package api;

import java.util.ArrayList;

import java.util.Collection;

import java.util.Collections;

import java.util.HashSet;

import java.util.Iterator;

import java.util.List;

import java.util.Set;

/** Simplified version of NetBeans 

 * <a href="http://bits.netbeans.org/6.0/javadoc/org-openide-util/org/openide/util/Lookup.html">Lookup</a>

 * reimplemented to separate the API for clients

 * from the API for implementators while guaranteeing

 * consistency among all there methods.

 *

 * @author Jaroslav Tulach <jtulach@netbeans.org>

 * @version 2.0

 */

// BEGIN: design.consistency.2.0

public abstract class Lookup {

    /** only for classes in the same package */

    Lookup() {

    }

    // BEGIN: design.consistency.lookup.2.0

    public <T> T lookup(Class<T> clazz) {

        Iterator<T> it = doLookup(clazz);

        return it.hasNext() ? it.next() : null;

    }

    // END: design.consistency.lookup.2.0

    // BEGIN: design.consistency.lookupAll.2.0

    public <T> Collection<? extends T> lookupAll(Class<T> clazz) {

        Iterator<T> it = doLookup(clazz);

        if (!it.hasNext()) {

            return Collections.emptyList();

        } else {

            List<T> result = new ArrayList<T>();

            while (it.hasNext()) {

                result.add(it.next());

            }

            return result;

        }

    }

    // END: design.consistency.lookupAll.2.0

    // BEGIN: design.consistency.lookupAllClasses.2.0

    public <T> Set<Class<? extends T>> lookupAllClasses(Class<T> clazz) {

        Iterator<T> it = doLookup(clazz);

        if (!it.hasNext()) {

            return Collections.emptySet();

        } else {

            Set<Class<? extends T>> result = 

                new HashSet<Class<? extends T>>();

            while (it.hasNext()) {

                result.add(it.next().getClass().asSubclass(clazz));

            }

            return result;

        }

    }

    // END: design.consistency.lookupAllClasses.2.0

// FINISH: design.consistency.2.0

    abstract <T> Iterator<T> doLookup(Class<T> clazz);

}