001// --------------------------------------------------------------------------------
002// Copyright 2002-2024 Echo Three, LLC
003//
004// Licensed under the Apache License, Version 2.0 (the "License");
005// you may not use this file except in compliance with the License.
006// You may obtain a copy of the License at
007//
008//     http://www.apache.org/licenses/LICENSE-2.0
009//
010// Unless required by applicable law or agreed to in writing, software
011// distributed under the License is distributed on an "AS IS" BASIS,
012// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013// See the License for the specific language governing permissions and
014// limitations under the License.
015// --------------------------------------------------------------------------------
016
017package com.echothree.model.control.sequence.server.logic.encoder;
018
019public class ReverseSwapSequenceEncoder
020        implements SequenceEncoder {
021
022    private ReverseSwapSequenceEncoder() {
023        super();
024    }
025
026    private static class SequenceEncoderHolder {
027        static SequenceEncoder instance = new ReverseSwapSequenceEncoder();
028    }
029
030    public static SequenceEncoder getInstance() {
031        return SequenceEncoderHolder.instance;
032    }
033
034    @Override
035    public String encode(String value) {
036        var codePoints = value.codePoints().toArray();
037        var result = new StringBuilder();
038        var length = codePoints.length;
039        var ending = length % 2;
040        var hasExtra = ending == 1;
041
042        for(int i = length - 1; i > (hasExtra ? 0 : -1); i -= 2) {
043            result.appendCodePoint(codePoints[i - 1]);
044            result.appendCodePoint(codePoints[i]);
045        }
046
047        if(hasExtra) {
048            result.appendCodePoint(codePoints[0]);
049        }
050
051        return result.toString();
052    }
053
054}