/**
 * 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.accumulators;

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.Serializable;

/**
 * An implementation of an accumulator capable of counting occurences
 *
 * @author etirelli
 *
 */
public class CountAccumulateFunction implements AccumulateFunction {

    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {

    }

    public void writeExternal(ObjectOutput out) throws IOException {

    }

    protected static class CountData implements Externalizable {
        public long   count = 0;

        public CountData() {}
        
        public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
            count   = in.readLong();
        }

        public void writeExternal(ObjectOutput out) throws IOException {
            out.writeLong(count);
        }

    }

    /* (non-Javadoc)
     * @see org.drools.base.accumulators.AccumulateFunction#createContext()
     */
    public Serializable createContext() {
        return new CountData();
    }

    /* (non-Javadoc)
     * @see org.drools.base.accumulators.AccumulateFunction#init(java.lang.Object)
     */
    public void init(Serializable context) throws Exception {
        CountData data = (CountData) context;
        data.count = 0;
    }

    /* (non-Javadoc)
     * @see org.drools.base.accumulators.AccumulateFunction#accumulate(java.lang.Object, java.lang.Object)
     */
    public void accumulate(Serializable context,
                           Object value) {
        CountData data = (CountData) context;
        data.count++;
    }

    /* (non-Javadoc)
     * @see org.drools.base.accumulators.AccumulateFunction#reverse(java.lang.Object, java.lang.Object)
     */
    public void reverse(Serializable context,
                        Object value) throws Exception {
        CountData data = (CountData) context;
        data.count--;
    }

    /* (non-Javadoc)
     * @see org.drools.base.accumulators.AccumulateFunction#getResult(java.lang.Object)
     */
    public Object getResult(Serializable context) throws Exception {
        CountData data = (CountData) context;
        return new Long( data.count );
    }

    /* (non-Javadoc)
     * @see org.drools.base.accumulators.AccumulateFunction#supportsReverse()
     */
    public boolean supportsReverse() {
        return true;
    }

}