diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..c81fb67
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,24 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<phpunit
+    backupGlobals='false'
+    backupStaticAttributes='false'
+    colors='true'
+    convertErrorsToExceptions='true'
+    convertNoticesToExceptions='true'
+    convertWarningsToExceptions='true'
+    processIsolation='false'
+    stopOnFailure='false'>
+
+    <testsuites>
+        <testsuite name='FilePermissionCalculator_FilePermissionCalculator'>
+            <directory>./tests/</directory>
+        </testsuite>
+    </testsuites>
+
+    <filter>
+        <whitelist>
+            <directory>./src/</directory>
+        </whitelist>
+    </filter>
+
+</phpunit>
\ No newline at end of file
diff --git a/src/FilePermissionCalculator.php b/src/FilePermissionCalculator.php
index 169bada..825070a 100644
--- a/src/FilePermissionCalculator.php
+++ b/src/FilePermissionCalculator.php
@@ -7,8 +7,293 @@
  * This source file is subject to the MIT license that is bundled
  * with this source code in the file LICENSE.
  */
+
 namespace GisoStallenberg\FilePermissionCalculator;
 
-class FilePermissionCalculator {
+use InvalidArgumentException;
+
+/**
+ * Class that can convert permission info to various formats.
+ */
+class FilePermissionCalculator
+{
+    /**
+     * The permissions.
+     *
+     * @var int
+     */
+    private $permissions = 0;
+
+    /**
+     * Creates a new file permission calculator.
+     *
+     * @param type $permissions
+     */
+    public function __construct($permissions)
+    {
+        $this->verifyValue($permissions);
+        $this->permissions = (int) $permissions;
+    }
+
+    /**
+     * Make sure the argument is octal, please note that some decimals are also considered octal.
+     *
+     * @param mixed $value
+     *
+     * @return bool
+     *
+     * @throws InvalidArgumentException
+     */
+    private function verifyValue($value)
+    {
+        if (is_string($value)) {
+            throw new InvalidArgumentException('Given value is a string, please use fromOctalString to make sure the value gets set up correctly');
+        }
+
+        return true;
+    }
+
+    /**
+     * The decimal value.
+     *
+     * @return int
+     */
+    public function getMode()
+    {
+        return $this->permissions;
+    }
+
+    /**
+     * The decimal value.
+     *
+     * @return int
+     */
+    public function getDecimal()
+    {
+        return $this->permissions;
+    }
+
+    /**
+     * The octal value as string.
+     *
+     * @return string
+     */
+    public function getOctalString()
+    {
+        return decoct($this->permissions);
+    }
+
+    /**
+     * The string value.
+     *
+     * @return int
+     */
+    public function getString()
+    {
+        return sprintf('%o', $this->permissions);
+    }
+
+    /**
+     * Create a new instance asuming the argument is octal.
+     *
+     * @param octal $octal
+     *
+     * @return FilePermissionCalculator
+     */
+    public static function fromOctal($octal)
+    {
+        return new static($octal);
+    }
+
+    /**
+     * Create a new instance asuming the argument is string representation of an octal.
+     *
+     * @param string $octalString
+     *
+     * @return FilePermissionCalculator
+     */
+    public static function fromOctalString($octalString)
+    {
+        return new static(octdec($octalString));
+    }
+
+    /**
+     * Create a new instance asuming the argument is decimal.
+     *
+     * @param decimal $octal
+     *
+     * @return FilePermissionCalculator
+     */
+    public static function fromDecimal($decimal)
+    {
+        return static::fromOctalString(decoct($decimal));
+    }
+
+    /**
+     * Create a new instance asuming the argument is octal.
+     *
+     * @param octal $octal
+     *
+     * @return FilePermissionCalculator
+     */
+    public static function fromStringRepresentation($permissions)
+    {
+        return new static(static::getModeFromStringRepresentation($permissions));
+    }
+
+    /**
+     * Create a new instance using the permission info from the given file.
+     *
+     * @param string $file
+     *
+     * @return FilePermissionCalculator
+     */
+    public static function fromFile($file)
+    {
+        return new static(fileperms($file));
+    }
+
+    /**
+     * Create a string representation of the permissions.
+     *
+     * @return FilePermissionCalculator
+     */
+    public function __toString()
+    {
+        return static::getStringRepresentation($this->permissions);
+    }
+
+    /**
+     * Gives a string representation of the permissions.
+     *
+     * See "Example #2 Display full permissions" on http://php.net/manual/en/function.fileperms.php
+     *
+     * @param int $mode
+     *
+     * @return FilePermissionCalculator
+     */
+    public static function getStringRepresentation($mode)
+    {
+        $permissions = '';
+
+        if (($mode & 0xC000) == 0xC000) {
+            $permissions = 's'; // socket
+        } elseif (($mode & 0xA000) == 0xA000) {
+            $permissions = 'l'; // symbolic link
+        } elseif (($mode & 0x8000) == 0x8000) {
+            $permissions = '-'; // regular
+        } elseif (($mode & 0x6000) == 0x6000) {
+            $permissions = 'b'; // block special
+        } elseif (($mode & 0x4000) == 0x4000) {
+            $permissions = 'd'; // directory
+        } elseif (($mode & 0x2000) == 0x2000) {
+            $permissions = 'c'; // character special
+        } elseif (($mode & 0x1000) == 0x1000) {
+            $permissions = 'p'; // FIFO pipe
+        } else {
+            $permissions = 'u'; // unknown
+        }
+
+        // owner
+        $permissions .= (($mode & 0x0100) ? 'r' : '-');
+        $permissions .= (($mode & 0x0080) ? 'w' : '-');
+        $permissions .= (($mode & 0x0040) ?
+                    (($mode & 0x0800) ? 's' : 'x') :
+                    (($mode & 0x0800) ? 'S' : '-'));
+
+        // group
+        $permissions .= (($mode & 0x0020) ? 'r' : '-');
+        $permissions .= (($mode & 0x0010) ? 'w' : '-');
+        $permissions .= (($mode & 0x0008) ?
+                    (($mode & 0x0400) ? 's' : 'x') :
+                    (($mode & 0x0400) ? 'S' : '-'));
+
+        // world
+        $permissions .= (($mode & 0x0004) ? 'r' : '-');
+        $permissions .= (($mode & 0x0002) ? 'w' : '-');
+        $permissions .= (($mode & 0x0001) ?
+                    (($mode & 0x0200) ? 't' : 'x') :
+                    (($mode & 0x0200) ? 'T' : '-'));
+
+        return $permissions;
+    }
+
+    /**
+     * Converts the string representation to a mode.
+     *
+     * See comment of 'paul maybe at squirrel mail org' on http://php.net/manual/en/function.chmod.php
+     *
+     * @param string $permissions
+     *
+     * @return int
+     */
+    public static function getModeFromStringRepresentation($permissions)
+    {
+        if (strlen($permissions) !== 10) {
+            throw new InvalidArgumentException('Please provide a 10 character long string');
+        }
+        $mode = 0;
+
+        if ($permissions[0] == 's') {
+            $mode = 0140000;
+        } elseif ($permissions[0] == 'l') {
+            $mode = 0120000;
+        } elseif ($permissions[0] == '-') {
+            $mode = 0100000;
+        } elseif ($permissions[0] == 'b') {
+            $mode = 060000;
+        } elseif ($permissions[0] == 'd') {
+            $mode = 040000;
+        } elseif ($permissions[0] == 'c') {
+            $mode = 020000;
+        } elseif ($permissions[0] == 'p') {
+            $mode = 010000;
+        } elseif ($permissions[0] == 'u') {
+            $mode = 0;
+        }
+
+        if ($permissions[1] == 'r') {
+            $mode += 0400;
+        }
+        if ($permissions[2] == 'w') {
+            $mode += 0200;
+        }
+        if ($permissions[3] == 'x') {
+            $mode += 0100;
+        } elseif ($permissions[3] == 's') {
+            $mode += 04100;
+        } elseif ($permissions[3] == 'S') {
+            $mode += 04000;
+        }
+
+        if ($permissions[4] == 'r') {
+            $mode += 040;
+        }
+        if ($permissions[5] == 'w') {
+            $mode += 020;
+        }
+        if ($permissions[6] == 'x') {
+            $mode += 010;
+        } elseif ($permissions[6] == 's') {
+            $mode += 02010;
+        } elseif ($permissions[6] == 'S') {
+            $mode += 02000;
+        }
+
+        if ($permissions[7] == 'r') {
+            $mode += 04;
+        }
+        if ($permissions[8] == 'w') {
+            $mode += 02;
+        }
+        if ($permissions[9] == 'x') {
+            $mode += 01;
+        } elseif ($permissions[9] == 't') {
+            $mode += 01001;
+        } elseif ($permissions[9] == 'T') {
+            $mode += 01000;
+        }
 
-}
\ No newline at end of file
+        return $mode;
+    }
+}
diff --git a/tests/FilePermissionCalculatorTest.php b/tests/FilePermissionCalculatorTest.php
new file mode 100644
index 0000000..1ff3b95
--- /dev/null
+++ b/tests/FilePermissionCalculatorTest.php
@@ -0,0 +1,108 @@
+<?php
+
+namespace GisoStallenberg\Test;
+
+use GisoStallenberg\FilePermissionCalculator\FilePermissionCalculator;
+use PHPUnit_Framework_TestCase;
+
+/**
+ * FilePermissionCalculatorTest.
+ *
+ * @author  Giso Stallenberg <gisostallenberg@gmail.com>
+ */
+class FilePermissionCalculatorTest extends PHPUnit_Framework_TestCase
+{
+    /**
+     * Tests instantiation of FilePermissionCalculator.
+     */
+    public function testConstruct()
+    {
+        $this->assertAttributeSame(0777, 'permissions', new FilePermissionCalculator(0777));
+    }
+
+    /**
+     * Tests if construction using a string fails.
+     *
+     * @expectedException InvalidArgumentException
+     */
+    public function testInvalidStringConstruct()
+    {
+        new FilePermissionCalculator('0777');
+    }
+
+    /**
+     * Test if creating from mode string fails with empty string.
+     *
+     * @expectedException InvalidArgumentException
+     */
+    public function testGetModeFromStringRepresentationFailsOnShortArgument()
+    {
+        FilePermissionCalculator::getModeFromStringRepresentation('');
+    }
+
+    /**
+     * Tests if the getters return expected results.
+     *
+     * @dataProvider provideGettersAndResults
+     */
+    public function testGetterResults($initial, $getter, $expected)
+    {
+        if ($initial instanceof FilePermissionCalculator) {
+            $filepermissioncalculator = $initial;
+        } else {
+            $filepermissioncalculator = new FilePermissionCalculator($initial);
+        }
+
+        $this->assertEquals($expected, $filepermissioncalculator->$getter());
+    }
+
+    /**
+     * Tests if the creators work.
+     *
+     * @dataProvider provideCreators
+     */
+    public function testCreators($creator, $argument, $expected, $getter = 'getMode')
+    {
+        $filepermissioncalculator = FilePermissionCalculator::$creator($argument);
+        $this->assertEquals($expected, $filepermissioncalculator->$getter());
+    }
+
+    /**
+     * Provide data for getters test.
+     *
+     * @return array
+     */
+    public function provideGettersAndResults()
+    {
+        return array(
+            array(0777, 'getMode', 511),
+            array(0777, 'getDecimal', 511),
+            array(0777, 'getString', 777),
+            array(0777, 'getOctalString', '777'),
+            array(0100777, 'getOctalString', '100777'),
+        );
+    }
+
+    /**
+     * Returns an array with creators that make a FilePermissionCalculator and the expected results.
+     *
+     * @return array
+     */
+    public function provideCreators()
+    {
+        return array(
+            array('fromOctal', 0777, 0777),
+            array('fromOctal', 0000, 0),
+            array('fromOctalString', '0777', 0777),
+            array('fromOctalString', 777, 0777),
+            array('fromDecimal', 33279, 0100777),
+            array('fromDecimal', '33279', 0100777),
+            array('fromDecimal', 33279.0, 0100777),
+            array('fromStringRepresentation', '-rwxrwxrwx', 0100777),
+            array('fromStringRepresentation', 'urwxrwxrwx', 0777),
+            array('fromStringRepresentation', '----------', 0100000),
+            array('fromStringRepresentation', 'u---------', 0),
+            array('fromFile', 'tests/Resources/writable-regular', 0100444),
+        );
+    }
+}
diff --git a/tests/Resources/writable-regular b/tests/Resources/writable-regular
new file mode 100644
index 0000000..e69de29