package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

import org.apache.lucene.util.PriorityQueue;

import java.text.Collator;
import java.util.Locale;

/**
 * Expert: Collects sorted results from Searchable's and collates them.
 * The elements put into this queue must be of type FieldDoc.
 *
 * <p>Created: Feb 11, 2004 2:04:21 PM
 *
 * @author  Tim Jones (Nacimiento Software)
 * @since   lucene 1.4
 * @version $Id: FieldDocSortedHitQueue.java 472959 2006-11-09 16:21:50Z yonik $
 */
class FieldDocSortedHitQueue
extends PriorityQueue {

	// this cannot contain AUTO fields - any AUTO fields should
	// have been resolved by the time this class is used.
	volatile SortField[] fields;

	// used in the case where the fields are sorted by locale
	// based strings
	volatile Collator[] collators;


	/**
	 * Creates a hit queue sorted by the given list of fields.
	 * @param fields Fieldable names, in priority order (highest priority first).
	 * @param size  The number of hits to retain.  Must be greater than zero.
	 */
	FieldDocSortedHitQueue (SortField[] fields, int size) {
		this.fields = fields;
		this.collators = hasCollators (fields);
		initialize (size);
	}


	/**
	 * Allows redefinition of sort fields if they are <code>null</code>.
	 * This is to handle the case using ParallelMultiSearcher where the
	 * original list contains AUTO and we don't know the actual sort
	 * type until the values come back.  The fields can only be set once.
	 * This method is thread safe.
	 * @param fields
	 */
	synchronized void setFields (SortField[] fields) {
		if (this.fields == null) {
			this.fields = fields;
			this.collators = hasCollators (fields);
		}
	}


	/** Returns the fields being used to sort. */
	SortField[] getFields() {
		return fields;
	}


	/** Returns an array of collators, possibly <code>null</code>.  The collators
	 * correspond to any SortFields which were given a specific locale.
	 * @param fields Array of sort fields.
	 * @return Array, possibly <code>null</code>.
	 */
	private Collator[] hasCollators (final SortField[] fields) {
		if (fields == null) return null;
		Collator[] ret = new Collator[fields.length];
		for (int i=0; i<fields.length; ++i) {
			Locale locale = fields[i].getLocale();
			if (locale != null)
				ret[i] = Collator.getInstance (locale);
		}
		return ret;
	}


	/**
	 * Returns whether <code>a</code> is less relevant than <code>b</code>.
	 * @param a ScoreDoc
	 * @param b ScoreDoc
	 * @return <code>true</code> if document <code>a</code> should be sorted after document <code>b</code>.
	 */
	protected final boolean lessThan (final Object a, final Object b) {
		final FieldDoc docA = (FieldDoc) a;
		final FieldDoc docB = (FieldDoc) b;
		final int n = fields.length;
		int c = 0;
		for (int i=0; i<n && c==0; ++i) {
			final int type = fields[i].getType();
			switch (type) {
				case SortField.SCORE:
					float r1 = ((Float)docA.fields[i]).floatValue();
					float r2 = ((Float)docB.fields[i]).floatValue();
					if (r1 > r2) c = -1;
					if (r1 < r2) c = 1;
					break;
				case SortField.DOC:
				case SortField.INT:
					int i1 = ((Integer)docA.fields[i]).intValue();
					int i2 = ((Integer)docB.fields[i]).intValue();
					if (i1 < i2) c = -1;
					if (i1 > i2) c = 1;
					break;
				case SortField.STRING:
					String s1 = (String) docA.fields[i];
					String s2 = (String) docB.fields[i];
					// null values need to be sorted first, because of how FieldCache.getStringIndex()
					// works - in that routine, any documents without a value in the given field are
					// put first.  If both are null, the next SortField is used
					if (s1 == null) c = (s2==null) ? 0 : -1;
					else if (s2 == null) c = 1;  // 
					else if (fields[i].getLocale() == null) {
						c = s1.compareTo(s2);
					} else {
						c = collators[i].compare (s1, s2);
					}
					break;
				case SortField.FLOAT:
					float f1 = ((Float)docA.fields[i]).floatValue();
					float f2 = ((Float)docB.fields[i]).floatValue();
					if (f1 < f2) c = -1;
					if (f1 > f2) c = 1;
					break;
				case SortField.CUSTOM:
					c = docA.fields[i].compareTo (docB.fields[i]);
					break;
				case SortField.AUTO:
					// we cannot handle this - even if we determine the type of object (Float or
					// Integer), we don't necessarily know how to compare them (both SCORE and
					// FLOAT contain floats, but are sorted opposite of each other). Before
					// we get here, each AUTO should have been replaced with its actual value.
					throw new RuntimeException ("FieldDocSortedHitQueue cannot use an AUTO SortField");
				default:
					throw new RuntimeException ("invalid SortField type: "+type);
			}
			if (fields[i].getReverse()) {
				c = -c;
			}
		}

    // avoid random sort order that could lead to duplicates (bug #31241):
    if (c == 0)
      return docA.doc > docB.doc;

    return c > 0;
	}
}