/*
 * Copyright (c) 2002-2011 JGoodies Karsten Lentzsch. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  o Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 *
 *  o Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 *  o Neither the name of JGoodies Karsten Lentzsch nor the names of
 *    its contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
 * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package com.jgoodies.binding.value;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

import javax.swing.Timer;

/**
 * A ValueModel that deferres updates and read-access for a specified delay.
 * Useful to coalesce frequent changes. For example if a heavy computation
 * shall be performed only for a "stable" selection after a series of
 * quick selection changes.<p>
 *
 * Wraps a given subject ValueModel and observes subject value changes
 * and forwards them to listeners of this model after a delay. If the subject
 * value changes, a Swing Timer is used to delay the change notification.
 * A previously started timer - if any - will be stopped before.
 * Reading this model's value returns:
 *  a) the subject value if there's no pending update, or
 *  b) this model's old value that will be updated after the delay.
 * If a value is set to this model, it immediately updates the subject value.<p>
 *
 * TODO: Describe how and when listeners get notified about the delayed change.<p>
 *
 * TODO: Write about the recommended delay time - above the double-click time
 * and somewhere below a second, e.g. 100ms to 200ms.<p>
 *
 * TODO: Write about a slightly different commit handling. The current
 * implementation defers the commit until the value is stable for the
 * specified delay; it's a DelayUntilStableForXXXmsValueModel. Another
 * feature is to delay for a specified time but ensure that some commits
 * and change notifications happen. The latter is a CoalescingWriteValueModel.<p>
 *
 * TODO: Summarize the differences between the DelayedReadValueModel, the
 * DelayedWriteValueModel, and the DelayedPropertyChangeHandler.
 *
 * @author Karsten Lentzsch
 * @version $Revision: 1.14 $
 *
 * @see javax.swing.Timer
 *
 * @since 1.1
 */
public final class DelayedReadValueModel extends AbstractValueModel {

    /**
     * Refers to the underlying subject ValueModel.
     */
    private final ValueModel subject;

    /**
     * The Timer used to perform the delayed commit.
     */
    private final Timer timer;

    /**
     * If {@code true} all pending updates will be coalesced.
     * In other words, an update will be fired if no updates
     * have been received for this model's delay.
     */
    private boolean coalesce;

    /**
     * Holds this model's old value that is returned in {@code getValue}
     * during a pending change.  most recent old value. It is set in
     * {@code #fireDelayedValueChange}.
     */
    private Object oldValue;

    /**
     * Holds the most recent pending PropertyChangeEvent as provided
     * from the subject change notification that this model deferres.
     * {@code #fireDelayedValueChange}.
     */
    private PropertyChangeEvent pendingEvt;


    // Instance Creation ******************************************************

    /**
     * Constructs a DelayedReadValueModel for the given subject ValueModel
     * and the specified Timer delay in milliseconds with coalescing disabled.
     *
     * @param subject   the underlying (or wrapped) ValueModel
     * @param delay     the milliseconds to wait before a change
     *     shall be committed
     *
     * @throws IllegalArgumentException if the delay is negative
     */
    public DelayedReadValueModel(ValueModel subject, int delay) {
        this(subject, delay, false);
    }


    /**
     * Constructs a DelayedReadValueModel for the given subject ValueModel
     * and the specified Timer delay in milliseconds using the given
     * coalesce mode.
     *
     * @param subject   the underlying (or wrapped) ValueModel
     * @param delay     the milliseconds to wait before a change
     *     shall be committed
     * @param coalesce  {@code true} to coalesce all pending changes,
     *     {@code false} to fire changes with the delay when an update
     *     has been received
     *
     * @throws IllegalArgumentException if the delay is negative
     *
     * @see #setCoalesce(boolean)
     */
    public DelayedReadValueModel(ValueModel subject, int delay, boolean coalesce) {
        this.subject = subject;
        this.coalesce = coalesce;
        this.timer = new Timer(delay, new ValueUpdateListener());
        timer.setRepeats(false);
        subject.addValueChangeListener(new SubjectValueChangeHandler());
        oldValue = subject.getValue();
    }


    // ValueModel Implementation ******************************************

    /**
     * Returns the subject's value or in case of a pending commit,
     * the pending new value.
     *
     * @return the subject's current or future value.
     */
    public Object getValue() {
        return isPending()
            ? oldValue
            : subject.getValue();
    }


    /**
     * Sets the given new value immediately as the subject's new value.
     * Note that change notifications from the subject are deferred
     * by this model. Therefore listeners registered with this model
     * will be notified after this model's delay.
     *
     * @param newValue   the value to set
     */
    public void setValue(Object newValue) {
        subject.setValue(newValue);
    }


    // Accessors **************************************************************

    /**
     * Returns the delay, in milliseconds, that is used to defer value change
     * notifications.
     *
     * @return the delay, in milliseconds, that is used to defer
     *     value change notifications
     *
     * @see #setDelay
     */
    public int getDelay() {
        return timer.getDelay();
    }

    /**
     * Sets the delay, in milliseconds, that is used to defer value change
     * notifications.
     *
     * @param delay   the delay, in milliseconds, that is used to defer
     *     value change notifications
     * @see #getDelay
     */
    public void setDelay(int delay) {
        timer.setInitialDelay(delay);
        timer.setDelay(delay);
    }


    /**
     * Returns if this model coalesces all pending changes or not.
     *
     * @return {@code true} if all pending changes will be coalesced,
     *     {@code false} if pending changes are fired with a delay
     *     when an update has been received.
     *
     * @see #setCoalesce(boolean)
     */
    public boolean isCoalesce() {
        return coalesce;
    }

    /**
     * Sets if this model shall coalesce all pending changes or not.
     * In this case, a change event will be fired first,
     * if no updates have been received for this model's delay.
     * If coalesce is {@code false}, a change event will be fired
     * with this model's delay when an update has been received.<p>
     *
     * The default value is {@code false}.<p>
     *
     * Note that this value is not the #coalesce value
     * of this model's internal Swing timer.
     *
     * @param b {@code true} to coalesce,
     *     {@code false} to fire separate changes
     */
    public void setCoalesce(boolean b) {
        coalesce = b;
    }


    // Misc *******************************************************************

    /**
     * Stops a running timer. Pending changes - if any - are canceled
     * and won't be performed by the {@code ValueUpdateListener}.
     *
     * @since 1.2
     */
    public void stop() {
        timer.stop();
    }


    /**
     * Checks and answers whether this model has one or more pending changes.
     *
     * @return {@code true} if there are pending changes, {@code false} if not.
     *
     * @since 2.0.4
     */
    public boolean isPending() {
        return timer.isRunning();
    }


    /**
     * Sets the given new value after this model's delay.
     * Does nothing if the new value and the latest pending value are the same.
     *
     * @param evt  the PropertyChangeEvent to be fired after this model's delay
     */
    private void fireDelayedValueChange(PropertyChangeEvent evt) {
        pendingEvt = evt;
        if (coalesce) {
            timer.restart();
        } else {
            timer.start();
        }
    }


    // Event Handling *********************************************************

    /**
     * Describes the delayed action to be performed by the timer.
     */
    private final class ValueUpdateListener implements ActionListener {

        /**
         * An ActionEvent has been fired by the Timer after its delay.
         * Fires the pending PropertyChangeEvent, stops the timer,
         * and updates this model's oldValue.<p>
         *
         * TODO: Consider stopping the timer before firing the change,
         * because the change handling may take some time.
         */
        public void actionPerformed(ActionEvent e) {
            fireValueChange(pendingEvt.getOldValue(), pendingEvt.getNewValue(), true);
            stop();
            oldValue = pendingEvt.getNewValue() != null
                ? pendingEvt.getNewValue()
                : subject.getValue();
        }
    }


    /**
     * Forwards value changes in the subject to listeners of this model.
     */
    private final class SubjectValueChangeHandler implements PropertyChangeListener {

        public void propertyChange(PropertyChangeEvent evt) {
            fireDelayedValueChange(evt);
        }
    }

}
