/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.sis.coverage;

import java.util.HashSet;
import java.util.function.DoubleToIntFunction;
import org.apache.sis.math.MathFunctions;
import org.apache.sis.feature.internal.Resources;


/**
 * Keep trace of allocated {@link Float#NaN} ordinal values for avoiding range collisions when building categories.
 * This is a temporary object used only at {@link SampleDimension} construction time for producing values suitable
 * to {@link MathFunctions#toNanFloat(int)}. Instances of this class are given for {@code toNaN} argument in the
 * {@link Category} constructor.
 *
 * @author  Martin Desruisseaux (Geomatys)
 */
@SuppressWarnings({"serial", "CloneableImplementsClone"})                       // Not intended to be serialized.
final class ToNaN extends HashSet<Integer> implements DoubleToIntFunction {
    /**
     * The value which should be assigned ordinal 0 if that ordinal value is available.
     * For performance reason, the background value should be assigned ordinal 0 when possible.
     * This is {@code null} if unspecified.
     */
    Number background;

    /**
     * To be constructed only from this package.
     */
    ToNaN() {
    }

    /**
     * Sets this function to the same state than after construction.
     * This method is invoked when the same builder is reused for creating many sample dimensions.
     */
    @Override
    public void clear() {
        super.clear();
        background = null;
    }

    /**
     * Returns {@code true} if the specified value is the background value.
     */
    private boolean isBackground(final double value) {
        return (background != null) && (value == background.doubleValue());
    }

    /**
     * Mapping from sample values to ordinal values to be supplied to {@link MathFunctions#toNanFloat(int)}.
     * That mapping shall ensure that there are no ordinal value collisions between different categories in
     * the same {@link SampleDimension}.
     *
     * @param  value  a real number in the {@link Category#range} sample value range.
     * @return a value between {@value MathFunctions#MIN_NAN_ORDINAL} and {@value MathFunctions#MAX_NAN_ORDINAL} inclusive.
     */
    @Override
    public int applyAsInt(final double value) {
        if (isBackground(value) && add(0)) {
            return 0;
        }
        /*
         * For qualitative category, we need an ordinal in the [MIN_NAN_ORDINAL … MAX_NAN_ORDINAL] range.
         * This range is quite large (a few million of values) so using the sample directly usually work.
         * If it does not work, we will use an arbitrary value in that range.
         */
        int ordinal = Math.round((float) value);
        if (ordinal > MathFunctions.MAX_NAN_ORDINAL) {
            ordinal = (MathFunctions.MAX_NAN_ORDINAL + 1) / 2;
        } else if (ordinal < MathFunctions.MIN_NAN_ORDINAL) {
            ordinal = MathFunctions.MIN_NAN_ORDINAL / 2;
        }
search: if (!add(ordinal)) {
            /*
             * Following algorithms are inefficient, but those loops should be rarely needed.
             * They are executed only if many qualitative sample values are outside the range
             * of ordinal NaN values. The range allows a few million of values.
             */
            if (ordinal >= 0) {
                do if (add(++ordinal)) break search;
                while (ordinal < MathFunctions.MAX_NAN_ORDINAL);
            } else {
                do if (add(--ordinal)) break search;
                while (ordinal > MathFunctions.MIN_NAN_ORDINAL);
            }
            throw new IllegalSampleDimensionException(Resources.format(Resources.Keys.TooManyQualitatives));
        }
        return ordinal;
    }

    /**
     * Removes the NaN value which has been reserved for a qualitative category.
     * This method does nothing if {@code converted} is not a NaN value, i.e. if
     * the category is quantitative instead of qualitative.
     *
     * @param  c  the presumed qualitative category.
     */
    void remove(final Category c) {
        final float converted = (float) c.converse.range.getMinDouble();
        if (Float.isNaN(converted) && super.remove(MathFunctions.toNanOrdinal(converted))) {
            // Use of 'c.getMinDouble()' shall be consistent with 'SampleDimension.Builder.setBackground(…)'.
            if (isBackground(c.range.getMinDouble())) {
                background = null;
            }
        }
    }
}
