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The main module contains the GeoTools public interfaces that are used by other GeoTools modules (and GeoTools applications). Where possible we make use industry standard terms as provided by OGC and ISO standards. The formal GeoTools public api consists of gt-metadata, jts and the gt-main module. The main module contains the default implementations that are available provided to other GeoTools modules using our factory system. Factories are obtained from an appropriate FactoryFinder, giving applications a chance configure the factory used using the Factory Hints facilities. FilterFactory ff = CommonFactoryFinder.getFilterFactory(); Expression expr = ff.add( expression1, expression2 ); If you find yourself using implementation specific classes chances are you doing it wrong: Expression expr = new AddImpl( expression1, expressiom2 );

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/*
 *    GeoTools - The Open Source Java GIS Toolkit
 *    http://geotools.org
 *
 *    (C) 2005-2008, Open Source Geospatial Foundation (OSGeo)
 *
 *    This library is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU Lesser General Public
 *    License as published by the Free Software Foundation;
 *    version 2.1 of the License.
 *
 *    This library 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
 *    Lesser General Public License for more details.
 */
package org.geotools.feature.visitor;

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import org.geotools.data.simple.SimpleFeatureCollection;
import org.geotools.factory.CommonFactoryFinder;
import org.geotools.filter.IllegalFilterException;
import org.opengis.feature.simple.SimpleFeature;
import org.opengis.feature.simple.SimpleFeatureType;
import org.opengis.filter.FilterFactory;
import org.opengis.filter.expression.Expression;

/**
 * Calculates the minimum value of an attribute.
 *
 * @author Cory Horner, Refractions
 * @since 2.2.M2
 */
public class MinVisitor implements FeatureCalc, FeatureAttributeVisitor {
    private Expression expr;
    Comparable minvalue;
    Comparable curvalue;
    boolean visited = false;

    public MinVisitor(String attributeTypeName) {
        FilterFactory factory = CommonFactoryFinder.getFilterFactory(null);
        expr = factory.property(attributeTypeName);
    }

    public MinVisitor(int attributeTypeIndex, SimpleFeatureType type)
            throws IllegalFilterException {
        FilterFactory factory = CommonFactoryFinder.getFilterFactory(null);
        expr = factory.property(type.getDescriptor(attributeTypeIndex).getLocalName());
    }

    public MinVisitor(String attrName, SimpleFeatureType type) throws IllegalFilterException {
        FilterFactory factory = CommonFactoryFinder.getFilterFactory(null);
        expr = factory.property(type.getDescriptor(attrName).getLocalName());
    }

    public MinVisitor(Expression expr) throws IllegalFilterException {
        this.expr = expr;
    }

    public void init(SimpleFeatureCollection collection) {
        // do nothing
    }

    @Override
    public List getExpressions() {
        return Arrays.asList(expr);
    }

    @Override
    public Optional> getResultType(List inputTypes) {
        return CalcUtil.reflectInputTypes(1, inputTypes);
    }

    /**
     * Visitor function, which looks at each feature and finds the minimum.
     *
     * @param feature the feature to be visited
     */
    public void visit(SimpleFeature feature) {
        visit((org.opengis.feature.Feature) feature);
    }

    public void visit(org.opengis.feature.Feature feature) {
        Object attribValue = expr.evaluate(feature);

        if (attribValue == null) {
            return; // attribute is null, therefore skip
        }

        curvalue = (Comparable) attribValue;
        if ((!visited) || (curvalue.compareTo(minvalue) < 0)) {
            minvalue = curvalue;
            visited = true;
        }
    }

    /**
     * Get the min value.
     *
     * @return Minimum value
     */
    public Comparable getMin() {
        /** Return the minimum value derived from the collection */
        if (!visited) {
            throw new IllegalStateException("Must visit before min value is ready!");
        }

        return minvalue;
    }

    public void reset() {
        /** Reset the count and current minimum */
        this.visited = false;
        this.minvalue = Integer.valueOf(0);
    }

    public CalcResult getResult() {
        if (!visited) {
            return CalcResult.NULL_RESULT;
        }

        return new MinResult(minvalue);
    }

    public Expression getExpression() {
        return expr;
    }

    /**
     * Overwrites the result stored by the visitor. This should only be used by optimizations which
     * will tell the visitor the answer rather than visiting all features.
     *
     * For 'min', the value stored is of type 'Comparable'.
     */
    public void setValue(Object result) {
        visited = true;
        minvalue = (Comparable) result;
    }

    public static class MinResult extends AbstractCalcResult {
        private Comparable minValue;

        public MinResult(Comparable newMinValue) {
            minValue = newMinValue;
        }

        public Object getValue() {
            Comparable min = (Comparable) minValue;

            return min;
        }

        public boolean isCompatible(CalcResult targetResults) {
            // list each calculation result which can merge with this type of result
            if (targetResults instanceof MinResult || targetResults == CalcResult.NULL_RESULT) {
                return true;
            }

            return false;
        }

        public CalcResult merge(CalcResult resultsToAdd) {
            if (!isCompatible(resultsToAdd)) {
                throw new IllegalArgumentException("Parameter is not a compatible type");
            }

            if (resultsToAdd == CalcResult.NULL_RESULT) {
                return this;
            }

            if (resultsToAdd instanceof MinResult) {
                // take the smaller of the 2 values
                Comparable toAdd = (Comparable) resultsToAdd.getValue();
                Comparable newMin = minValue;

                if (newMin.getClass()
                        != toAdd.getClass()) { // 2 different data types, therefore convert
                    Class bestClass = CalcUtil.bestClass(new Object[] {toAdd, newMin});
                    if (bestClass != toAdd.getClass())
                        toAdd = (Comparable) CalcUtil.convert(toAdd, bestClass);
                    if (bestClass != newMin.getClass())
                        newMin = (Comparable) CalcUtil.convert(newMin, bestClass);
                }
                if (newMin.compareTo(toAdd) > 0) {
                    newMin = toAdd;
                }

                return new MinResult(newMin);
            } else {
                throw new IllegalArgumentException(
                        "The CalcResults claim to be compatible, but the appropriate merge method has not been implemented.");
            }
        }
    }
}