/**
 *  Copyright 2005-2015 Red Hat, Inc.
 *
 *  Red Hat 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 io.fabric8.api.gravia;

/**
 * A provider for Runtime properties.
 *
 * @author thomas.diesler@jboss.com
 * @since 27-Sep-2013
 */
public interface PropertiesProvider {

    /**
     * Returns the value of the specified property. If the key is not found in
     * the Runtime properties, the system properties are then searched. The
     * method returns {@code null} if the property is not found.
     *
     * @param key The name of the requested property.
     * @return The value of the requested property, or {@code null} if the
     *         property is undefined.
     */
    Object getProperty(String key);

    /**
     * Returns the value of the specified property. If the key is not found in
     * the Runtime properties, the system properties are then searched. The
     * method throws an {@link IllegalStateException} if the property is not found.
     *
     * @param key The name of the requested property.
     * @return The value of the requested property
     * @throws IllegalStateException if the property is undefined.
     */
    Object getRequiredProperty(String key);
    
    /**
     * Returns the value of the specified property. If the key is not found in
     * the Runtime properties, the system properties are then searched. The
     * method returns provided default value if the property is not found.
     *
     * @param key The name of the requested property.
     * @return The value of the requested property, or the provided default value if the
     *         property is undefined.
     */
    Object getProperty(String key, Object defaultValue);
}
