src/Lucene.Net.Analysis.Common/Analysis/CharFilter/BaseCharFilter.cs

using J2N.Numerics;
using Lucene.Net.Diagnostics;
using Lucene.Net.Support;
using Lucene.Net.Util;
using System.Diagnostics;
using System.IO;

namespace Lucene.Net.Analysis.CharFilters
{
    /*
     * 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>
    /// Base utility class for implementing a <see cref="CharFilter"/>.
    /// You subclass this, and then record mappings by calling
    /// <see cref="AddOffCorrectMap"/>, and then invoke the correct
    /// method to correct an offset.
    /// </summary>
    public abstract class BaseCharFilter : CharFilter
    {

        private int[] offsets;
        private int[] diffs;
        private int size = 0;

        public BaseCharFilter(TextReader @in)
            : base(@in)
        {
        }

        /// <summary>
        /// Retrieve the corrected offset. </summary>
        protected override int Correct(int currentOff)
        {
            if (offsets == null || currentOff < offsets[0])
            {
                return currentOff;
            }

            int hi = size - 1;
            if (currentOff >= offsets[hi])
            {
                return currentOff + diffs[hi];
            }

            int lo = 0;
            int mid = -1;

            while (hi >= lo)
            {
                mid = (lo + hi).TripleShift(1);
                if (currentOff < offsets[mid])
                {
                    hi = mid - 1;
                }
                else if (currentOff > offsets[mid])
                {
                    lo = mid + 1;
                }
                else
                {
                    return currentOff + diffs[mid];
                }
            }

            if (currentOff < offsets[mid])
            {
                return mid == 0 ? currentOff : currentOff + diffs[mid - 1];
            }
            else
            {
                return currentOff + diffs[mid];
            }
        }

        protected virtual int LastCumulativeDiff => offsets == null ? 0 : diffs[size - 1];

        /// <summary>
        /// <para>
        ///   Adds an offset correction mapping at the given output stream offset.
        /// </para>
        /// <para>
        ///   Assumption: the offset given with each successive call to this method
        ///   will not be smaller than the offset given at the previous invocation.
        /// </para>
        /// </summary>
        /// <param name="off"> The output stream offset at which to apply the correction </param>
        /// <param name="cumulativeDiff"> The input offset is given by adding this
        ///                       to the output offset </param>
        protected virtual void AddOffCorrectMap(int off, int cumulativeDiff)
        {
            if (offsets == null)
            {
                offsets = new int[64];
                diffs = new int[64];
            }
            else if (size == offsets.Length)
            {
                offsets = ArrayUtil.Grow(offsets);
                diffs = ArrayUtil.Grow(diffs);
            }

            int offset = offsets[(size == 0) ? 0 : size - 1];
            if (Debugging.AssertsEnabled) Debugging.Assert(size == 0 || off >= offset, "Offset #{0}({1}) is less than the last recorded offset {2}\n{3}\n{4}", size, off, offset, offsets, diffs);

            if (size == 0 || off != offsets[size - 1])
            {
                offsets[size] = off;
                diffs[size++] = cumulativeDiff;
            } // Overwrite the diff at the last recorded offset
            else
            {
                diffs[size - 1] = cumulativeDiff;
            }
        }
    }
}