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A thundr module enabling thundr for use on GAE (Google App Engine)
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/*
 * This file is a component of thundr, a software library from 3wks.
 * Read more: http://3wks.github.io/thundr/
 * Copyright (C) 2015 3wks, 
 *
 * 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.threewks.thundr.search.gae;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

import com.google.appengine.api.search.Cursor;
import com.google.appengine.api.search.Results;
import com.google.appengine.api.search.ScoredDocument;
import com.threewks.thundr.search.Result;
import com.threewks.thundr.search.SearchException;

public class ResultImpl implements Result {
	private Future> searchAsync;
	private Results results;
	private Integer offset;
	private List resultsList;
	private SearchExecutor searchExecutor;

	public ResultImpl(SearchExecutor searchExecutor, Future> searchAsync, Integer offset) {
		this.searchExecutor = searchExecutor;
		this.searchAsync = searchAsync;
		this.offset = offset;
	}

	/**
	 * TODO: The implementation of this only works in trivial situations. Further work will be done here
	 * in the future to allow the usage of the SearchService to store an entire document.
	 */
	@Override
	public List getResults() throws SearchException {
		return searchExecutor.getResults(resultsList());
	}

	@Override
	public List getResultIds() throws SearchException {
		return searchExecutor.getResultsAsIds(resultsList());
	}

	@Override
	public long getMatchingRecordCount() {
		Results results = results();
		return results.getNumberFound();
	}

	@Override
	public long getReturnedRecordCount() {
		Results results = results();
		return Math.max(0, results.getNumberReturned() - offset());
	}

	@Override
	public String cursor() {
		Cursor cursor = results.getCursor();
		return cursor == null ? null : cursor.toWebSafeString();
	}

	/**
	 * When applying an offset to a query in the Google Search service, you can no longer order by fields.
	 * To get around this, we apply the offset manually to the searched result set.
	 * 
	 * @return
	 */
	private List resultsList() {
		if (this.resultsList == null) {
			Results results = results();
			List resultsList = new ArrayList(results.getResults());
			int end = resultsList.size();
			int start = Math.min(offset(), end);
			this.resultsList = resultsList.subList(start, end);
		}
		return resultsList;
	}

	private Results results() {
		if (results == null) {
			try {
				results = searchAsync.get();
			} catch (InterruptedException e) {
				throw new SearchException(e, "Failed to retrieve search results: %s", e.getMessage());
			} catch (ExecutionException e) {
				throw new SearchException(e, "Failed to retrieve search results: %s", e.getMessage());
			}
		}
		return results;
	}

	private int offset() {
		return offset == null ? 0 : offset;
	}
}