Adds the ability to set the max depth from the composer.json file

Fixes #45

src/Plugin.php

@@ -32,6 +32,8 @@
  */
 class Plugin implements PluginInterface, EventSubscriberInterface
 {
+    const KEY_MAX_DEPTH = 'phpcodesniffer-max-depth';
+
     const MESSAGE_RUNNING_INSTALLER = 'Running PHPCodeSniffer Composer Installer';
     const MESSAGE_NOTHING_TO_INSTALL = 'Nothing to install or update';
     const MESSAGE_NOT_INSTALLED = 'PHPCodeSniffer is not installed';
@@ -277,17 +279,19 @@ private function updateInstalledPaths()
             $searchPaths[] = $this->composer->getInstallationManager()->getInstallPath($package);
         }
 
+        $maxDepth = $this->getMaxDepth();
+        $minDepth = $this->getMinDepth();
+
         $finder = new Finder();
         $finder->files()
             ->ignoreUnreadableDirs()
             ->ignoreVCS(true)
-            ->depth('< 4')
+            ->depth('< ' . $maxDepth)
             ->name('ruleset.xml')
             ->in($searchPaths);
 
-        // Only version 3.x and higher has support for having coding standard in the root of the directory.
-        if ($this->isPHPCodeSnifferInstalled('>= 3.0.0') !== true) {
-            $finder->depth('>= 1');
+        if ($minDepth !== 0) {
+            $finder->depth('>= ' . $minDepth);
         }
 
         // Process each found possible ruleset.
@@ -438,4 +442,51 @@ private function getRelativePath($to)
         }
         return implode('/', $relPath);
     }
+
+    /**
+     * @return string
+     *
+     * @throws \InvalidArgumentException
+     */
+    private function getMaxDepth()
+    {
+        $maxDepth = '4';
+
+        $extra = $this->composer->getPackage()->getExtra();
+
+        if (array_key_exists(self::KEY_MAX_DEPTH, $extra)) {
+            $maxDepth = $extra[self::KEY_MAX_DEPTH];
+            $minDepth = $this->getMinDepth();
+
+            if (
+                is_int($maxDepth) === false     /* Must be an integer */
+                || $maxDepth <= $minDepth       /* Larger than the minimum */
+                || is_float($maxDepth) === true /* Within the boundaries of integer */
+            ) {
+                $message = vsprintf('The value of "%s" (in the composer.json "extra" section) must be an integer larger then %d, %s given.', array(
+                    'key' => self::KEY_MAX_DEPTH,
+                    'min' => $minDepth,
+                    'given' => var_export($maxDepth, true),
+                ));
+
+                throw new \InvalidArgumentException($message);
+            }
+        }
+
+        return $maxDepth;
+    }
+
+    /**
+     * @return int
+     */
+    private function getMinDepth()
+    {
+        $minDepth = 0;
+
+        if ($this->isPHPCodeSnifferInstalled('>= 3.0.0') !== true) {
+            $minDepth = 1;
+        }
+
+        return $minDepth;
+    }
 }