$o1 = array_pop($stack);
$r = apply_operator($t, $o1, null);
array_push($stack, $r);
} else {
// binary
$o1 = array_pop($stack);
$o2 = array_pop($stack);
$r = apply_operator($t, $o1, $o2);
array_push($stack, $r);
}
} else {
// operand
array_push($stack, $t);
}
}
if (count($stack) != 1) {
die("invalid token array");
}
return $stack[0];
}
// $input = array("A", "and", "B", "or", "C", "and", "(", "D", "or", "F", "or", "not", "G", ")");
$input = array("false", "and", "true", "or", "true", "and", "(", "false", "or", "false", "or", "not", "true", ")");
// math or math or math and other and other
$input = array("(", "true", "or", "false", "or", "false", ")", "and", "true", "and", "true");
$input = array("true", "and", "false");
$tokens = shunting_yard($input);
$result = eval_rpn($tokens);
/*foreach($input as $t)
echo $t." ";
echo "==> ".($result ? "true" : "false")."\n";
*/
function evalFullPrereq($token, $studentId, $courseId)
{
$result = "false";
try {
if (!validateToken($token, $studentId)) {
return 403;
}
$conn = new PDO(DBCONNECTSTRING, DBUSER, DBPASSWORD);
$sql = 'SELECT expression FROM prereqs WHERE prereqs.courseId=:courseId';
$stmt = $conn->prepare($sql);
$stmt->bindParam(':courseId', $courseId);
$stmt->execute();
$prereq = $stmt->fetch();
//echo "pcount: ".$stmt->rowCount()."<br />";
if ($stmt->rowCount() <= 0) {
//double check no prereqs
//echo "courseId: ".$courseId;
$sql = 'SELECT prereqs FROM courses WHERE courses.id=:courseId';
$stmt = $conn->prepare($sql);
$stmt->bindParam(':courseId', $courseId);
$stmt->execute();
$course = $stmt->fetch();
if ($stmt->rowCount() <= 0) {
//echo "if";
return 404;
//course not found
} else {
if ($course['prereqs'] == 0) {
//echo "else";
return true;
//no prereqs
}
}
//echo "neither";
}
//echo "expression: ".$prereq['expression']." ;";
$tokens = explode(" ", $prereq['expression']);
$evaledTokens = [];
foreach ($tokens as $token) {
//echo "<p>token:".$token;
if (is_numeric($token)) {
$eval = evalSinglePrereq($token, $studentId, $token);
// echo "=>".$eval;
$evaledTokens[] = $eval;
} else {
$evaledTokens[] = $token;
}
// echo "</p>";
}
//end foreach token
//echo "<p>";
foreach ($evaledTokens as $t) {
//echo $t." ";
}
// echo "</p>";
//send boolean expression to shunting yard function
$input = shunting_yard($evaledTokens);
$result = eval_rpn($input);
foreach ($evaledTokens as $t) {
//echo $t." ";
//echo "==> ".($result ? "true" : "false")."\n";
$sql = "";
}
$stmt = null;
/*
if($prereq['type'] == 2) // grade of X or above in X course
{
//Did student take course and make grade?
$sql = 'SELECT id, grade from course_records WHERE studentId=:stuId AND courseId=:courseId AND type=1';
$stmt = $conn->prepare($sql);
$stmt->bindParam(':stuId',$studentId);
$stmt->bindParam(':courseId',$prereq['courseId']);
$stmt->execute();
$taken = $stmt->fetchAll();
$count=0;
$count = $stmt->rowCount();
echo "taken: ".$count."<br />";
$meetsPrereq = false;
if($count>0) {
foreach($taken as $c) {
if($c['grade'] >= $prereq['minGrade'])
$meetsPrereq = true;
}
}
$result = $meetsPrereq? "true":"false";
echo "<p> Meets Prereq? ".$result."</p>";
}//end if type=2
else if($prereq['type'] == 3) // at least X hours in X group
{
//TODO
}
*/
} catch (PDOException $e) {
//echo $sql . "<br>" . $e->getMessage();
return 500;
}
$conn = null;
return $result;
}
public function calc($expression)
{
return calc_rpn(shunting_yard($expression));
}
