diff --git a/src/Composer/Downloader/DownloaderInterface.php b/src/Composer/Downloader/DownloaderInterface.php
index d399ebf88..4416ac46e 100644
--- a/src/Composer/Downloader/DownloaderInterface.php
+++ b/src/Composer/Downloader/DownloaderInterface.php
@@ -20,4 +20,5 @@ use Composer\Package\PackageInterface;
 interface DownloaderInterface
 {
     function download(PackageInterface $package, $path, $url, $checksum = null);
+    function isDownloaded(PackageInterface $package, $path);
 }
diff --git a/src/Composer/Downloader/GitDownloader.php b/src/Composer/Downloader/GitDownloader.php
index 90fa49baa..bb22bc0be 100644
--- a/src/Composer/Downloader/GitDownloader.php
+++ b/src/Composer/Downloader/GitDownloader.php
@@ -28,18 +28,17 @@ class GitDownloader implements DownloaderInterface
 
     public function download(PackageInterface $package, $path, $url, $checksum = null)
     {
-        if (!is_dir($path)) {
-            if (file_exists($path)) {
-                throw new \UnexpectedValueException($path.' exists and is not a directory.');
-            }
-            if (!mkdir($path, 0777, true)) {
-                throw new \UnexpectedValueException($path.' does not exist and could not be created.');
-            }
-        }
         if ($this->clone) {
             system('git clone '.escapeshellarg($url).' -b master '.escapeshellarg($path.'/'.$package->getName()));
         } else {
             system('git archive --format=tar --prefix='.escapeshellarg($package->getName()).' --remote='.escapeshellarg($url).' master | tar -xf -');
         }
     }
+
+    public function isDownloaded(PackageInterface $package, $path)
+    {
+        $targetPath = $path . '/' . $package->getName();
+
+        return is_dir($targetPath);
+    }
 }
diff --git a/src/Composer/Downloader/PearDownloader.php b/src/Composer/Downloader/PearDownloader.php
index 0f4c86289..c93519b1c 100644
--- a/src/Composer/Downloader/PearDownloader.php
+++ b/src/Composer/Downloader/PearDownloader.php
@@ -66,4 +66,11 @@ class PearDownloader implements DownloaderInterface
         }
         chdir($cwd);
     }
+
+    public function isDownloaded(PackageInterface $package, $path)
+    {
+        $targetPath = $path . '/' . $package->getName();
+
+        return is_dir($targetPath);
+    }
 }
diff --git a/src/Composer/Downloader/ZipDownloader.php b/src/Composer/Downloader/ZipDownloader.php
index 94a7eac0e..098ba151a 100644
--- a/src/Composer/Downloader/ZipDownloader.php
+++ b/src/Composer/Downloader/ZipDownloader.php
@@ -73,4 +73,11 @@ class ZipDownloader implements DownloaderInterface
             throw new \UnexpectedValueException($zipName.' is not a valid zip archive, got error code '.$retval);
         }
     }
+
+    public function isDownloaded(PackageInterface $package, $path)
+    {
+        $targetPath = $path . '/' . $package->getName();
+
+        return is_dir($targetPath);
+    }
 }
diff --git a/src/Composer/Installer/LibraryInstaller.php b/src/Composer/Installer/LibraryInstaller.php
index b2a954ca6..e45aa6586 100644
--- a/src/Composer/Installer/LibraryInstaller.php
+++ b/src/Composer/Installer/LibraryInstaller.php
@@ -18,15 +18,18 @@ use Composer\Composer;
 
 /**
  * @author Jordi Boggiano <j.boggiano@seld.be>
+ * @author Konstantin Kudryashov <ever.zet@gmail.com>
  */
 class LibraryInstaller implements InstallerInterface
 {
     private $dir;
     private $composer;
+    private $preferSource;
 
-    public function __construct($dir = 'vendor')
+    public function __construct($dir = 'vendor', $preferSource = false)
     {
         $this->dir = $dir;
+        $this->preferSource = $preferSource;
     }
 
     public function setComposer(Composer $composer)
@@ -36,39 +39,52 @@ class LibraryInstaller implements InstallerInterface
 
     public function install(PackageInterface $package)
     {
-        if ($package->getDistType()) {
+        if (!is_dir($this->dir)) {
+            if (file_exists($this->dir)) {
+                throw new \UnexpectedValueException($this->dir.' exists and is not a directory.');
+            }
+            if (!mkdir($this->dir, 0777, true)) {
+                throw new \UnexpectedValueException($this->path.' does not exist and could not be created.');
+            }
+        }
 
-            $this->composer->getDownloader($package->getDistType())->download(
+        if (!($this->preferSource && $package->getSourceType()) && $package->getDistType()) {
+            $downloader = $this->composer->getDownloader($package->getDistType());
+
+            return $downloader->download(
                 $package, $this->dir, $package->getDistUrl(), $package->getDistSha1Checksum()
             );
+        }
 
-        } elseif ($package->getSourceType()) {
+        if ($package->getSourceType()) {
+            $downloader = $this->composer->getDownloader($package->getSourceType());
 
-            $this->composer->getDownloader($package->getSourceType())->download(
+            return $downloader->download(
                 $package, $this->dir, $package->getSourceUrl()
             );
-
-        } else {
-            throw new \InvalidArgumentException(
-                'Type must be one of (dist, source), '.$type.' given.'
-            );
         }
 
-        return true;
+        throw new \InvalidArgumentException('Package should have dist or source specified');
     }
 
     public function isInstalled(PackageInterface $package)
     {
-        // TODO: implement installation check
-    }
+        if ($package->getSourceType()) {
+            $downloader = $this->composer->getDownloader($package->getSourceType());
 
-    public function update(PackageInterface $package)
-    {
-        // TODO: implement package update
-    }
+            if ($downloader->isDownloaded($package, $this->dir)) {
+                return true;
+            }
+        }
 
-    public function remove(PackageInterface $package)
-    {
-        // TODO: implement package removal
+        if ($package->getDistType()) {
+            $downloader = $this->composer->getDownloader($package->getDistType());
+
+            if ($downloader->isDownloaded($package, $this->dir)) {
+                return true;
+            }
+        }
+
+        return false;
     }
 }