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 * #%L
 * Image processing operations for SciJava Ops.
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 *    this list of conditions and the following disclaimer.
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package org.scijava.ops.image.threshold.ij1;

import org.scijava.ops.image.threshold.AbstractComputeThresholdHistogram;
import net.imglib2.histogram.Histogram1d;
import net.imglib2.type.numeric.RealType;

// NB - this plugin adapted from Gabriel Landini's code of his AutoThreshold
// plugin found in Fiji (version 1.14). The method was ported from IJ1 by
// Gabriel and somewhat enhanced ("re-implemented so we can ignore black/white
// and set the bright or dark objects")

/**
 * Implements the default threshold method from ImageJ.
 *
 * @author Barry DeZonia
 * @author Gabriel Landini
 * @implNote op names='threshold.ij1', priority='100.'
 */
public class ComputeIJ1Threshold<T extends RealType<T>> extends
	AbstractComputeThresholdHistogram<T>
{

	/**
	 * TODO
	 *
	 * @param hist the {@link Histogram1d}
	 * @return the IJ1 threshold value
	 */
	@Override
	public long computeBin(final Histogram1d<T> hist) {
		final var histogram = hist.toLongArray();
		return computeBin(histogram);
	}

	/**
	 * Original IJ implementation for compatibility.
	 */
	public static long computeBin(final long[] histogram) {
		int level;
		final var maxValue = histogram.length - 1;
		double result, sum1, sum2, sum3, sum4;

        var min = 0;
		while (histogram[min] == 0 && min < maxValue)
			min++;
        var max = maxValue;
		while (histogram[max] == 0 && max > 0)
			max--;
		if (min >= max) {
			level = histogram.length / 2;
			return level;
		}

        var movingIndex = min;
		do {
			sum1 = sum2 = sum3 = sum4 = 0.0;
			for (var i = min; i <= movingIndex; i++) {
				sum1 += i * histogram[i];
				sum2 += histogram[i];
			}
			for (var i = movingIndex + 1; i <= max; i++) {
				sum3 += i * histogram[i];
				sum4 += histogram[i];
			}
			result = (sum1 / sum2 + sum3 / sum4) / 2.0;
			movingIndex++;
		}
		while (movingIndex + 1 <= result && movingIndex < max - 1);

		level = (int) Math.round(result);
		return level;
	}

}
