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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.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Properties;

import org.nosceon.connellite.PropertiesSupplier.Checkpoint;

/**
 * @author Johan Siebens
 */
class Poller {

    private static class State {

        private Checkpoint checkpoint = Checkpoint.INITIAL_CHECKPOINT;

        private PropertiesSupplier supplier;

        public State(PropertiesSupplier supplier) {
            this.supplier = supplier;
        }

        public PollResult update() throws Exception {
            PollResult s = supplier.poll(checkpoint);
            this.checkpoint = s.checkpoint();
            return s;
        }

    }

    protected static Node createNode(Collection> sources) {
        return createNode(resolvingProperties(sources));
    }

    private static Node createNode(ResolvingProperties cp) {
        Node newNode = Node.newNode();
        for (String key : cp.keys()) {
            newNode.add(key, cp.getProperty(key));
        }
        return newNode;
    }

    private static ResolvingProperties newResolvedProperties(Properties source, ResolvingProperties parent) {
        return new ResolvingProperties(source, parent);
    }

    private static ResolvingProperties resolvingProperties(Collection> suppliers) {
        ResolvingProperties cp = rootResolvedProperties();
        for (PollResult source : suppliers) {
            cp = newResolvedProperties(source.get(), cp);
        }
        return cp;
    }

    private static ResolvingProperties rootResolvedProperties() {
        return new ResolvingProperties();
    }

    private Node node = Node.newNode();

    private List states = new ArrayList<>();

    public Poller(List suppliers) {
        for (PropertiesSupplier supplier : suppliers) {
            states.add(new State(supplier));
        }
    }

    public PollResult poll() {
        try {
            boolean hasChanges = false;

            List> sources = new ArrayList<>();
            for (State state : states) {
                PollResult s = state.update();
                sources.add(s);
                hasChanges = hasChanges || s.hasChanges();
            }

            if (hasChanges) {
                node = createNode(sources);
            }

            return new PollResult(Checkpoint.INITIAL_CHECKPOINT, hasChanges, node);
        }
        catch (ConfigurationException e) {
            throw e;
        }
        catch (Exception e) {
            throw new ConfigurationException(e);
        }
    }

}