Task Object, Coordination & Chain of Responsibility Design pattern

Overview.txt

Overview: 
This was an example I have given to my co-developer who was doing some Task/Coodinator type of code. Hope this is helpful to many other developers out there. 

Note that the example only supports one-to-one dependency between TaskObject instance. The TaskAbstract class can be easily modified to support 1-to-many dependency.

For simpicity, I have combined all three classes in this single gist:
  1. TaskAbstract
  2. TaskObject        (extends TaskAbstract) 
  3. TaskCoordinator  (extends TaskAbstract)

The TaskCoordinator class shows an example that resembles the following dependency:

    1. A $queue contains multiple TaskObject instances
    2. TaskObject."Raul" is dependent on TaskObject."Mark"
    3. TaskObject."Mark" is dependent on TaskObject."Tim"
    4. TaskObject."Faustino" is independent.

       ```php
         $queue[] = new TaskObject("Raul");
         $queue[] = new TaskObject("Mark");
         $queue[] = new TaskObject("Tim");
         $queue[] = new TaskObject("Faustino");

         $queue[0]->setDependency($queue[1]);
         $queue[1]->setDependency($queue[2]);
       ```

      [Raul] -> [Mark] -> [Tim]   [Faustino]
        ^                               ^ 
        |                               |
        |                               |
      [Coordinator]                     |
                 .............       [Coordinator]                


The output is:

   Hello! I'm task: Tim
   Hello! I'm task: Mark
   Hello! I'm task: Raul
   Hello! I'm task: Faustino

    

TestTaskCoord.php

<?php

abstract class TaskAbstract {

    const STATUS_READY = 1;
    const STATUS_DONE  = 2;
     
    protected $dependency;
    protected $status;

    abstract public function run($caller);
    public function getStatus() { 
        return $this->status;
    }

    public function setDependency(TaskAbstract $task) {
       $this->dependency = $task;
    }

}


class TaskObject extends TaskAbstract {

    private $taskName = "";

    public function __construct($taskName) {
        $this->taskName = $taskName;
        $this->status = self::STATUS_READY;       
    }
     
    public function run($caller) {
	if ($this->status == self::STATUS_DONE) {
	    return true;
        }

        if ($this->status != self::STATUS_READY) {
	    return false;
        }

        //run dependency if available
        if (!empty($this->dependency)) {
            $this->dependency->run($this);
        }

        echo "Hello! I'm task: {$this->taskName} \n";
        $this->status = self::STATUS_DONE;
    }

}


class TaskCoordinator  extends TaskAbstract {

     public function run( $caller) {
	
         $queue = array();
         $queue[] = new TaskObject("Raul");
         $queue[] = new TaskObject("Mark");
         $queue[] = new TaskObject("Tim");
         $queue[] = new TaskObject("Faustino");

         $queue[0]->setDependency($queue[1]);
         $queue[1]->setDependency($queue[2]);

/*
         $queue[0]->run($this);
         $queue[3]->run($this);

         $queue[3]->run($this);
*/
	foreach ($queue as $q) {
	    $q->run($this);
        }
     }
    
}



$coordinator = new TaskCoordinator();
$coordinator->run(null);

?>