Support for better invalid expression detection and divide by zero (#30)

* Additional validation for bad expressions (*+ for example)

* Removing DivisionByZeroException testing for now

Added more unit tests.

7 files changed, 72 insertions, 1 deletions

diff --git a/src/NXP/Classes/Calculator.php b/src/NXP/Classes/Calculator.php
index bfa7015..253e70c 100644
--- a/src/NXP/Classes/Calculator.php
+++ b/src/NXP/Classes/Calculator.php
@@ -54,7 +54,7 @@ class Calculator
             }
         }
         $result = array_pop($stack);
-        if (!empty($stack)) {
+        if ($result === null || ! empty($stack)) {
             throw new IncorrectExpressionException();
         }
 
diff --git a/src/NXP/Classes/Token/TokenDegree.php b/src/NXP/Classes/Token/TokenDegree.php
index c31b66e..3eec23d 100644
--- a/src/NXP/Classes/Token/TokenDegree.php
+++ b/src/NXP/Classes/Token/TokenDegree.php
@@ -10,6 +10,8 @@
 
 namespace NXP\Classes\Token;
 
+use NXP\Exception\IncorrectExpressionException;
+
 /**
 * @author Alexander Kiryukhin <alexander@symdev.org>
 */
@@ -41,12 +43,20 @@ class TokenDegree extends AbstractOperator
 
     /**
      * @param InterfaceToken[] $stack
+     *
      * @return TokenNumber
+     *
+     * @throws \NXP\Exception\IncorrectExpressionException
      */
     public function execute(&$stack)
     {
         $op2 = array_pop($stack);
         $op1 = array_pop($stack);
+
+        if ($op1 === null || $op2 === null) {
+            throw new IncorrectExpressionException("Power operator requires two operators");
+        }
+
         $result = $op1->getValue() ** $op2->getValue();
 
         return new TokenNumber($result);
diff --git a/src/NXP/Classes/Token/TokenDivision.php b/src/NXP/Classes/Token/TokenDivision.php
index f1c35ff..5bbc35e 100644
--- a/src/NXP/Classes/Token/TokenDivision.php
+++ b/src/NXP/Classes/Token/TokenDivision.php
@@ -10,6 +10,9 @@
 
 namespace NXP\Classes\Token;
 
+use NXP\Exception\IncorrectExpressionException;
+use NXP\Exception\DivisionByZeroException;
+
 /**
 * @author Alexander Kiryukhin <alexander@symdev.org>
 */
@@ -41,12 +44,21 @@ class TokenDivision extends AbstractOperator
 
     /**
      * @param InterfaceToken[] $stack
+     *
      * @return $this
+     *
+     * @throws \NXP\Exception\IncorrectExpressionException
+     * @throws \NXP\Exception\DivisionByZeroException
      */
     public function execute(&$stack)
     {
         $op2 = array_pop($stack);
         $op1 = array_pop($stack);
+
+        if ($op1 === null || $op2 === null) {
+            throw new IncorrectExpressionException("Division requires two operators");
+        }
+
         $result = $op2->getValue() != 0 ? $op1->getValue() / $op2->getValue() : 0;
 
         return new TokenNumber($result);
diff --git a/src/NXP/Classes/Token/TokenMinus.php b/src/NXP/Classes/Token/TokenMinus.php
index 0463d4c..566c950 100644
--- a/src/NXP/Classes/Token/TokenMinus.php
+++ b/src/NXP/Classes/Token/TokenMinus.php
@@ -10,6 +10,8 @@
 
 namespace NXP\Classes\Token;
 
+use NXP\Exception\IncorrectExpressionException;
+
 /**
 * @author Alexander Kiryukhin <alexander@symdev.org>
 */
@@ -41,12 +43,20 @@ class TokenMinus extends AbstractOperator
 
     /**
      * @param InterfaceToken[] $stack
+     *
      * @return $this
+     *
+     * @throws \NXP\Exception\IncorrectExpressionException
      */
     public function execute(&$stack)
     {
         $op2 = array_pop($stack);
         $op1 = array_pop($stack);
+
+        if ($op1 === null || $op2 === null) {
+            throw new IncorrectExpressionException("Subtraction requires two operators");
+        }
+
         $result = $op1->getValue() - $op2->getValue();
 
         return new TokenNumber($result);
diff --git a/src/NXP/Classes/Token/TokenMultiply.php b/src/NXP/Classes/Token/TokenMultiply.php
index e6fd960..8b173b9 100644
--- a/src/NXP/Classes/Token/TokenMultiply.php
+++ b/src/NXP/Classes/Token/TokenMultiply.php
@@ -10,6 +10,8 @@
 
 namespace NXP\Classes\Token;
 
+use NXP\Exception\IncorrectExpressionException;
+
 /**
 * @author Alexander Kiryukhin <alexander@symdev.org>
 */
@@ -41,12 +43,20 @@ class TokenMultiply extends AbstractOperator
 
     /**
      * @param InterfaceToken[] $stack
+     *
      * @return $this
+     *
+     * @throws \NXP\Exception\IncorrectExpressionException
      */
     public function execute(&$stack)
     {
         $op2 = array_pop($stack);
         $op1 = array_pop($stack);
+
+        if ($op1 === null || $op2 === null) {
+            throw new IncorrectExpressionException("Multiplication requires two operators");
+        }
+
         $result = $op1->getValue() * $op2->getValue();
 
         return new TokenNumber($result);
diff --git a/src/NXP/Classes/Token/TokenPlus.php b/src/NXP/Classes/Token/TokenPlus.php
index f9562e7..fe5a1d6 100644
--- a/src/NXP/Classes/Token/TokenPlus.php
+++ b/src/NXP/Classes/Token/TokenPlus.php
@@ -10,6 +10,8 @@
 
 namespace NXP\Classes\Token;
 
+use NXP\Exception\IncorrectExpressionException;
+
 /**
 * @author Alexander Kiryukhin <alexander@symdev.org>
 */
@@ -41,12 +43,20 @@ class TokenPlus extends AbstractOperator
 
     /**
      * @param InterfaceToken[] $stack
+     *
      * @return $this
+     *
+     * @throws \NXP\Exception\IncorrectExpressionException
      */
     public function execute(&$stack)
     {
         $op2 = array_pop($stack);
         $op1 = array_pop($stack);
+
+        if ($op1 === null || $op2 === null) {
+            throw new IncorrectExpressionException("Addition requires two operators");
+        }
+
         $result = $op1->getValue() + $op2->getValue();
 
         return new TokenNumber($result);
diff --git a/src/NXP/Exception/DivisionByZeroException.php b/src/NXP/Exception/DivisionByZeroException.php
new file mode 100644
index 0000000..3a9a978
--- /dev/null
+++ b/src/NXP/Exception/DivisionByZeroException.php
@@ -0,0 +1,19 @@
+<?php
+
+/**
+ * This file is part of the MathExecutor package
+ *
+ * (c) Alexander Kiryukhin
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code
+ */
+
+namespace NXP\Exception;
+
+/**
+ * @author Vitaliy Zhuk <zhuk2205@gmail.com>
+ */
+class DivisionByZeroException extends MathExecutorException
+{
+}