src/Lucene.Net.Highlighter/Highlight/SpanGradientFormatter.cs

using System.Text;

namespace Lucene.Net.Search.Highlight
{
    /*
     * 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>
    /// Formats text with different color intensity depending on the score of the
    /// term using the span tag. <see cref="GradientFormatter"/> uses a bgcolor argument to the font tag which
    /// doesn't work in Mozilla, thus this class.
    /// </summary>
    /// <seealso cref="GradientFormatter"/>
    public class SpanGradientFormatter : GradientFormatter
    {
        // guess how much extra text we'll add to the text we're highlighting to try to avoid a  StringBuilder resize
        private static readonly string TEMPLATE = "<span style=\"background: #EEEEEE; color: #000000;\">...</span>";
        private static readonly int EXTRA = TEMPLATE.Length;

        public SpanGradientFormatter(float maxScore, string minForegroundColor,
                                     string maxForegroundColor, string minBackgroundColor,
                                     string maxBackgroundColor)
            : base(maxScore, minForegroundColor, maxForegroundColor, minBackgroundColor, maxBackgroundColor)
        { }

        public override string HighlightTerm(string originalText, TokenGroup tokenGroup)
        {
            if (tokenGroup.TotalScore == 0)
                return originalText;
            float score = tokenGroup.TotalScore;
            if (score == 0)
            {
                return originalText;
            }

            // try to size sb correctly
            var sb = new StringBuilder(originalText.Length + EXTRA);

            sb.Append("<span style=\"");
            if (m_highlightForeground)
            {
                sb.Append("color: ");
                sb.Append(GetForegroundColorString(score));
                sb.Append("; ");
            }
            if (m_highlightBackground)
            {
                sb.Append("background: ");
                sb.Append(GetBackgroundColorString(score));
                sb.Append("; ");
            }
            sb.Append("\">");
            sb.Append(originalText);
            sb.Append("</span>");
            return sb.ToString();
        }
    }
}