/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * 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 com.android.quicksearchbox;

import android.database.DataSetObservable;
import android.database.DataSetObserver;

import java.util.Collections;
import java.util.List;

/**
 * Abstract base class for corpus rankers.
 */
public abstract class AbstractCorpusRanker implements CorpusRanker
{
	private final DataSetObservable	mDataSetObservable	= new DataSetObservable();
	private final Corpora			mCorpora;
	
	// Cached list of ranked corpora. Set to null when mCorpora changes.
	private List<Corpus>			mRankedCorpora;

	public AbstractCorpusRanker(Corpora corpora)
	{
		mCorpora = corpora;
		mCorpora.registerDataSetObserver(new CorporaObserver());
	}

	/**
	 * Creates a ranked list of corpora.
	 */
	protected abstract List<Corpus> rankCorpora(Corpora corpora);

	public List<Corpus> getRankedCorpora()
	{
		if (mRankedCorpora == null)
		{
			//
			mRankedCorpora = Collections.unmodifiableList(rankCorpora(mCorpora));
		}
		return mRankedCorpora;
	}

	public void registerDataSetObserver(DataSetObserver observer)
	{
		mDataSetObservable.registerObserver(observer);
	}

	public void unregisterDataSetObserver(DataSetObserver observer)
	{
		mDataSetObservable.unregisterObserver(observer);
	}

	protected void notifyDataSetChanged()
	{
		mDataSetObservable.notifyChanged();
	}

	private class CorporaObserver extends DataSetObserver
	{
		@Override
		public void onChanged()
		{
			mRankedCorpora = null;
			notifyDataSetChanged();
		}
	}
}
