src/Lucene.Net.QueryParser/Classic/CharStream.cs

using System;
using System.IO;

namespace Lucene.Net.QueryParsers.Classic
{
    /*
     * 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> 
    /// This interface describes a character stream that maintains line and
    /// column number positions of the characters.  It also has the capability
    /// to backup the stream to some extent.  An implementation of this
    /// interface is used in the TokenManager implementation generated by
    /// JavaCCParser.
    /// 
    /// All the methods except <see cref="BackUp(int)"/> can be implemented in any fashion. <see cref="BackUp(int)"/>
    /// needs to be implemented correctly for the correct operation of the lexer.
    /// Rest of the methods are all used to get information like line number,
    /// column number and the string that constitutes a token and are not used
    /// by the lexer. Hence their implementation won't affect the generated lexer's
    /// operation.
    /// </summary>
    public interface ICharStream
    {
        /// <summary> 
        /// Returns the next character from the selected input.  The method
        /// of selecting the input is the responsibility of the class
        /// implementing this interface.  Can throw any <see cref="IOException"/>.
        /// </summary>
        char ReadChar();

        /// <summary>
        /// Returns the column position of the character last read.
        /// </summary>
        /// <seealso cref="EndColumn"/>
        [Obsolete]
        int Column { get; }

        /// <summary>
        /// Returns the line number of the character last read.
        /// </summary>
        /// <seealso cref="EndLine"/>
        [Obsolete]
        int Line { get; }

        /// <summary>
        /// Returns the column number of the last character for current token (being
        /// matched after the last call to BeginTOken).
        /// </summary>
        int EndColumn { get; }

        /// <summary> 
        /// Returns the line number of the last character for current token (being
        /// matched after the last call to BeginTOken).
        /// </summary>
        int EndLine { get; }

        /// <summary> 
        /// Returns the column number of the first character for current token (being
        /// matched after the last call to BeginTOken).
        /// </summary>
        int BeginColumn { get; }

        /// <summary> 
        /// Returns the line number of the first character for current token (being
        /// matched after the last call to BeginTOken).
        /// </summary>
        int BeginLine { get; }

        /// <summary> 
        /// Backs up the input stream by amount steps. Lexer calls this method if it
        /// had already read some characters, but could not use them to match a
        /// (longer) token. So, they will be used again as the prefix of the next
        /// token and it is the implemetation's responsibility to do this right.
        /// </summary>
        void BackUp(int amount);

        /// <summary> 
        /// Returns the next character that marks the beginning of the next token.
        /// All characters must remain in the buffer between two successive calls
        /// to this method to implement <see cref="BackUp(int)"/> correctly.
        /// </summary>
        char BeginToken();

        /// <summary> 
        /// Returns a string made up of characters from the marked token beginning
        /// to the current buffer position. Implementations have the choice of returning
        /// anything that they want to. For example, for efficiency, one might decide
        /// to just return null, which is a valid implementation.
        /// </summary>
        string Image { get; }

        /// <summary> 
        /// Returns an array of characters that make up the suffix of length 'len' for
        /// the currently matched token. This is used to build up the matched string
        /// for use in actions in the case of MORE. A simple and inefficient
        /// implementation of this is as follows :
        /// 
        /// <code>
        /// {
        ///     string t = Image;
        ///     return t.Substring(t.Length - len, len).ToCharArray();
        /// }
        /// </code>
        /// </summary>
        char[] GetSuffix(int len);
        
        /// <summary> 
        /// The lexer calls this function to indicate that it is done with the stream
        /// and hence implementations can free any resources held by this class.
        /// Again, the body of this function can be just empty and it will not
        /// affect the lexer's operation.
        /// </summary>
        void  Done();
    }
}