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Utility classes developed at Adrian Smith Software (A.S.S.)
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package com.databasesandlife.util.wicket;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

import org.apache.wicket.AttributeModifier;
import org.apache.wicket.extensions.markup.html.form.select.IOptionRenderer;
import org.apache.wicket.extensions.markup.html.form.select.Select;
import org.apache.wicket.extensions.markup.html.form.select.SelectOptions;
import org.apache.wicket.markup.ComponentTag;
import org.apache.wicket.markup.html.WebMarkupContainer;
import org.apache.wicket.markup.html.form.FormComponentPanel;
import org.apache.wicket.markup.html.list.ListItem;
import org.apache.wicket.markup.html.list.ListView;
import org.apache.wicket.model.IModel;
import org.apache.wicket.model.PropertyModel;

/**
 * Drop-down where options are in groups; user may select only one element or multiple elements.
 * @param  The object type to be selected
 *
 * @author This source is copyright Adrian Smith and licensed under the LGPL 3.
 * @see Project on GitHub
 */
public class GroupedDropDownChoice extends FormComponentPanel> {

    public static class DropDownChoiceGroup implements Serializable {
        private List values;
        private String groupName;
        public DropDownChoiceGroup(String groupName,List values) { this.values = values; this.groupName = groupName; }
        public DropDownChoiceGroup(String groupName) { this(groupName, new ArrayList()); }
        public List getValues(){ return values; }
        public String getGroupName(){ return groupName; }
        public void add(T item) { values.add(item); }
    }

    /** Used by wicket */ 
    protected List selectModel = new ArrayList<>();
    private Select> select;
    
    protected void init(IModel> model, List> values, final IOptionRenderer renderer, String htmlId) {
        setModel(model);
        select = new Select>("select",new PropertyModel>(this,"selectModel"));
        if(!htmlId.isEmpty()) select.add(new AttributeModifier("id", htmlId));
        if(isMultiple()) select.add(new AttributeModifier("multiple","multiple"));
        add(select);
        var groups = new ListView>("groups",values) {
            @Override
            protected void populateItem(ListItem> arg0) {
                var g = arg0.getModelObject();
                var optgroup = new WebMarkupContainer("optgroup");
                optgroup.add(new AttributeModifier("label",g.getGroupName()));
                //for the sake of customization a list view with SelectOption objects
                //can be replaced with:
                 optgroup.add(new SelectOptions("select-options", new PropertyModel>(g,"values"), renderer));
//              optgroup.add(new ListView("select-options",g.getValues()){
//
//                  @Override
//                  protected void populateItem(ListItem item) {
//                      T value = item.getModelObject();
//                      SelectOption opt = new SelectOption("select-option", Model.of(value));
//                      opt.add(new Label("option-text",renderer.getDisplayValue(value)));
//                      item.add(opt);
//                  }
//                  
//              });
                arg0.add(optgroup);
            }
        };  
        select.add(groups);
    }
    
    protected GroupedDropDownChoice(String wicketId) {
        super(wicketId);
    }
    
    /**
     * @param model allow multiple selections, unless model is a {@link SingleEntryModelAdaptor}.
     */
    public GroupedDropDownChoice(
        String wicketId, IModel> model, List> values, final IOptionRenderer renderer, String htmlId
    ){
        super(wicketId);
        init(model, values, renderer, htmlId);
    }
    
    public boolean isMultiple() {
        return ! (getModel() instanceof SingleEntryModelAdaptor);
    }
    
    @Override protected void onComponentTag(ComponentTag tag) {
        super.onComponentTag(tag);
        tag.setName("span");  // So that clients can write  etc.
    }
    
    @Override
    public void convertInput(){
        setConvertedInput(select.getConvertedInput());
    }
    
    @Override
    protected void onBeforeRender(){
        selectModel = getModelObject(); //to pre-select the passed value
        
        // Select object tries to determine if it should set a List or just an X, by inspecting the current model.
        // If it's a Collection it sets List otherwise X. But if it's null, it doesn't know, so just sets X.
        // But our model is always List so we get a ClassCastException if Select gives us an X.
        // We could just say "if (null) { model=new List(); }" but that is unclean; what meaning does it have, if you
        // want to select a list of things, for that list to be null? The correct value is, if nothing is selected, the empty list.
        if (selectModel == null) throw new NullPointerException("model is null; use empty list instead");
        
        super.onBeforeRender();
    }
}