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Utility classes developed at Adrian Smith Software (A.S.S.)

There is a newer version: 21.0.1

package com.databasesandlife.util.wicket;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Objects;

import org.apache.wicket.model.IModel;

import javax.annotation.CheckForNull;
import javax.annotation.Nonnull;

/**
 * Wraps an underlying model, and exposes the empty list if the underlying model has a particular value.
 * That particular value of the underlying model may be null.
 *
 * @author This source is copyright Adrian Smith and licensed under the LGPL 3.
 * @see Project on GitHub
 */
@SuppressWarnings("serial")
public class EmptyListIsSpecialWrapperModel implements IModel> {
    protected @CheckForNull List specialValueInUnderlyingModel;
    protected @Nonnull IModel> underlyingModel;
    
    /** @param specialValue which values to be saved in the underlying model, in the case the user doesn't enter anything */
    public EmptyListIsSpecialWrapperModel(@CheckForNull List specialValue, @Nonnull IModel> model) { 
        specialValueInUnderlyingModel = specialValue;
        underlyingModel = model; 
    }
    
    @Override public void detach() { }

    /**
     * Takes data from Wicket and applies it to the underlying model.
     * Checks to see if the data from Wicket is empty and, if so, sets the underlying model with the special value.
     */
    @Override public void setObject(List userData) { 
        underlyingModel.setObject(userData.isEmpty() ? specialValueInUnderlyingModel : userData); 
    }

    /**
     * Takes data from the underlying model, and passes it to Wicket.
     * If the underlying model contains the special value, then pass the empty list to Wicket.
     * Otherwise, simply pass the underlying model on to Wicket.
     * The exception being that if the underlying model is null, we return the empty list, that makes more sense for Wicket.
     */
    @Override public @Nonnull List getObject() {
        var underlyingValue = underlyingModel.getObject();
        
        var underlyingSet = underlyingValue == null ? null : new HashSet<>(underlyingValue);
        var specialValueSet = specialValueInUnderlyingModel == null ? null : new HashSet<>(specialValueInUnderlyingModel);
        
        if (Objects.equals(underlyingSet, specialValueSet)) return new ArrayList<>();
        else if (underlyingValue == null) return new ArrayList<>();
        else return underlyingValue;
    }
}