diff --git a/app/Services/InvoiceDraft/InvoiceDraft.php b/app/Services/InvoiceDraft/InvoiceDraft.php
index 732ebd2..ee0554e 100644
--- a/app/Services/InvoiceDraft/InvoiceDraft.php
+++ b/app/Services/InvoiceDraft/InvoiceDraft.php
@@ -11,18 +11,58 @@ use App\Entities\Invoices\Invoice;
  */
 class InvoiceDraft
 {
+    /**
+     * Invoice draft items.
+     *
+     * @var array
+     */
     public $items = [];
 
+    /**
+     * Invoice data.
+     *
+     * @var string
+     */
     public $date;
+
+    /**
+     * Invoice notes.
+     *
+     * @var string
+     */
     public $notes;
+
+    /**
+     * Invoice due date.
+     *
+     * @var string
+     */
     public $dueDate;
+
+    /**
+     * Invoice project id from database.
+     *
+     * @var int
+     */
     public $projectId;
 
+    /**
+     * Get item list sort by iten name.
+     *
+     * @return \Illuminate\Support\Collection
+     */
     public function items()
     {
         return collect($this->items)->sortBy('name');
     }
 
+    /**
+     * Add new item to invoice item collection.
+     *
+     * @param \App\Services\InvoiceDrafts\Item $item
+     *
+     * @return \App\Services\InvoiceDrafts\Item
+     */
     public function addItem(Item $item)
     {
         $this->items[] = $item;
@@ -30,26 +70,56 @@ class InvoiceDraft
         return $item;
     }
 
+    /**
+     * Remove item from the collection.
+     *
+     * @param int $itemKey Key of invoice item.
+     *
+     * @return void
+     */
     public function removeItem($itemKey)
     {
         unset($this->items[$itemKey]);
     }
 
+    /**
+     * Empty out invoice draft items.
+     *
+     * @return void
+     */
     public function empty()
     {
         $this->items = [];
     }
 
+    /**
+     * Get invoice total amount.
+     *
+     * @return int Total amount of invoice.
+     */
     public function getTotal()
     {
         return $this->items()->sum('amount');
     }
 
+    /**
+     * Get invoice items count.
+     *
+     * @return int Items count of invoice.
+     */
     public function getItemsCount()
     {
         return $this->items()->count();
     }
 
+    /**
+     * Update an invoice item.
+     *
+     * @param int $itemKey       The item key
+     * @param array $newItemData The item attributes.
+     *
+     * @return null|\App\Services\InvoiceDrafts\Item
+     */
     public function updateItem($itemKey, $newItemData)
     {
         if (!isset($this->items[$itemKey])) {
@@ -63,6 +133,11 @@ class InvoiceDraft
         return $item;
     }
 
+    /**
+     * Store invoice draft to database as invoice record.
+     *
+     * @return \App\Entities\Invoices\Invoice The saved invoice.
+     */
     public function store()
     {
         $invoice = new Invoice();
@@ -81,6 +156,11 @@ class InvoiceDraft
         return $invoice;
     }
 
+    /**
+     * Get invoice items in array format.
+     *
+     * @return array Array of items.
+     */
     protected function getItemsArray()
     {
         $items = [];
@@ -94,6 +174,11 @@ class InvoiceDraft
         return $items;
     }
 
+    /**
+     * Destroy current invocie draft from the session.
+     *
+     * @return void
+     */
     public function destroy()
     {
         $cart = app(InvoiceDraftCollection::class);
diff --git a/app/Services/InvoiceDraft/InvoiceDraftCollection.php b/app/Services/InvoiceDraft/InvoiceDraftCollection.php
index dac625d..9c619d3 100644
--- a/app/Services/InvoiceDraft/InvoiceDraftCollection.php
+++ b/app/Services/InvoiceDraft/InvoiceDraftCollection.php
@@ -11,15 +11,36 @@ use Illuminate\Support\Collection;
  */
 class InvoiceDraftCollection
 {
+    /**
+     * Instance of invoice draft.
+     *
+     * @var string
+     */
     private $instance;
+
+    /**
+     * Laravel session.
+     *
+     * @var \Illuminate\Session\SessionManager
+     */
     private $session;
 
+    /**
+     * Create new invoice draft instance.
+     */
     public function __construct()
     {
         $this->session = session();
         $this->instance('drafts');
     }
 
+    /**
+     * Set new instance name of invoice draft.
+     *
+     * @param string $instance Invoice draft instance name.
+     *
+     * @return \App\Services\InvoiceDrafts\InvoiceDraft
+     */
     public function instance($instance = null)
     {
         $instance = $instance ?: 'drafts';
@@ -29,11 +50,21 @@ class InvoiceDraftCollection
         return $this;
     }
 
+    /**
+     * Get instance name of current invoice draft.
+     *
+     * @return string
+     */
     public function currentInstance()
     {
         return str_replace('invoices.', '', $this->instance);
     }
 
+    /**
+     * Add new invoice draft.
+     *
+     * @param \App\Services\InvoiceDrafts\InvoiceDraft $draft Invoice draft.
+     */
     public function add(InvoiceDraft $draft)
     {
         $content = $this->getContent();
@@ -45,6 +76,13 @@ class InvoiceDraftCollection
         return $draft;
     }
 
+    /**
+     * Get an invoice draft.
+     *
+     * @param string $draftKey The invoice draft key.
+     *
+     * @return null|\App\Services\InvoiceDrafts\InvoiceDraft
+     */
     public function get($draftKey)
     {
         $content = $this->getContent();
@@ -53,6 +91,14 @@ class InvoiceDraftCollection
         }
     }
 
+    /**
+     * Update invoice draft attribute.
+     *
+     * @param string $draftKey        Invoice draft key.
+     * @param array  $draftAttributes Invoice draft attribute to be updated.
+     *
+     * @return \App\Services\InvoiceDrafts\InvoiceDraft
+     */
     public function updateDraftAttributes($draftKey, $draftAttributes)
     {
         $content = $this->getContent();
@@ -67,6 +113,13 @@ class InvoiceDraftCollection
         return $content[$draftKey];
     }
 
+    /**
+     * Empty out an invoice draft items.
+     *
+     * @param string $draftKey Invoice draft key.
+     *
+     * @return void
+     */
     public function emptyDraft($draftKey)
     {
         $content = $this->getContent();
@@ -74,6 +127,13 @@ class InvoiceDraftCollection
         $this->session->put($this->instance, $content);
     }
 
+    /**
+     * Remove an invocie draft.
+     *
+     * @param string $draftKey Invoice draft key.
+     *
+     * @return void
+     */
     public function removeDraft($draftKey)
     {
         $content = $this->getContent();
@@ -81,11 +141,21 @@ class InvoiceDraftCollection
         $this->session->put($this->instance, $content);
     }
 
+    /**
+     * Get invoice draft collection content.
+     *
+     * @return \Illuminate\Support\Collection
+     */
     public function content()
     {
         return $this->getContent();
     }
 
+    /**
+     * Get invoice draft collection content.
+     *
+     * @return \Illuminate\Support\Collection
+     */
     protected function getContent()
     {
         $content = $this->session->has($this->instance) ? $this->session->get($this->instance) : collect([]);
@@ -93,16 +163,34 @@ class InvoiceDraftCollection
         return $content;
     }
 
+    /**
+     * Get invoice draft keys collection.
+     *
+     * @return \Illuminate\Support\Collection Collection of keys.
+     */
     public function keys()
     {
         return $this->getContent()->keys();
     }
 
+    /**
+     * Destroy an invoice draft.
+     *
+     * @return void
+     */
     public function destroy()
     {
         $this->session->remove($this->instance);
     }
 
+    /**
+     * Add an item to an invoice draft.
+     *
+     * @param string                           $draftKey Invoice draft key.
+     * @param \App\Services\InvoiceDrafts\Item $item     Invoice item.
+     *
+     * @return \App\Services\InvoiceDrafts\Item.
+     */
     public function addItemToDraft($draftKey, Item $item)
     {
         $content = $this->getContent();
@@ -113,6 +201,15 @@ class InvoiceDraftCollection
         return $item;
     }
 
+    /**
+     * Update invoice draft item attributes.
+     *
+     * @param string $draftKey   Invoice draft key.
+     * @param string $itemKey    Invoice item key.
+     * @param array $newItemData Array of item attribute.
+     *
+     * @return void
+     */
     public function updateDraftItem($draftKey, $itemKey, $newItemData)
     {
         $content = $this->getContent();
@@ -121,6 +218,14 @@ class InvoiceDraftCollection
         $this->session->put($this->instance, $content);
     }
 
+    /**
+     * Remove an invoice draft item.
+     *
+     * @param string $draftKey Invoice draft key.
+     * @param string $itemKey  Invoice item key.
+     *
+     * @return void
+     */
     public function removeItemFromDraft($draftKey, $itemKey)
     {
         $content = $this->getContent();
@@ -129,16 +234,31 @@ class InvoiceDraftCollection
         $this->session->put($this->instance, $content);
     }
 
+    /**
+     * Get invoice drafts count.
+     *
+     * @return int
+     */
     public function count()
     {
         return $this->getContent()->count();
     }
 
+    /**
+     * Check if current invoice draft is empty.
+     *
+     * @return boolean
+     */
     public function isEmpty()
     {
         return $this->count() == 0;
     }
 
+    /**
+     * Check if current invoice draft has content.
+     *
+     * @return boolean
+     */
     public function hasContent()
     {
         return !$this->isEmpty();
diff --git a/app/Services/InvoiceDraft/Item.php b/app/Services/InvoiceDraft/Item.php
index a0c4fec..93c01d1 100644
--- a/app/Services/InvoiceDraft/Item.php
+++ b/app/Services/InvoiceDraft/Item.php
@@ -9,15 +9,38 @@ namespace App\Services\InvoiceDrafts;
  */
 class Item
 {
+    /**
+     * Invoice item description.
+     *
+     * @var string
+     */
     public $description;
+
+    /**
+     * Invoice item amount.
+     *
+     * @var int
+     */
     public $amount;
 
+    /**
+     * Create new invoice item.
+     *
+     * @param array $itemDetail Detail of an invoice item.
+     */
     public function __construct(array $itemDetail)
     {
         $this->description = $itemDetail['description'];
         $this->amount = $itemDetail['amount'];
     }
 
+    /**
+     * Update attribute of an invoice item.
+     *
+     * @param array $newItemData Item attribute that will be replaced.
+     *
+     * @return \App\Services\InvoiceDrafts\Item
+     */
     public function updateAttribute(array $newItemData)
     {
         if (isset($newItemData['description'])) {