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There is a newer version: 2.12.15
/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.subst;

import ch.qos.logback.core.CoreConstants;
import ch.qos.logback.core.spi.ScanException;

import java.util.ArrayList;
import java.util.List;

public class Tokenizer {

    enum TokenizerState {
        LITERAL_STATE, START_STATE, DEFAULT_VAL_STATE
    }

    final String pattern;
    final int patternLength;

    public Tokenizer(String pattern) {
        this.pattern = pattern;
        patternLength = pattern.length();
    }

    TokenizerState state = TokenizerState.LITERAL_STATE;
    int pointer = 0;

    List tokenize() throws ScanException {
        List tokenList = new ArrayList();
        StringBuilder buf = new StringBuilder();

        while (pointer < patternLength) {
            char c = pattern.charAt(pointer);
            pointer++;

            switch (state) {
            case LITERAL_STATE:
                handleLiteralState(c, tokenList, buf);
                break;
            case START_STATE:
                handleStartState(c, tokenList, buf);
                break;
            case DEFAULT_VAL_STATE:
                handleDefaultValueState(c, tokenList, buf);
            default:
            }
        }
        // EOS
        switch (state) {
        case LITERAL_STATE:
            addLiteralToken(tokenList, buf);
            break;
        case DEFAULT_VAL_STATE:
            // trailing colon. see also LOGBACK-1140
            buf.append(CoreConstants.COLON_CHAR);
            addLiteralToken(tokenList, buf);
            break;
        case START_STATE:
         // trailing $. see also LOGBACK-1149
            buf.append(CoreConstants.DOLLAR);
            addLiteralToken(tokenList, buf);
            break;
        }
        return tokenList;
    }

    private void handleDefaultValueState(char c, List tokenList, StringBuilder stringBuilder) {
        switch (c) {
        case CoreConstants.DASH_CHAR:
            tokenList.add(Token.DEFAULT_SEP_TOKEN);
            state = TokenizerState.LITERAL_STATE;
            break;
        case CoreConstants.DOLLAR:
            stringBuilder.append(CoreConstants.COLON_CHAR);
            addLiteralToken(tokenList, stringBuilder);
            stringBuilder.setLength(0);
            state = TokenizerState.START_STATE;
            break;
        default:
            stringBuilder.append(CoreConstants.COLON_CHAR).append(c);
            state = TokenizerState.LITERAL_STATE;
            break;
        }
    }

    private void handleStartState(char c, List tokenList, StringBuilder stringBuilder) {
        if (c == CoreConstants.CURLY_LEFT) {
            tokenList.add(Token.START_TOKEN);
        } else {
            stringBuilder.append(CoreConstants.DOLLAR).append(c);
        }
        state = TokenizerState.LITERAL_STATE;
    }

    private void handleLiteralState(char c, List tokenList, StringBuilder stringBuilder) {
        if (c == CoreConstants.DOLLAR) {
            addLiteralToken(tokenList, stringBuilder);
            stringBuilder.setLength(0);
            state = TokenizerState.START_STATE;
        } else if (c == CoreConstants.COLON_CHAR) {
            addLiteralToken(tokenList, stringBuilder);
            stringBuilder.setLength(0);
            state = TokenizerState.DEFAULT_VAL_STATE;
        } else if (c == CoreConstants.CURLY_LEFT) {
            addLiteralToken(tokenList, stringBuilder);
            tokenList.add(Token.CURLY_LEFT_TOKEN);
            stringBuilder.setLength(0);
        } else if (c == CoreConstants.CURLY_RIGHT) {
            addLiteralToken(tokenList, stringBuilder);
            tokenList.add(Token.CURLY_RIGHT_TOKEN);
            stringBuilder.setLength(0);
        } else {
            stringBuilder.append(c);
        }

    }

    private void addLiteralToken(List tokenList, StringBuilder stringBuilder) {
        if (stringBuilder.length() == 0)
            return;
        tokenList.add(new Token(Token.Type.LITERAL, stringBuilder.toString()));
    }

}