src/Lucene.Net.Join/TermsCollector.cs

using Lucene.Net.Index;
using Lucene.Net.Search;
using Lucene.Net.Util;

namespace Lucene.Net.Join
{
    /*
     * 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.
     */

    /// <summary>
    /// A collector that collects all terms from a specified field matching the query.
    /// 
    /// @lucene.experimental
    /// </summary>
    internal abstract class TermsCollector : ICollector
    {
        private readonly string _field;
        private readonly BytesRefHash _collectorTerms = new BytesRefHash();

        internal TermsCollector(string field)
        {
            _field = field;
        }

        public virtual BytesRefHash CollectorTerms => _collectorTerms;

        public virtual void SetScorer(Scorer scorer)
        {
        }

        // LUCENENET specific - we need to implement these here, since our abstract base class
        // is now an interface.

        /// <summary>
        /// Called once for every document matching a query, with the unbased document
        /// number.
        /// <para/>Note: The collection of the current segment can be terminated by throwing
        /// a <see cref="CollectionTerminatedException"/>. In this case, the last docs of the
        /// current <see cref="AtomicReaderContext"/> will be skipped and <see cref="IndexSearcher"/>
        /// will swallow the exception and continue collection with the next leaf.
        /// <para/>
        /// Note: this is called in an inner search loop. For good search performance,
        /// implementations of this method should not call <see cref="IndexSearcher.Doc(int)"/> or
        /// <see cref="Lucene.Net.Index.IndexReader.Document(int)"/> on every hit.
        /// Doing so can slow searches by an order of magnitude or more.
        /// </summary>
        public abstract void Collect(int doc);

        /// <summary>
        /// Called before collecting from each <see cref="AtomicReaderContext"/>. All doc ids in
        /// <see cref="Collect(int)"/> will correspond to <see cref="Index.IndexReaderContext.Reader"/>.
        ///
        /// Add <see cref="AtomicReaderContext.DocBase"/> to the current <see cref="Index.IndexReaderContext.Reader"/>'s
        /// internal document id to re-base ids in <see cref="Collect(int)"/>.
        /// </summary>
        /// <param name="context">next atomic reader context </param>
        public abstract void SetNextReader(AtomicReaderContext context);


        public virtual bool AcceptsDocsOutOfOrder => true;

        /// <summary>
        /// Chooses the right <see cref="TermsCollector"/> implementation.
        /// </summary>
        /// <param name="field">The field to collect terms for.</param>
        /// <param name="multipleValuesPerDocument">Whether the field to collect terms for has multiple values per document.</param>
        /// <returns>A <see cref="TermsCollector"/> instance.</returns>
        internal static TermsCollector Create(string field, bool multipleValuesPerDocument)
        {
            return multipleValuesPerDocument ? (TermsCollector) new MV(field) : new SV(field);
        }

        // impl that works with multiple values per document
        private class MV : TermsCollector
        {
            private readonly BytesRef _scratch = new BytesRef();
            private SortedSetDocValues _docTermOrds;

            internal MV(string field) 
                : base(field)
            {
            }
            
            public override void Collect(int doc)
            {
                _docTermOrds.SetDocument(doc);
                long ord;
                while ((ord = _docTermOrds.NextOrd()) != SortedSetDocValues.NO_MORE_ORDS)
                {
                    _docTermOrds.LookupOrd(ord, _scratch);
                    _collectorTerms.Add(_scratch);
                }
            }
            
            public override void SetNextReader(AtomicReaderContext context)
            {
                _docTermOrds = FieldCache.DEFAULT.GetDocTermOrds(context.AtomicReader, _field);
            }
        }

        // impl that works with single value per document
        private class SV : TermsCollector
        {
            private readonly BytesRef _spare = new BytesRef();
            private BinaryDocValues _fromDocTerms;

            internal SV(string field) 
                : base(field)
            {
            }
            
            public override void Collect(int doc)
            {
                _fromDocTerms.Get(doc, _spare);
                _collectorTerms.Add(_spare);
            }
            
            public override void SetNextReader(AtomicReaderContext context)
            {
                _fromDocTerms = FieldCache.DEFAULT.GetTerms(context.AtomicReader, _field, false);
            }
        }
    }
}