WildcardTermEnum.cs

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/* 
 * 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.
 */

using System;

using IndexReader = Lucene.Net.Index.IndexReader;
using Term = Lucene.Net.Index.Term;

namespace Lucene.Net.Search
{
    
    /// <summary> Subclass of FilteredTermEnum for enumerating all terms that match the
    /// specified wildcard filter term.
    /// <p/>
    /// Term enumerations are always ordered by Term.compareTo().  Each term in
    /// the enumeration is greater than all that precede it.
    /// </summary>
    public class WildcardTermEnum : FilteredTermEnum
    {
        internal Term searchTerm;
        internal System.String field;
        internal System.String text;
        internal System.String pre;
        internal int preLen;
        internal bool endEnum = false;
        
        /// <summary> Creates a new <c>WildcardTermEnum</c>.
        /// <p/>
        /// After calling the constructor the enumeration is already pointing to the first 
        /// valid term if such a term exists.
        /// </summary>
        public WildcardTermEnum(IndexReader reader, Term term):base()
        {
            searchTerm = term;
            field = searchTerm.Field;
            System.String searchTermText = searchTerm.Text;
            
            int sidx = searchTermText.IndexOf((System.Char) WILDCARD_STRING);
            int cidx = searchTermText.IndexOf((System.Char) WILDCARD_CHAR);
            int idx = sidx;
            if (idx == - 1)
            {
                idx = cidx;
            }
            else if (cidx >= 0)
            {
                idx = System.Math.Min(idx, cidx);
            }
            pre = idx != - 1?searchTerm.Text.Substring(0, (idx) - (0)):"";
            
            preLen = pre.Length;
            text = searchTermText.Substring(preLen);
            SetEnum(reader.Terms(new Term(searchTerm.Field, pre)));
        }

        /*protected internal*/ protected internal override bool TermCompare(Term term)
        {
            if ((System.Object) field == (System.Object) term.Field)
            {
                System.String searchText = term.Text;
                if (searchText.StartsWith(pre))
                {
                    return WildcardEquals(text, 0, searchText, preLen);
                }
            }
            endEnum = true;
            return false;
        }
        
        public override float Difference()
        {
            return 1.0f;
        }
        
        public override bool EndEnum()
        {
            return endEnum;
        }
        
        /// <summary>*****************************************
        /// String equality with support for wildcards
        /// ******************************************
        /// </summary>
        
        public const char WILDCARD_STRING = '*';
        public const char WILDCARD_CHAR = '?';
        
        /// <summary> Determines if a word matches a wildcard pattern.
        /// <small>Work released by Granta Design Ltd after originally being done on
        /// company time.</small>
        /// </summary>
        public static bool WildcardEquals(System.String pattern, int patternIdx, System.String string_Renamed, int stringIdx)
        {
            int p = patternIdx;
            
            for (int s = stringIdx; ; ++p, ++s)
            {
                // End of string yet?
                bool sEnd = (s >= string_Renamed.Length);
                // End of pattern yet?
                bool pEnd = (p >= pattern.Length);
                
                // If we're looking at the end of the string...
                if (sEnd)
                {
                    // Assume the only thing left on the pattern is/are wildcards
                    bool justWildcardsLeft = true;
                    
                    // Current wildcard position
                    int wildcardSearchPos = p;
                    // While we haven't found the end of the pattern,
                    // and haven't encountered any non-wildcard characters
                    while (wildcardSearchPos < pattern.Length && justWildcardsLeft)
                    {
                        // Check the character at the current position
                        char wildchar = pattern[wildcardSearchPos];
                        
                        // If it's not a wildcard character, then there is more
                        // pattern information after this/these wildcards.
                        if (wildchar != WILDCARD_CHAR && wildchar != WILDCARD_STRING)
                        {
                            justWildcardsLeft = false;
                        }
                        else
                        {
                            // to prevent "cat" matches "ca??"
                            if (wildchar == WILDCARD_CHAR)
                            {
                                return false;
                            }
                            
                            // Look at the next character
                            wildcardSearchPos++;
                        }
                    }
                    
                    // This was a prefix wildcard search, and we've matched, so
                    // return true.
                    if (justWildcardsLeft)
                    {
                        return true;
                    }
                }
                
                // If we've gone past the end of the string, or the pattern,
                // return false.
                if (sEnd || pEnd)
                {
                    break;
                }
                
                // Match a single character, so continue.
                if (pattern[p] == WILDCARD_CHAR)
                {
                    continue;
                }
                
                //
                if (pattern[p] == WILDCARD_STRING)
                {
                    // Look at the character beyond the '*' characters.
                    while (p < pattern.Length && pattern[p] == WILDCARD_STRING)
                        ++p;
                    // Examine the string, starting at the last character.
                    for (int i = string_Renamed.Length; i >= s; --i)
                    {
                        if (WildcardEquals(pattern, p, string_Renamed, i))
                        {
                            return true;
                        }
                    }
                    break;
                }
                if (pattern[p] != string_Renamed[s])
                {
                    break;
                }
            }
            return false;
        }
    }
}