/*
 * Copyright 2005 The Apache Software Foundation
 * 
 * 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.
 */
using System;
using PriorityQueue = Lucene.Net.Util.PriorityQueue;
namespace Lucene.Net.Search
{
	
    /// <summary>A Scorer for OR like queries, counterpart of Lucene's <code>ConjunctionScorer</code>.
    /// This Scorer implements {@link Scorer#SkipTo(int)} and uses SkipTo() on the given Scorers. 
    /// </summary>
    public class DisjunctionSumScorer : Scorer
    {
        /// <summary>The number of subscorers. </summary>
        private int nrScorers;
		
        /// <summary>The subscorers. </summary>
        protected internal System.Collections.IList subScorers;
		
        /// <summary>The minimum number of scorers that should match. </summary>
        private int minimumNrMatchers;
		
        /// <summary>The scorerQueue contains all subscorers ordered by their current Doc(),
        /// with the minimum at the top.
        /// <br>The scorerQueue is initialized the first time Next() or SkipTo() is called.
        /// <br>An exhausted scorer is immediately removed from the scorerQueue.
        /// <br>If less than the minimumNrMatchers scorers
        /// remain in the scorerQueue Next() and SkipTo() return false.
        /// <p>
        /// After each to call to Next() or SkipTo()
        /// <code>currentSumScore</code> is the total score of the current matching doc,
        /// <code>nrMatchers</code> is the number of matching scorers,
        /// and all scorers are after the matching doc, or are exhausted.
        /// </summary>
        private ScorerQueue scorerQueue = null;
		
        /// <summary>The document number of the current match. </summary>
        private int currentDoc = - 1;
		
        /// <summary>The number of subscorers that provide the current match. </summary>
        protected internal int nrMatchers = - 1;
		
        private float currentScore = System.Single.NaN;
		
        /// <summary>Construct a <code>DisjunctionScorer</code>.</summary>
        /// <param name="subScorers">A collection of at least two subscorers.
        /// </param>
        /// <param name="minimumNrMatchers">The positive minimum number of subscorers that should
        /// match to match this query.
        /// <br>When <code>minimumNrMatchers</code> is bigger than
        /// the number of <code>subScorers</code>,
        /// no matches will be produced.
        /// <br>When minimumNrMatchers equals the number of subScorers,
        /// it more efficient to use <code>ConjunctionScorer</code>.
        /// </param>
        public DisjunctionSumScorer(System.Collections.IList subScorers, int minimumNrMatchers):base(null)
        {
			
            nrScorers = subScorers.Count;
			
            if (minimumNrMatchers <= 0)
            {
                throw new System.ArgumentException("Minimum nr of matchers must be positive");
            }
            if (nrScorers <= 1)
            {
                throw new System.ArgumentException("There must be at least 2 subScorers");
            }
			
            this.minimumNrMatchers = minimumNrMatchers;
            this.subScorers = subScorers;
        }
		
        /// <summary>Construct a <code>DisjunctionScorer</code>, using one as the minimum number
        /// of matching subscorers.
        /// </summary>
        public DisjunctionSumScorer(System.Collections.IList subScorers):this(subScorers, 1)
        {
        }
		
        /// <summary>Called the first time Next() or SkipTo() is called to
        /// initialize <code>scorerQueue</code>.
        /// </summary>
        private void  InitScorerQueue()
        {
            System.Collections.IEnumerator si = subScorers.GetEnumerator();
            scorerQueue = new ScorerQueue(this, nrScorers);
            while (si.MoveNext())
            {
                Scorer se = (Scorer) si.Current;
                if (se.Next())
                {
                    // Doc() method will be used in scorerQueue.
                    scorerQueue.Insert(se);
                }
            }
        }
		
        /// <summary>A <code>PriorityQueue</code> that orders by {@link Scorer#Doc()}. </summary>
        private class ScorerQueue : PriorityQueue
        {
            private void  InitBlock(DisjunctionSumScorer enclosingInstance)
            {
                this.enclosingInstance = enclosingInstance;
            }
            private DisjunctionSumScorer enclosingInstance;
            public DisjunctionSumScorer Enclosing_Instance
            {
                get
                {
                    return enclosingInstance;
                }
				
            }
            internal ScorerQueue(DisjunctionSumScorer enclosingInstance, int size)
            {
                InitBlock(enclosingInstance);
                Initialize(size);
            }
			
            public override bool LessThan(System.Object o1, System.Object o2)
            {
                return ((Scorer) o1).Doc() < ((Scorer) o2).Doc();
            }
        }
		
        public override bool Next()
        {
            if (scorerQueue == null)
            {
                InitScorerQueue();
            }
            if (scorerQueue.Size() < minimumNrMatchers)
            {
                return false;
            }
            else
            {
                return AdvanceAfterCurrent();
            }
        }
		
		
        /// <summary>Advance all subscorers after the current document determined by the
        /// top of the <code>scorerQueue</code>.
        /// Repeat until at least the minimum number of subscorers match on the same
        /// document and all subscorers are after that document or are exhausted.
        /// <br>On entry the <code>scorerQueue</code> has at least <code>minimumNrMatchers</code>
        /// available. At least the scorer with the minimum document number will be advanced.
        /// </summary>
        /// <returns> true iff there is a match.
        /// <br>In case there is a match, </code>currentDoc</code>, </code>currentSumScore</code>,
        /// and </code>nrMatchers</code> describe the match.
        /// 
        /// </returns>
        /// <todo>  Investigate whether it is possible to use SkipTo() when </todo>
        /// <summary> the minimum number of matchers is bigger than one, ie. try and use the
        /// character of ConjunctionScorer for the minimum number of matchers.
        /// </summary>
        protected internal virtual bool AdvanceAfterCurrent()
        {
            do 
            {
                // repeat until minimum nr of matchers
                Scorer top = (Scorer) scorerQueue.Top();
                currentDoc = top.Doc();
                currentScore = top.Score();
                nrMatchers = 1;
                do 
                {
                    // Until all subscorers are after currentDoc
                    if (top.Next())
                    {
                        scorerQueue.AdjustTop();
                    }
                    else
                    {
                        scorerQueue.Pop();
                        if (scorerQueue.Size() < (minimumNrMatchers - nrMatchers))
                        {
                            // Not enough subscorers left for a match on this document,
                            // and also no more chance of any further match.
                            return false;
                        }
                        if (scorerQueue.Size() == 0)
                        {
                            break; // nothing more to advance, check for last match.
                        }
                    }
                    top = (Scorer) scorerQueue.Top();
                    if (top.Doc() != currentDoc)
                    {
                        break; // All remaining subscorers are after currentDoc.
                    }
                    else
                    {
                        currentScore += top.Score();
                        nrMatchers++;
                    }
                }
                while (true);
				
                if (nrMatchers >= minimumNrMatchers)
                {
                    return true;
                }
                else if (scorerQueue.Size() < minimumNrMatchers)
                {
                    return false;
                }
            }
            while (true);
        }
		
        /// <summary>Returns the score of the current document matching the query.
        /// Initially invalid, until {@link #Next()} is called the first time.
        /// </summary>
        public override float Score()
        {
            return currentScore;
        }
		
        public override int Doc()
        {
            return currentDoc;
        }
		
        /// <summary>Returns the number of subscorers matching the current document.
        /// Initially invalid, until {@link #Next()} is called the first time.
        /// </summary>
        public virtual int NrMatchers()
        {
            return nrMatchers;
        }
		
        /// <summary>Skips to the first match beyond the current whose document number is
        /// greater than or equal to a given target.
        /// <br>When this method is used the {@link #Explain(int)} method should not be used.
        /// <br>The implementation uses the SkipTo() method on the subscorers.
        /// </summary>
        /// <param name="target">The target document number.
        /// </param>
        /// <returns> true iff there is such a match.
        /// </returns>
        public override bool SkipTo(int target)
        {
            if (scorerQueue == null)
            {
                InitScorerQueue();
            }
            if (scorerQueue.Size() < minimumNrMatchers)
            {
                return false;
            }
            if (target <= currentDoc)
            {
                target = currentDoc + 1;
            }
            do 
            {
                Scorer top = (Scorer) scorerQueue.Top();
                if (top.Doc() >= target)
                {
                    return AdvanceAfterCurrent();
                }
                else if (top.SkipTo(target))
                {
                    scorerQueue.AdjustTop();
                }
                else
                {
                    scorerQueue.Pop();
                    if (scorerQueue.Size() < minimumNrMatchers)
                    {
                        return false;
                    }
                }
            }
            while (true);
        }
		
        /// <summary>Gives and explanation for the score of a given document.</summary>
        /// <todo>  Show the resulting score. See BooleanScorer.explain() on how to do this. </todo>
        public override Explanation Explain(int doc)
        {
            Explanation res = new Explanation();
            res.SetDescription("At least " + minimumNrMatchers + " of");
            System.Collections.IEnumerator ssi = subScorers.GetEnumerator();
            while (ssi.MoveNext())
            {
                res.AddDetail(((Scorer) ssi.Current).Explain(doc));
            }
            return res;
        }
    }
}