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.
/**
 * 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<Token> tokenize() throws ScanException {
        List<Token> tokenList = new ArrayList<Token>();
        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<Token> 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<Token> 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<Token> 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<Token> tokenList, StringBuilder stringBuilder) {
        if (stringBuilder.length() == 0)
            return;
        tokenList.add(new Token(Token.Type.LITERAL, stringBuilder.toString()));
    }

}