/**
 * Copyright 2010 JBoss Inc
 *
 * 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.drools.base.extractors;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import org.drools.base.AccessorKey;
import org.drools.base.ValueType;
import org.drools.base.ClassFieldAccessorCache.CacheEntry;
import org.drools.common.InternalWorkingMemory;
import org.drools.spi.InternalReadAccessor;
import org.mvel2.MVEL;
import org.mvel2.compiler.CompiledExpression;
import org.mvel2.compiler.ExpressionCompiler;

/**
 * A class field extractor that uses MVEL engine to extract the actual value for a given
 * expression. We use MVEL to resolve nested accessor expressions.
 *
 * @author etirelli
 */
public class MVELClassFieldReader extends BaseObjectClassFieldReader {

    private static final long  serialVersionUID = 510l;

    private CompiledExpression mvelExpression   = null;
    private Map                extractors       = null;

    public MVELClassFieldReader() {
    }

    public MVELClassFieldReader(Class cls,
                                String fieldName,
                                CacheEntry cache) {
        super( -1, // index
               Object.class, // fieldType
               ValueType.determineValueType( Object.class ) ); // value type
        this.extractors = new HashMap();

        ExpressionCompiler compiler = new ExpressionCompiler( fieldName );
        this.mvelExpression = compiler.compile();

        Set inputs = compiler.getParserContextState().getInputs().keySet();
        for ( Iterator it = inputs.iterator(); it.hasNext(); ) {
            String basefield = (String) it.next();
            if ( "this".equals( basefield ) ) {
                continue;
            }
            InternalReadAccessor extr = cache.getReadAccessor( new AccessorKey( cls.getName(),
                                                                                basefield,
                                                                                AccessorKey.AccessorType.FieldAccessor ),
                                                               cls );
            this.extractors.put( basefield,
                                 extr );
        }
    }

    //    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
    //        super.readExternal(in);
    //        mvelExpression  = (CompiledExpression)in.readObject();
    //        extractors  = (Map)in.readObject();
    //    }
    //
    //    public void writeExternal(ObjectOutput out) throws IOException {
    //        super.writeExternal(out);
    //        out.writeObject(mvelExpression);
    //        out.writeObject(extractors);
    //    }

    /* (non-Javadoc)
     * @see org.drools.base.extractors.BaseObjectClassFieldExtractor#getValue(java.lang.Object)
     */
    public Object getValue(InternalWorkingMemory workingMemory,
                           Object object) {
        Map variables = new HashMap();
        for ( Iterator it = this.extractors.entrySet().iterator(); it.hasNext(); ) {
            Map.Entry entry = (Map.Entry) it.next();
            String var = (String) entry.getKey();
            InternalReadAccessor extr = (InternalReadAccessor) entry.getValue();

            variables.put( var,
                           extr.getValue( workingMemory,
                                          object ) );
        }
        return MVEL.executeExpression( mvelExpression,
                                       object,
                                       variables );
    }

}