<?php
// Survey database interface class as intermediate for storing data from the site to the RDF database 
require_once 'rdfConstants.php';
// Include RAP Library to write RDF files
include(RDFAPI_INCLUDE_DIR . "RDFAPI.php");

/**
 * Description of Answer
 *
 * @author jkraaijeveld
 */
class Answer extends ResearchToolObject {
	public static $filename = 'data/results/answers.rdf';

    public $question;
	public $values;
    
    /**
     * Constructor for an Answer object
     * @param type $uid : The uid of the Answer object.
     * @param type $question : The Question object this Answer answers.
     * @param type $values : An array of strings, containing the answers.
     */
    public function __construct($uid = null, $question = null, $values = null) {
      if(!isset($uid))
      {
            $uid = md5(uniqid(rand(), true));
      }
      $this->uid = $uid;
      $this->question = $question;
      $this->values = $values;
	}
	
	/**
	 * function evaluate()
	 * Evaluates the references and fills in the objects for them instead.
	 */
	public function evaluate()
	{
		if(is_string($this->question))
		{
			$result = Question::get(array("code" => $this->question));
			if(!isset($result[0]))
				return false;
			$this->question = $result[0];
		}
		return true;
	}


	/**
	 * function get()
	 * @param type $arguments: An array having one or more of the following elements:
	 * 'uid', 'question', 'values'.
	 */
    public static function get($arguments)
	{
		$model = ResearchToolObject::load(Answer::$filename);
		//Create the querystring
		$querystring = '
			PREFIX predicates: <' . SURVEYTOOL_PREDICATES_NAMESPACE . '>
			PREFIX resources: <' . SURVEYTOOL_RESOURCES_NAMESPACE . '>
			SELECT DISTINCT ?uid, ?question_code
			WHERE
			{
				_answer predicates:resource_type resources:answer;

				predicates:uid ?uid ;
				predicates:question_code ?question_code ;
				' . ResearchToolObject::createArguments($arguments) . '
			}';

		//Query the model
		$results = $model->sparqlQuery($querystring);	
		//An answer can have multiple values, get all these values for the answer instances found.
		$answers = array();
		if(!empty($results))
		{
			foreach($results as $result)
			{
				$answers[] = new Answer($result['?uid']->label, $result['?question_code']->label, Answer::getValues($model, $result['?uid']->label));
			}
		}
		return $answers;
	}

	/**
	 * function getValues()
	 * @param type $uid : The uid of the Answer for which the values should be gotten.
	 */
	private static function getValues($model, $uid)
	{
		$result = $model->findRegex("[(".$uid.")]", "[(answered)]", null);
		$iterator = $result->getStatementIterator();
		$values = array();
		while($iterator->hasNext())
		{
			$element = $iterator->next();
			$values[] = $element->getLabelObject();
		}
		return $values;
	} 

    /**
	 * function save()
	 * Saves the current object into the database.
     */
    public function save()
    {
		//If evaluation fails, some references are incorrect.
		//We shouldn't save in this case. Instead - let the user know. This function returns false if the evaluation has failed.
		//TODO: Decide how to fix invalid references graciously.
		if(!$this->evaluate()) 
			return false;

		//Ensure the required folder exists.
		if(!is_dir('data/results'))
			mkdir('data/results');
		$model = ResearchToolObject::load(Answer::$filename);

        $resourceAnswer = new Resource(ANSWER.'/'.$this->uid);        
        //Remove the old value stored with the given id
        $model->subtract($model->find($resourceAnswer, null, null));
        
        //Save all the new values
        $resourceAnswerType = new Resource(ANSWER);
        $predicateRType = new Resource(RTYPE);
        $model->add(new Statement($resourceAnswer,$predicateRType,$resourceAnswerType));
        
		$answerId = new Literal($this->uid);
		$predicateId = new Resource(UID);
		$model->add(new Statement($resourceAnswer, $predicateId, $answerId));

		$questionId = new Literal($this->question->uid);
		$predicateQId = new Resource(QCODE);
		$model->add(new Statement($resourceAnswer, $predicateQId, $questionId));

		if(isset($this->values))
		{
			foreach($this->values as $value)
			{
				$answerValue = new Literal($value);
				$predicateAnswer = new Resource(ANSWERED);
				$model->add(new Statement($resourceAnswer, $predicateAnswer, $answerValue));
			}
		}
		$model->saveAs(Answer::$filename, 'rdf');
		return true;
	}
}

?>