package foobar.util;

import java.util.Calendar;

/**
 * A Timer class that can be extended to invoke an action after a specified
 * number of seconds. It can optionally be configured to synchronize the timer 
 * to the system clock.
 */
public class Timer {

    // Specifies the interval (in seconds) at which the timer should run
    // (The default interval is 30 seconds)
    public attribute interval: Integer;

    // Specifies whether the timer should be synchronized to the system clock.
    // This is useful when creating a timer that fires every minute on the 
    // minute, every hour on the hour etc.
    public attribute synchronize: Boolean;

    // Controls whether the timer is running or not. Setting it to true starts 
    // the timer, and setting this attribute to false terminates the timer.
    public attribute active: Boolean;
    
    // A user configurable action that is invoked when the specified interval
    // expires. This operation must be implemented in the class that extends
    // this Timer class
    public operation action();

    // An internal counter used to synchronize this timer with the system clock
    private attribute countdown: Integer;

    // An internal attribute whose value changes everytime the specified
    // interval expires.
    private attribute tick: Integer;

    ...
}

attribute Timer.interval = 30;
attribute Timer.countdown = 0;

// Change the value of tick every time the specified interval expires. During
// synchronization, the value of tick is changed every second until the
// countdown is completed.
attribute Timer.tick = bind
        if active and synchronize
        then [1..2] dur 2000 linear
            while synchronize and active
            continue if true
        else if active
        then [3..4] dur 2*interval*1000 linear
            while active
            continue if true
        else 0;

// Invoke the user-specified action when the interval expires. During
// synchronization, the action is invoked only when the timer is synchronized
// with the clock.
trigger on Timer.tick = value
{
    if (active) {
        if (synchronize) {
            if (--countdown == 0) {
                synchronize = false;
                action();
            }
        } else {
            action();
        }
    }
}

// When the timer is enabled, determine the number of seconds to the next 
// minute and use this value to synchronize (if that attribute is set to true)
// the timer with the system clock
trigger on Timer.active = value {
    if (value) {
        var d: Calendar = Calendar.getInstance();
        countdown = d.get(Calendar.SECOND);
        if (countdown > 0) {
            countdown = 60 - countdown;
        }
    }
}