function signal_filtered = firFilter(N, cutoffFreq, signal, samplingFreq)
%{
function signal_filtered = firFilter(N, cutoffFreq, signal, samplingFreq)
Ex: signal_filtered = firFilter(30, [5 20], x, 200)

Task: Apply an FIR bandpass filter to a signal.

Inputs:
    - N: filter order
    - cutoffFreq: 2-element vector [low high] for bandpass cutoff (Hz)
    - signal: input signal to be filtered
    - samplingFreq: sampling frequency (Hz)

Output:
    - signal_filtered: the filtered output signal

Author: Tikea TE
Date: 16/04/2025
%}

% Normalize the cutoff frequency
Wn = cutoffFreq / (samplingFreq / 2);  % Normalize to Nyquist

% Design the FIR bandpass filter using Hamming window
b = fir1(N, Wn, 'bandpass', hamming(N+1));
a = 1;  % FIR filter has only numerator

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

% Plot frequency response
figure;
freqz(b, a, 1024, samplingFreq);
title('Frequency Response of FIR Filter');
grid on;

% Plot impulse response
figure;
impz(b, a);
title('Impulse Response of FIR Filter');
xlabel('Samples (n)');
ylabel('Amplitude');
grid on;

end