/*
 * Copyright 2016 Red Hat, Inc. and/or its affiliates.
 *
 * Licensed 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.kie.dmn.feel.runtime.functions;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import org.kie.dmn.api.feel.runtime.events.FEELEvent;
import org.kie.dmn.api.feel.runtime.events.FEELEvent.Severity;
import org.kie.dmn.feel.runtime.events.InvalidParametersEvent;
import org.kie.dmn.feel.runtime.functions.FEELFnResult;

public class UnionFunction
        extends BaseFEELFunction {

    public UnionFunction() {
        super( "union" );
    }

    public FEELFnResult<List> invoke(@ParameterName("list") Object[] lists) {
        if ( lists == null ) {
            return FEELFnResult.ofError(new InvalidParametersEvent(Severity.ERROR, "lists", "cannot be null"));
        }
        // spec requires us to return a new list
        List result = new ArrayList();
        for ( Object list : lists ) {
            if ( list instanceof Collection ) {
                ((Collection) list).stream().forEach( i -> {
                    if ( !result.contains( i ) ) result.add( i );
                } );
            } else if ( list != null ) {
                // singleton list
                if ( !result.contains( list ) ) result.add( list );
            } else {
                // TODO review accordingly to spec, original behavior was: return null;
                return FEELFnResult.ofError(new InvalidParametersEvent(Severity.ERROR, "lists", "one of the elements in list is null"));
            }
        }
        return FEELFnResult.ofResult( result );
    }
}