Add support for exponential notation (#5)

Add support for exponential notation

.travis.yml

@@ -8,6 +8,8 @@ php:
   - 5.6
   - 7.0
   - 7.1
+  - 7.2
+  - 7.3
 
 before_script:
   - travis_retry composer install --no-interaction

src/Builder.php

@@ -0,0 +1,101 @@
+<?php
+/**
+ * This file is part of the PrestaShop\Decimal package
+ *
+ * @author    PrestaShop SA <contact@prestashop.com>
+ * @license   https://opensource.org/licenses/MIT MIT License
+ */
+
+namespace PrestaShop\Decimal;
+
+use PrestaShop\Decimal\Number;
+
+
+/**
+ * Builds Number instances
+ */
+class Builder
+{
+
+    /**
+     * Pattern for most numbers
+     */
+    const NUMBER_PATTERN = "/^(?<sign>[-+])?(?<integerPart>\d+)?(?:\.(?<fractionalPart>\d+)(?<exponentPart>[eE](?<exponentSign>[-+])(?<exponent>\d+))?)?$/";
+
+    /**
+     * Pattern for integer numbers in scientific notation (rare but supported by spec)
+     */
+    const INT_EXPONENTIAL_PATTERN = "/^(?<sign>[-+])?(?<integerPart>\d+)(?<exponentPart>[eE](?<exponentSign>[-+])(?<exponent>\d+))$/";
+
+    /**
+     * Builds a Number from a string
+     *
+     * @param string $number
+     *
+     * @return Number
+     */
+    public static function parseNumber($number)
+    {
+        if (!self::itLooksLikeANumber($number, $numberParts)) {
+            throw new \InvalidArgumentException(
+                sprintf('"%s" cannot be interpreted as a number', print_r($number, true))
+            );
+        }
+
+        $integerPart = '';
+        if (array_key_exists('integerPart', $numberParts)) {
+            // extract the integer part and remove leading zeroes
+            $integerPart = ltrim($numberParts['integerPart'], '0');
+        }
+
+        $fractionalPart = '';
+        if (array_key_exists('fractionalPart', $numberParts)) {
+            // extract the fractional part and remove trailing zeroes
+            $fractionalPart = rtrim($numberParts['fractionalPart'], '0');
+        }
+
+        $fractionalDigits = strlen($fractionalPart);
+        $coefficient = $integerPart . $fractionalPart;
+
+        // when coefficient is '0' or a sequence of '0'
+        if ('' === $coefficient) {
+            $coefficient = '0';
+        }
+
+        // when the number has been provided in scientific notation
+        if (array_key_exists('exponentPart', $numberParts)) {
+            $givenExponent = (int) ($numberParts['exponentSign'] . $numberParts['exponent']);
+
+            // we simply add or subtract fractional digits from the given exponent (depending if it's positive or negative)
+            $fractionalDigits -= $givenExponent;
+            if ($fractionalDigits < 0) {
+                // if the resulting fractional digits is negative, it means there is no fractional part anymore
+                // we need to add trailing zeroes as needed
+                $coefficient = str_pad($coefficient, strlen($coefficient) - $fractionalDigits, '0');
+
+                // there's no fractional part anymore
+                $fractionalDigits = 0;
+            }
+        }
+
+        return new Number($numberParts['sign'] . $coefficient, $fractionalDigits);
+    }
+
+    /**
+     * @param string $number
+     * @param array $numberParts
+     *
+     * @return bool
+     */
+    private static function itLooksLikeANumber($number, &$numberParts)
+    {
+        return (
+            strlen((string) $number) > 0
+            && (
+                preg_match(self::NUMBER_PATTERN, $number, $numberParts)
+                || preg_match(self::INT_EXPONENTIAL_PATTERN, $number, $numberParts)
+            )
+        );
+    }
+
+}

src/Number.php

@@ -54,11 +54,11 @@ class Number
      * (string) new Number('123456', 6); // -> '0.123456'
      * ```
      *
-     * Note: exponents are always positive.
+     * Note: decimal positions must always be a positive number.
      *
      * @param string $number Number or coefficient
-     * @param int $exponent [default=null] If provided, the number is considered a coefficient of
-     * the scientific notation.
+     * @param int $exponent [default=null] If provided, the number can be considered as the negative
+     * exponent of the scientific notation, or the number of fractional digits.
      */
     public function __construct($number, $exponent = null)
     {
@@ -69,11 +69,13 @@ public function __construct($number, $exponent = null)
         }
 
         if (null === $exponent) {
-            $this->initFromString($number);
-        } else {
-            $this->initFromScientificNotation($number, $exponent);
+            $decimalNumber = Builder::parseNumber($number);
+            $number = $decimalNumber->getSign() . $decimalNumber->getCoefficient();
+            $exponent = $decimalNumber->getExponent();
         }
 
+        $this->initFromScientificNotation($number, $exponent);
+
         if ('0' === $this->coefficient) {
             // make sure the sign is always positive for zero
             $this->isNegative = false;
@@ -455,39 +457,6 @@ public function toMagnitude($exponent)
         return (new Operation\MagnitudeChange())->compute($this, $exponent);
     }
 
-    /**
-     * Initializes the number using a string
-     *
-     * @param string $number
-     */
-    private function initFromString($number)
-    {
-        if (!preg_match("/^(?<sign>[-+])?(?<integerPart>\d+)(?:\.(?<fractionalPart>\d+))?$/", $number, $parts)) {
-            throw new \InvalidArgumentException(
-                sprintf('"%s" cannot be interpreted as a number', print_r($number, true))
-            );
-        }
-
-        $this->isNegative = ('-' === $parts['sign']);
-
-        // extract the integer part and remove leading zeroes and plus sign
-        $integerPart = ltrim($parts['integerPart'], '0');
-
-        $fractionalPart = '';
-        if (array_key_exists('fractionalPart', $parts)) {
-            // extract the fractional part and remove trailing zeroes
-            $fractionalPart = rtrim($parts['fractionalPart'], '0');
-        }
-
-        $this->exponent = strlen($fractionalPart);
-        $this->coefficient = $integerPart . $fractionalPart;
-
-        // when coefficient is '0' or a sequence of '0'
-        if ('' === $this->coefficient) {
-            $this->coefficient = '0';
-        }
-    }
-
     /**
      * Initializes the number using a coefficient and exponent
      *