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package org.apache.commons.collections.functors;

import java.io.Serializable;
import java.util.Collection;
import java.util.Iterator;

import org.apache.commons.collections.Transformer;

/**
 * Transformer implementation that chains the specified closures together.
 * 
 * @since Commons Collections 3.0
 * @version $Revision: 3330 $ $Date: 2006-03-14 09:47:58 +0100 (Di, 14 Mrz 2006) $
 *
 * @author Stephen Colebourne
 */
public class ChainedTransformer implements Transformer, Serializable {

    /** Serial version UID */
    static final long serialVersionUID = 3514945074733160196L;

    /** The transformers to call in turn */
    private final Transformer[] iTransformers;

    /**
     * Factory method that performs validation and copies the parameter array.
     * 
     * @param transformers  the transformers to chain, copied, no nulls
     * @return the <code>chained</code> transformer
     * @throws IllegalArgumentException if the transformers array is null
     * @throws IllegalArgumentException if any transformer in the array is null
     */
    public static Transformer getInstance(Transformer[] transformers) {
        FunctorUtils.validate(transformers);
        if (transformers.length == 0) {
            return NOPTransformer.INSTANCE;
        }
        transformers = FunctorUtils.copy(transformers);
        return new ChainedTransformer(transformers);
    }
    
    /**
     * Create a new Transformer that calls each transformer in turn, passing the 
     * result into the next transformer. The ordering is that of the iterator()
     * method on the collection.
     * 
     * @param transformers  a collection of transformers to chain
     * @return the <code>chained</code> transformer
     * @throws IllegalArgumentException if the transformers collection is null
     * @throws IllegalArgumentException if any transformer in the collection is null
     */
    public static Transformer getInstance(Collection transformers) {
        if (transformers == null) {
            throw new IllegalArgumentException("Transformer collection must not be null");
        }
        if (transformers.size() == 0) {
            return NOPTransformer.INSTANCE;
        }
        // convert to array like this to guarantee iterator() ordering
        Transformer[] cmds = new Transformer[transformers.size()];
        int i = 0;
        for (Iterator it = transformers.iterator(); it.hasNext();) {
            cmds[i++] = (Transformer) it.next();
        }
        FunctorUtils.validate(cmds);
        return new ChainedTransformer(cmds);
    }

    /**
     * Factory method that performs validation.
     * 
     * @param transformer1  the first transformer, not null
     * @param transformer2  the second transformer, not null
     * @return the <code>chained</code> transformer
     * @throws IllegalArgumentException if either transformer is null
     */
    public static Transformer getInstance(Transformer transformer1, Transformer transformer2) {
        if (transformer1 == null || transformer2 == null) {
            throw new IllegalArgumentException("Transformers must not be null");
        }
        Transformer[] transformers = new Transformer[] { transformer1, transformer2 };
        return new ChainedTransformer(transformers);
    }

    /**
     * Constructor that performs no validation.
     * Use <code>getInstance</code> if you want that.
     * 
     * @param transformers  the transformers to chain, not copied, no nulls
     */
    public ChainedTransformer(Transformer[] transformers) {
        super();
        iTransformers = transformers;
    }

    /**
     * Execute a list of transformers.
     * 
     * @param object  the input object passed to each transformer
     */
    public Object transform(Object object) {
        for (int i = 0; i < iTransformers.length; i++) {
            object = iTransformers[i].transform(object);
        }
        return object;
    }
    
}
