using Lucene.Net.Analysis.TokenAttributes;

namespace Lucene.Net.Analysis.Miscellaneous
{
    /*
	 * 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>
    /// A token filter for truncating the terms into a specific length.
    /// Fixed prefix truncation, as a stemming method, produces good results on Turkish language.
    /// It is reported that F5, using first 5 characters, produced best results in
    /// <a href="http://www.users.muohio.edu/canf/papers/JASIST2008offPrint.pdf">
    /// Information Retrieval on Turkish Texts</a>
    /// </summary>
    public sealed class TruncateTokenFilter : TokenFilter
    {
        private readonly ICharTermAttribute termAttribute;
        private readonly IKeywordAttribute keywordAttr;

        private readonly int length;

        public TruncateTokenFilter(TokenStream input, int length) 
            : base(input)
        {
            if (length < 1)
            {
                throw new System.ArgumentOutOfRangeException("length parameter must be a positive number: " + length);
            }
            this.length = length;
            this.termAttribute = AddAttribute<ICharTermAttribute>();
            this.keywordAttr = AddAttribute<IKeywordAttribute>();
        }

        public override sealed bool IncrementToken()
        {
            if (m_input.IncrementToken())
            {
                if (!keywordAttr.IsKeyword && termAttribute.Length > length)
                {
                    termAttribute.Length = length;
                }
                return true;
            }
            else
            {
                return false;
            }
        }
    }
}