/*
 * *****************************************************************************
 * Copyright (C) 2014-2022 Dennis Sheirer
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 * ****************************************************************************
 */

package io.github.dsheirer.buffer;

import java.nio.ByteBuffer;

/**
 * Implements a factory for creating SignedByteNativeBuffer instances
 */
public class SignedByteNativeBufferFactory implements INativeBufferFactory
{
    private static final float DC_FILTER_GAIN = 0.02f; //Normalizes DC over period of ~50 (1 / .02) buffers
    private float mIAverageDc = 0.0f;
    private float mQAverageDc = 0.0f;

    @Override
    public INativeBuffer getBuffer(ByteBuffer samples, long timestamp)
    {
        byte[] copy = new byte[samples.capacity()];
        samples.get(copy);
        calculateDc(copy);
        return new SignedByteNativeBuffer(copy, timestamp, mIAverageDc, mQAverageDc);
    }

    /**
     * Calculates the average DC in the sample stream so that it can be subtracted from the samples when the
     * native buffer is used.
     * @param samples containing DC offset
     */
    private void calculateDc(byte[] samples)
    {
        double iDcAccumulator = 0;
        double qDcAccumulator = 0;

        for(int x = 0; x < samples.length; x += 2)
        {
            iDcAccumulator += samples[x];
            qDcAccumulator += samples[x + 1];
        }

        iDcAccumulator /= (samples.length / 2);
        iDcAccumulator /= 128.0f;
        iDcAccumulator -= mIAverageDc;
        mIAverageDc += (iDcAccumulator * DC_FILTER_GAIN);

        qDcAccumulator /= (samples.length / 2);
        qDcAccumulator /= 128.0f;
        qDcAccumulator -= mQAverageDc;
        mQAverageDc += (qDcAccumulator * DC_FILTER_GAIN);
    }
}