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

using System;
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.
    /// </summary>
    public class GradientFormatter : IFormatter
    {
        private float maxScore;

        protected int m_fgRMin, m_fgGMin, m_fgBMin;
        protected int m_fgRMax, m_fgGMax, m_fgBMax;
        protected bool m_highlightForeground;
        protected int m_bgRMin, m_bgGMin, m_bgBMin;
        protected int m_bgRMax, m_bgGMax, m_bgBMax;
        protected bool m_highlightBackground;

        /// <summary> Sets the color range for the IDF scores</summary>
        /// <param name="maxScore">
        /// The score (and above) displayed as maxColor (See <see cref="QueryScorer.MaxTermWeight"/>
        /// which can be used to callibrate scoring scale)
        /// </param>
        /// <param name="minForegroundColor">
        /// The hex color used for representing IDF scores of zero eg
        /// #FFFFFF (white) or null if no foreground color required
        /// </param>
        /// <param name="maxForegroundColor">
        /// The largest hex color used for representing IDF scores eg
        /// #000000 (black) or null if no foreground color required
        /// </param>
        /// <param name="minBackgroundColor">
        /// The hex color used for representing IDF scores of zero eg
        /// #FFFFFF (white) or null if no background color required
        /// </param>
        /// <param name="maxBackgroundColor">
        /// The largest hex color used for representing IDF scores eg
        /// #000000 (black) or null if no background color required
        /// </param>
        public GradientFormatter(float maxScore, string minForegroundColor, 
            string maxForegroundColor, string minBackgroundColor, 
            string maxBackgroundColor)
        {
            m_highlightForeground = (minForegroundColor != null) && (maxForegroundColor != null);

            if (m_highlightForeground)
            {
                if (minForegroundColor.Length != 7)
                {
                    throw new ArgumentException("minForegroundColor is not 7 bytes long eg a hex " 
                        + "RGB value such as #FFFFFF");
                }
                if (maxForegroundColor.Length != 7)
                {
                    throw new ArgumentException("minForegroundColor is not 7 bytes long eg a hex " 
                        + "RGB value such as #FFFFFF");
                }
                m_fgRMin = HexToInt32(minForegroundColor.Substring(1, 3 - 1));
                m_fgGMin = HexToInt32(minForegroundColor.Substring(3, 5 - 3));
                m_fgBMin = HexToInt32(minForegroundColor.Substring(5, 7 - 5));

                m_fgRMax = HexToInt32(maxForegroundColor.Substring(1, 3 - 1));
                m_fgGMax = HexToInt32(maxForegroundColor.Substring(3, 5 - 3));
                m_fgBMax = HexToInt32(maxForegroundColor.Substring(5, 7 - 5));
            }

            m_highlightBackground = (minBackgroundColor != null) 
                && (maxBackgroundColor != null);
            if (m_highlightBackground)
            {
                if (minBackgroundColor.Length != 7)
                {
                    throw new ArgumentException("minBackgroundColor is not 7 bytes long eg a hex " 
                        + "RGB value such as #FFFFFF");
                }
                if (maxBackgroundColor.Length != 7)
                {
                    throw new ArgumentException("minBackgroundColor is not 7 bytes long eg a hex " 
                        + "RGB value such as #FFFFFF");
                }
                m_bgRMin = HexToInt32(minBackgroundColor.Substring(1, 3 - 1));
                m_bgGMin = HexToInt32(minBackgroundColor.Substring(3, 5 - 3));
                m_bgBMin = HexToInt32(minBackgroundColor.Substring(5, 7 - 5));

                m_bgRMax = HexToInt32(maxBackgroundColor.Substring(1, 3 - 1));
                m_bgGMax = HexToInt32(maxBackgroundColor.Substring(3, 5 - 3));
                m_bgBMax = HexToInt32(maxBackgroundColor.Substring(5, 7 - 5));
            }
            //        this.corpusReader = corpusReader;
            this.maxScore = maxScore;
            //        totalNumDocs = corpusReader.numDocs();
        }

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

            var sb = new StringBuilder();
            sb.Append("<font ");
            if (m_highlightForeground)
            {
                sb.Append("color=\"");
                sb.Append(GetForegroundColorString(score));
                sb.Append("\" ");
            }
            if (m_highlightBackground)
            {
                sb.Append("bgcolor=\"");
                sb.Append(GetBackgroundColorString(score));
                sb.Append("\" ");
            }
            sb.Append(">");
            sb.Append(originalText);
            sb.Append("</font>");
            return sb.ToString();
        }

        protected internal virtual string GetForegroundColorString(float score)
        {
            int rVal = GetColorVal(m_fgRMin, m_fgRMax, score);
            int gVal = GetColorVal(m_fgGMin, m_fgGMax, score);
            int bVal = GetColorVal(m_fgBMin, m_fgBMax, score);
            var sb = new StringBuilder();
            sb.Append("#");
            sb.Append(Int32ToHex(rVal));
            sb.Append(Int32ToHex(gVal));
            sb.Append(Int32ToHex(bVal));
            return sb.ToString();
        }

        protected internal virtual string GetBackgroundColorString(float score)
        {
            int rVal = GetColorVal(m_bgRMin, m_bgRMax, score);
            int gVal = GetColorVal(m_bgGMin, m_bgGMax, score);
            int bVal = GetColorVal(m_bgBMin, m_bgBMax, score);
            var sb = new StringBuilder();
            sb.Append("#");
            sb.Append(Int32ToHex(rVal));
            sb.Append(Int32ToHex(gVal));
            sb.Append(Int32ToHex(bVal));
            return sb.ToString();
        }

        private int GetColorVal(int colorMin, int colorMax, float score)
        {
            if (colorMin == colorMax)
            {
                return colorMin;
            }
            float scale = Math.Abs(colorMin - colorMax);
            float relScorePercent = Math.Min(maxScore, score) / maxScore;
            float colScore = scale * relScorePercent;
            return Math.Min(colorMin, colorMax) + (int)colScore;
        }

        private static char[] hexDigits = new char[] { '0', '1', '2', '3', '4', '5', '6', '7',
            '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

        /// <summary>
        /// NOTE: This was intToHex() in Lucene
        /// </summary>
        private static string Int32ToHex(int i)
        {
            return "" + hexDigits[(i & 0xF0) >> 4] + hexDigits[i & 0x0F];
        }

        /// <summary> 
        /// Converts a hex string into an <see cref="int"/>.
        /// <para/>
        /// NOTE: This was hexToInt() in Lucene
        /// </summary>
        /// <param name="hex">
        /// A string in capital or lower case hex, of no more then 16
        /// characters.
        /// </param>
        /// <exception cref="FormatException">if the string is more than 16 characters long, or if any
        /// character is not in the set [0-9a-fA-f]</exception>
        public static int HexToInt32(string hex)
        {
            int len = hex.Length;
            if (len > 16)
                throw new FormatException();

            try
            {
                // LUCENENET NOTE: Convert.ToInt32(string, int) throws a
                // FormatException if the character does not fall in
                // the correct range, which is the behavior we are expecting.
                // But throws an ArgumentException if passed a negative number.
                // So we need to convert to FormatException to provide the correct behavior.
                return Convert.ToInt32(hex, 16);
            }
            catch (ArgumentException e)
            {
                throw new FormatException(e.Message, e);
            }
        }
    }
}