Author: Tikea TE
% Date: 16/04/2025
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Design the filter
if filterType == 1
    if length(cutoffFreq) == 1
        [b, a] = butter(N, cutoffFreq / (samplingFreq / 2), 'low');
    elseif length(cutoffFreq) == 2
        [b, a] = butter(N, cutoffFreq / (samplingFreq / 2), 'bandpass');
    else
        error('cutoffFreq must be scalar or 2-element vector');
    end
elseif filterType == 2
    Rp = 10; % ripple for Chebyshev filter
    if length(cutoffFreq) == 1
        [b, a] = cheby1(N, Rp, cutoffFreq / (samplingFreq / 2), 'low');
    elseif length(cutoffFreq) == 2
        [b, a] = cheby1(N, Rp, cutoffFreq / (samplingFreq / 2), 'bandpass');
    else
        error('cutoffFreq must be scalar or 2-element vector');
    end
else
    error('Filter type must be 1 (Butterworth) or 2 (Chebyshev)');
end

% Analyze zeros/poles
[Z, P] = zeroPole(a, b, 1);

% Show frequency response
figure;
freqz(b, a, N, samplingFreq);
title('Frequency response');
grid on;

% Apply filter to signal
signal_filtered = filter(b, a, signal);

end