Copyright 2014 Netflix, Inc.
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.
/**
 * Copyright 2014 Netflix, Inc.
 *
 * 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 com.netflix.config;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import com.google.common.base.Splitter;
import com.google.common.base.Strings;
import com.google.common.collect.Lists;

This class delegates to a regex (default is comma) delimited dynamic string property and 
returns a dynamic list of a generic type which is transformed from string.
Author:
awang/**
 * This class delegates to a regex (default is comma) delimited dynamic string property and 
 * returns a dynamic list of a generic type which is transformed from string.
 * 
 * @author awang
 */
public abstract class DynamicListProperty<T> implements Property<List<T>> {
    private volatile List<T> values;

    private List<T> defaultValues;
    
    private DynamicStringProperty delegate;

    private Splitter splitter;

    public static final String DEFAULT_DELIMITER = ",";

    
Create the dynamic list property using default delimiter regex ",". The guava Splitter used is created as
Splitter.onPattern(delimiterRegex).omitEmptyStrings().trimResults(). The default
list value will be transformed from list of strings after splitting. If defaultValue string is
null, the default list value will be an empty list.
/**
     * Create the dynamic list property using default delimiter regex ",". The guava Splitter used is created as
     * <code>Splitter.onPattern(delimiterRegex).omitEmptyStrings().trimResults()</code>. The default
     * list value will be transformed from list of strings after splitting. If defaultValue string is
     * null, the default list value will be an empty list.
     */
    public DynamicListProperty(String propName, String defaultValue) {
        this(propName, defaultValue, DEFAULT_DELIMITER);
    }

    
Create the dynamic list property. The guava Splitter used is created as
Splitter.onPattern(delimiterRegex).omitEmptyStrings().trimResults(). The default
list value will be transformed from list of strings after splitting. If defaultValue string is
null, the default list value will be an empty list.
/**
     * Create the dynamic list property. The guava Splitter used is created as
     * <code>Splitter.onPattern(delimiterRegex).omitEmptyStrings().trimResults()</code>. The default
     * list value will be transformed from list of strings after splitting. If defaultValue string is
     * null, the default list value will be an empty list.
     */
    public DynamicListProperty(String propName, String defaultValue, String delimiterRegex) {
        this.splitter = Splitter.onPattern(delimiterRegex).omitEmptyStrings().trimResults();
        setup(propName, transform(split(defaultValue)), splitter);
    }

    public DynamicListProperty(String propName, List<T> defaultValue) {
        this(propName, defaultValue, DEFAULT_DELIMITER);
    }

    
Create the dynamic list property. The guava Splitter used is created as
Splitter.onPattern(delimiterRegex).omitEmptyStrings().trimResults(). The default
list value will be taken from the passed in list argument.
/**
     * Create the dynamic list property. The guava Splitter used is created as
     * <code>Splitter.onPattern(delimiterRegex).omitEmptyStrings().trimResults()</code>. The default
     * list value will be taken from the passed in list argument.
     */
    public DynamicListProperty(String propName, List<T> defaultValue, String delimiterRegex) {
        setup(propName, defaultValue, delimiterRegex);
    }

    
Create the dynamic list property using the splitter and default list value passed in 
from the arguments.
/**
     * Create the dynamic list property using the splitter and default list value passed in 
     * from the arguments.
     */
    public DynamicListProperty(String propName, List<T> defaultValue, Splitter splitter) {
        setup(propName, defaultValue, splitter);
    }

    
    private void setup(String propName, List<T> defaultValue, String delimiterRegex) {
        setup(propName, defaultValue, Splitter.onPattern(delimiterRegex).omitEmptyStrings().trimResults());
    }

    private void setup(String propName, List<T> defaultValue, Splitter splitter) {
        // Make a defensive copy of the default value. Would prefer to use an ImmutableList, but that
        // does not allow for null values in the List.
        this.defaultValues = (defaultValue == null ? null : 
            Collections.unmodifiableList(new ArrayList<T>(defaultValue)));
        
        this.splitter = splitter;
        delegate = DynamicPropertyFactory.getInstance().getStringProperty(propName, null);
        load();
        Runnable callback = new Runnable() {
            @Override
            public void run() {
                propertyChangedInternal();
            }
        };
        delegate.addCallback(callback);
    }

    private void propertyChangedInternal() {
        load();
        propertyChanged();
    }

    
A method invoked when the underlying string property is changed. Default implementation does nothing. 
Subclass can override this method 
to receive callback. 
/**
     * A method invoked when the underlying string property is changed. Default implementation does nothing. 
     * Subclass can override this method 
     * to receive callback. 
     */
    protected void propertyChanged() {
    }

    
Get the list type from the underlying dynamic string property. If the property is undefined, this method
returns the default list value.   
/**
     * Get the list type from the underlying dynamic string property. If the property is undefined, this method
     * returns the default list value.   
     */
    public List<T> get() {
        return values;
    }
    
    @Override
    public List<T> getValue() {
        return get();
    }
    
    @Override
    public List<T> getDefaultValue() {
        return defaultValues;
    }

    private List<String> split(String value) {        
        return Lists.newArrayList(splitter.split(Strings.nullToEmpty(value)));
    }
    
    protected List<T> transform(List<String> stringValues) {
        List<T> list = new ArrayList<T>(stringValues.size());
        for (String s : stringValues) {
            list.add(from(s));
        }
        return Collections.unmodifiableList(list);    
    }
    
    
    protected void load() {
        if (delegate.get() == null) {
            values = defaultValues;
        } else {
            values = transform(split(delegate.get()));
        }
    }

    
Gets the time (in milliseconds past the epoch) when the property
was last set/changed.
/**
     * Gets the time (in milliseconds past the epoch) when the property
     * was last set/changed.
     */
    @Override
    public long getChangedTimestamp() {
        return delegate.getChangedTimestamp();
    }

    
Add the callback to be triggered when the value of the property is changed
/**
     * Add the callback to be triggered when the value of the property is changed
     *
     */
    @Override
    public void addCallback(Runnable callback) {
        if (callback != null) {
            delegate.addCallback(callback);
        }
    }

    
Remove all callbacks registered through this instance of property
/**
     * Remove all callbacks registered through this instance of property
     */
    @Override
    public void removeAllCallbacks() {
        delegate.removeAllCallbacks();
    }


    
Construct the generic type from string.
/**
     * Construct the generic type from string.
     * 
     */
    protected abstract T from(String value);
    
    
Getter for the property name
/**
     * Getter for the property name
     */
    @Override
    public String getName() {
        return delegate.getName();
    }
}