Parse equality string and test equality expression

test-eq-expression.php

<?php

// does not consider &&, ||, XOR, OR, AND operator, ternary operators for now.
$var_a = 100;
$var_b = 100;
$var_c = 110;
$var_d = (double) 100;
$var_e = "100";
$var_f = false;
$symbol_table = compact("var_a", "var_b", "var_c", "var_d", "var_e", "var_f");

echo "'\$var_d == \$var_e' is " . (test_eq_expression('$var_d == $var_e', $symbol_table) == true ? "true" : "false").PHP_EOL;
echo "'\$var_c != \$var_e' is " . (test_eq_expression('$var_c != $var_e', $symbol_table) == true ? "true" : "false").PHP_EOL;
echo "'\$var_b === \$var_e' is " . (test_eq_expression('$var_b === $var_e', $symbol_table) == true ? "true" : "false").PHP_EOL;
echo "'\$var_a =< \$var_e' is " . (test_eq_expression('$var_a =< $var_e', $symbol_table) == true ? "true" : "false").PHP_EOL;
echo "'\$var_a == \$var_b' is " . (test_eq_expression('$var_a == $var_b', $symbol_table) == true ? "true" : "false").PHP_EOL;
echo "'!\$var_f' is " . (test_eq_expression('!$var_f', $symbol_table) == true ? "true" : "false").PHP_EOL;
echo "'!\$var_e' is " . (test_eq_expression('!$var_e', $symbol_table) == true ? "true" : "false").PHP_EOL;
echo "'\$var_f' is " . (test_eq_expression('$var_f', $symbol_table) == true ? "true" : "false").PHP_EOL;
echo "'\$var_e' is " . (test_eq_expression('$var_e', $symbol_table) == true ? "true" : "false").PHP_EOL;

function test_eq_expression($expression, $symbol_table = []) {
  $tokens = token_get_all("<?php $expression ?>");
  if(is_array($tokens)) {
    $fields = [];
    foreach($tokens as $token) {
      if(isset($token[1])) {
        $_ = trim($token[1]);
      }
      else if(is_string($token)){
        $_ = trim($token);
      }
      if(!empty($_) and $_ !== "<?php" and $_ !== "?>") {
        $fields[] = $_; 
      }
    }
    
    if(count($fields) == 1) {
      $operator = "unary";
      $param1 = str_replace("\$", "", $fields[0]);  
    }
    else if(count($fields) == 2) {
      if($fields[0]  == "!") {
        $param1 = str_replace("\$", "", $fields[1]);  
        $operator = $fields[0]; 
      }
    }
    else if(count($fields) == 3) {
      if(in_array($fields[1], ["==", "===", "!=", "!==", "<=", ">=", ">", "<"])) {
        $param1 = str_replace("\$", "", $fields[0]);  
        $param2 = str_replace("\$", "", $fields[2]);
        $operator = $fields[1]; 
      }
    }
    
    switch($operator):
      case "unary":
        return $symbol_table[$param1] ? true : false;
      case "!":
        return !$symbol_table[$param1];
      case "==":
        return $symbol_table[$param1] == $symbol_table[$param2];
        break;
      case "===":
        return $symbol_table[$param1] === $symbol_table[$param2];
        break;
      case "!=":
        return $symbol_table[$param1] != $symbol_table[$param2];
        break;
      case "!==":
        return $symbol_table[$param1] !== $symbol_table[$param2];
        break;
      case "<=":
        return $symbol_table[$param1] <= $symbol_table[$param2];
        break;
      case ">=":
        return $symbol_table[$param1] >= $symbol_table[$param2];
        break;
      case ">":
        return $symbol_table[$param1] > $symbol_table[$param2];
        break;
      case "<":
        return $symbol_table[$param1] < $symbol_table[$param2];
       break;
     endswitch;
  }
}