/**
* This function actually traverses the tree and generates outcomes.
*
* @param stack_cas_session $questionvars the question varaibles.
* @param stack_options $options
* @param array $answers name => value the student response.
* @param int $seed the random number seed.
* @return stack_potentialresponse_tree_state the result.
*/
public function evaluate_response(stack_cas_session $questionvars, $options, $answers, $seed)
{
if (empty($this->nodes)) {
throw new stack_exception('stack_potentialresponse_tree: evaluate_response ' . 'attempting to traverse an empty tree. Something is wrong here.');
}
$localoptions = clone $options;
$localoptions->set_option('simplify', $this->simplify);
$cascontext = $this->create_cas_context_for_evaluation($questionvars, $localoptions, $answers, $seed);
$results = new stack_potentialresponse_tree_state($this->value, true, 0, 0);
// Traverse the tree.
$nodekey = $this->firstnode;
$visitednodes = array();
while ($nodekey != -1) {
if (!array_key_exists($nodekey, $this->nodes)) {
throw new stack_exception('stack_potentialresponse_tree: ' . 'evaluate_response: attempted to jump to a potential response ' . 'which does not exist in this question. This is a question ' . 'authoring/validation problem.');
}
if (array_key_exists($nodekey, $visitednodes)) {
$results->add_answernote('[PRT-CIRCULARITY]=' . $nodekey);
break;
}
$visitednodes[$nodekey] = true;
$nodekey = $this->nodes[$nodekey]->traverse($results, $nodekey, $cascontext, $localoptions);
if ($results->_errors) {
break;
}
}
// Make sure these are PHP numbers.
$results->_score = $results->_score + 0;
$results->_penalty = $results->_penalty + 0;
// Restrict score to be between 0 and 1.
$results->_score = min(max($results->_score, 0), 1);
// From a strictly logical point of view the 'score' and the 'penalty' are independent.
// Hence, this clause belongs in the question behaviour.
// From a practical point of view, it is confusing/off-putting when testing to see "score=1, penalty=0.1".
// Why does this correct attempt attract a penalty? So, this is a unilateral decision:
// If the score is 1 there is never a penalty.
if ($results->_score > 0.99999995) {
$results->_penalty = 0;
}
if ($results->errors) {
$results->_score = null;
$results->_penalty = null;
}
$results->set_cas_context($cascontext, $seed);
return $results;
}
/**
* Actually execute the test for this node.
*/
public function do_test($nsans, $ntans, $ncasopts, $options, stack_potentialresponse_tree_state $results)
{
if (false === $ncasopts) {
$ncasopts = $this->atoptions;
}
$at = new stack_ans_test_controller($this->answertest, $nsans, $ntans, $options, $ncasopts);
$at->do_test();
$testpassed = $at->get_at_mark();
if ($testpassed) {
$resultbranch = $this->branches[1];
$branchname = 'prtnodetruefeedback';
} else {
$resultbranch = $this->branches[0];
$branchname = 'prtnodefalsefeedback';
}
if ($at->get_at_answernote()) {
$results->add_answernote($at->get_at_answernote());
}
if ($resultbranch['answernote']) {
$results->add_answernote($resultbranch['answernote']);
}
// If the answer test is running in quiet mode we suppress any
// automatically generated feedback from the answertest itself.
if (!$this->quiet && $at->get_at_feedback()) {
$results->add_feedback($at->get_at_feedback());
}
if ($resultbranch['feedback']) {
$results->add_feedback($resultbranch['feedback'], $resultbranch['feedbackformat'], $branchname, $this->nodeid);
}
$results->_valid = $results->_valid && $at->get_at_valid();
$results->_score = $this->update_score($results->_score, $resultbranch);
if ($resultbranch['penalty'] !== '') {
$results->_penalty = $resultbranch['penalty'];
}
$results->_errors .= $at->get_at_errors();
return $resultbranch['nextnode'];
}
