org.jboss.logging.processor.util.Expressions Maven / Gradle / Ivy

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 * JBoss, Home of Professional Open Source.
 *
 * Copyright 2023 Red Hat, Inc., and individual contributors
 * as indicated by the @author tags.
 *
 * Licensed 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.
 */

package org.jboss.logging.processor.util;

import java.util.Properties;

/**
 * @author James R. Perkins
 */
public class Expressions {

    private static final int INITIAL = 0;
    private static final int GOT_DOLLAR = 1;
    private static final int GOT_OPEN_BRACE = 2;
    private static final int RESOLVED = 3;
    private static final int DEFAULT = 4;

    public static String resolve(final Properties props, final String expression) {
        if (expression == null)
            return null;
        final StringBuilder builder = new StringBuilder();
        final char[] chars = expression.toCharArray();
        final int len = chars.length;
        int state = 0;
        int start = -1;
        int nameStart = -1;
        for (int i = 0; i < len; i++) {
            char ch = chars[i];
            switch (state) {
                case INITIAL: {
                    switch (ch) {
                        case '$': {
                            state = GOT_DOLLAR;
                            continue;
                        }
                        default: {
                            builder.append(ch);
                            continue;
                        }
                    }
                    // not reachable
                }
                case GOT_DOLLAR: {
                    switch (ch) {
                        case '$': {
                            builder.append(ch);
                            state = INITIAL;
                            continue;
                        }
                        case '{': {
                            start = i + 1;
                            nameStart = start;
                            state = GOT_OPEN_BRACE;
                            continue;
                        }
                        default: {
                            // invalid; emit and resume
                            builder.append('$').append(ch);
                            state = INITIAL;
                            continue;
                        }
                    }
                    // not reachable
                }
                case GOT_OPEN_BRACE: {
                    switch (ch) {
                        case ':':
                        case '}':
                        case ',': {
                            final String name = expression.substring(nameStart, i).trim();
                            final String val;
                            if (name.startsWith("env.")) {
                                val = System.getenv(name.substring(4));
                            } else if (name.startsWith("sys.")) {
                                val = System.getProperty(name.substring(4));
                            } else {
                                val = props.getProperty(name);
                            }
                            if (val != null) {
                                builder.append(val);
                                state = ch == '}' ? INITIAL : RESOLVED;
                                continue;
                            } else if (ch == ',') {
                                nameStart = i + 1;
                                continue;
                            } else if (ch == ':') {
                                start = i + 1;
                                state = DEFAULT;
                                continue;
                            } else {
                                builder.append(expression.substring(start - 2, i + 1));
                                state = INITIAL;
                                continue;
                            }
                        }
                        default: {
                            continue;
                        }
                    }
                    // not reachable
                }
                case RESOLVED: {
                    if (ch == '}') {
                        state = INITIAL;
                    }
                    continue;
                }
                case DEFAULT: {
                    if (ch == '}') {
                        state = INITIAL;
                        builder.append(expression.substring(start, i));
                    }
                    continue;
                }
                default:
                    throw new IllegalStateException();
            }
        }
        switch (state) {
            case GOT_DOLLAR: {
                builder.append('$');
                break;
            }
            case DEFAULT:
            case GOT_OPEN_BRACE: {
                builder.append(expression.substring(start - 2));
                break;
            }
        }
        return builder.toString();
    }
}