/*
 * 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.
 */
package org.apache.logging.log4j.util;

import java.util.Collection;
import java.util.Map;

import aQute.bnd.annotation.Resolution;
import aQute.bnd.annotation.spi.ServiceProvider;

/**
 * PropertySource implementation that uses environment variables as a source.
 * All environment variables must begin with {@code LOG4J_} so as not to
 * conflict with other variables. Normalized environment variables follow a
 * scheme like this: {@code log4j2.fooBarProperty} would normalize to
 * {@code LOG4J_FOO_BAR_PROPERTY}.
 *
 * @since 2.10.0
 */
@ServiceProvider(value = PropertySource.class, resolution = Resolution.OPTIONAL)
public class EnvironmentPropertySource implements PropertySource {

    private static final String PREFIX = "LOG4J_";
    private static final int DEFAULT_PRIORITY = 100;

    @Override
    public int getPriority() {
        return DEFAULT_PRIORITY;
    }

    private void logException(final SecurityException e) {
        // There is no status logger yet.
        LowLevelLogUtil.logException(
                "The system environment variables are not available to Log4j due to security restrictions: " + e, e);
    }

    @Override
    public void forEach(final BiConsumer<String, String> action) {
        final Map<String, String> getenv;
        try {
            getenv = System.getenv();
        } catch (final SecurityException e) {
            logException(e);
            return;
        }
        for (final Map.Entry<String, String> entry : getenv.entrySet()) {
            final String key = entry.getKey();
            if (key.startsWith(PREFIX)) {
                action.accept(key.substring(PREFIX.length()), entry.getValue());
            }
        }
    }

    @Override
    public CharSequence getNormalForm(final Iterable<? extends CharSequence> tokens) {
        final StringBuilder sb = new StringBuilder("LOG4J");
        boolean empty = true;
        for (final CharSequence token : tokens) {
            empty = false;
            sb.append('_');
            for (int i = 0; i < token.length(); i++) {
                sb.append(Character.toUpperCase(token.charAt(i)));
            }
        }
        return empty ? null : sb.toString();
    }

    @Override
    public Collection<String> getPropertyNames() {
        try {
            return System.getenv().keySet();
        } catch (final SecurityException e) {
            logException(e);
            return PropertySource.super.getPropertyNames();
        }
    }

    @Override
    public String getProperty(final String key) {
        try {
            return System.getenv(key);
        } catch (final SecurityException e) {
            logException(e);
            return PropertySource.super.getProperty(key);
        }
    }

    @Override
    public boolean containsProperty(final String key) {
        try {
            return System.getenv().containsKey(key);
        } catch (final SecurityException e) {
            logException(e);
            return PropertySource.super.containsProperty(key);
        }
    }

}
