package org.signalml.domain.signal.filter.fft;

import org.apache.commons.math.complex.Complex;
import org.signalml.domain.montage.filter.FFTSampleFilter;
import org.signalml.domain.montage.filter.SampleFilterDefinition;
import org.signalml.domain.signal.filter.SinglechannelSampleFilterEngine;
import org.signalml.domain.signal.samplesource.SampleSource;
import org.signalml.math.fft.FourierTransform;

/**
 * This engine can be used to filter very long signals in order to export them to a file.
 * It uses the overlap-add to filter the data.
 *
 * @author Piotr Szachewicz
 */
public class FFTFilterEngineForExport extends SinglechannelSampleFilterEngine {

	/**
	 * The sample filter used to filter the data.
	 */
	private FFTSampleFilter fftSampleFilter;
	/**
	 * Buffer to store the overlapping part of the previously filtered sequence.
	 * See {@link http://en.wikipedia.org/wiki/Overlap%E2%80%93add_method#The_algorithm}
	 * for reference.
	 */
	private double[] overlapBuffer;

	public FFTFilterEngineForExport(SampleSource source, FFTSampleFilter filter) {
		super(source);
		this.fftSampleFilter = filter;
	}

	@Override
	public void getSamples(double[] target, int signalOffset, int count, int arrayOffset) {

		double[] samples = new double[count];
		source.getSamples(samples, signalOffset, count, 0);

		FourierTransform fourierTransform = new FourierTransform(fftSampleFilter.getWindowType(), fftSampleFilter.getWindowParameter());
		Complex[] samplesFFT = fourierTransform.forwardFFT(samples);
		FFTSinglechannelSampleFilter.multiplyFFTByFFTSampleFilter(samplesFFT, fftSampleFilter, source.getSamplingFrequency());
		double[] filteredSignal = fourierTransform.inverseFFT(samplesFFT);

		if (overlapBuffer != null) {
			for (int i = 0; i < overlapBuffer.length; i++) {
				filteredSignal[i] += overlapBuffer[i];
			}
		}
		System.arraycopy(filteredSignal, 0, target, 0, count);

		overlapBuffer = new double[filteredSignal.length - count];
		System.arraycopy(filteredSignal, count, overlapBuffer, 0, overlapBuffer.length);
	}

	@Override
	public SampleFilterDefinition getFilterDefinition() {
		return fftSampleFilter;
	}

}