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/*
 * Copyright 2013 the original author or authors.
 *
 * 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.nosceon.connellite;

import java.util.Properties;

/**
 * @author Johan Siebens
 */
public abstract class PropertiesSupplier {

    public static class Checkpoint {

        public static Checkpoint INITIAL_CHECKPOINT = new Checkpoint(-1);

        private final long value;

        public Checkpoint(long value) {
            this.value = value;
        }

        public long value() {
            return value;
        }

    }

    private long lastModification;

    private Properties properties;

    public synchronized PollResult poll(Checkpoint checkpoint) throws Exception {
        long now = System.currentTimeMillis();
        if (properties == null) {
            this.properties = loadProperties();
            this.lastModification = now;
            return new PollResult(new Checkpoint(lastModification), true, properties);
        }
        else {
            if (isExpired()) {
                Properties newProperties = loadProperties();
                if (!properties.equals(newProperties)) {
                    this.lastModification = now;
                    this.properties = newProperties;
                    return new PollResult(new Checkpoint(lastModification), true, properties);
                }
                else {
                    return new PollResult(new Checkpoint(lastModification), false, properties);
                }
            }
            else {
                return new PollResult(new Checkpoint(lastModification), checkpoint.value() != this.lastModification, properties);
            }
        }
    }

    protected abstract boolean isExpired();

    protected abstract Properties loadProperties() throws Exception;

}