Index: kernel/db/db_event_handler.php
===================================================================
--- kernel/db/db_event_handler.php	(revision 14318)
+++ kernel/db/db_event_handler.php	(working copy)
@@ -2931,4 +2931,15 @@
 			$clones[$subitem_prefix] = Array ('ParentPrefix' => $event->Prefix);
 			$this->Application->setUnitOption($event->MasterEvent->Prefix, 'Clones', $clones);
 		}
+
+		/**
+		 * Returns constrain for priority calculations
+		 *
+		 * @see PriorityEventHandler
+		 * @param kEvent $event
+		 */
+		function OnGetConstrainInfo(&$event)
+		{
+			$event->setEventParam('constrain_info', Array ('', ''));
+		}
 	}
\ No newline at end of file
Index: units/categories/categories_event_handler.php
===================================================================
--- units/categories/categories_event_handler.php	(revision 14318)
+++ units/categories/categories_event_handler.php	(working copy)
@@ -763,12 +763,6 @@
 				$object->SetDBField('Template', $this->_getDefaultDesign());
 			}
 
-			$priority_helper =& $this->Application->recallObject('PriorityHelper');
-			/* @var $priority_helper kPriorityHelper */
-
-			// 3. prepare priorities dropdown
-			$priority_helper->preparePriorities($event, true, 'ParentId = ' . $category_id);
-
 			// 4. set default owner
 			$object->SetDBField('CreatedById', $this->Application->RecallVar('user_id'));
 		}
@@ -801,16 +795,6 @@
 				return ;
 			}
 
-			// 1. update priorities
-			$tmp = $this->Application->RecallVar('priority_changes'.$this->Application->GetVar('m_wid'));
-			$changes = $tmp ? unserialize($tmp) : Array ();
-			$changed_ids = array_keys($changes);
-
-			$priority_helper =& $this->Application->recallObject('PriorityHelper');
-			/* @var $priority_helper kPriorityHelper */
-
-			$priority_helper->updatePriorities($event, $changes, Array (0 => $event->getEventParam('ids')));
-
 			if ($this->Application->RecallVar('PermCache_UpdateRequired')) {
 				$this->Application->RemoveVar('IsRootCategory_' . $this->Application->GetVar('m_wid'));
 			}
@@ -819,7 +803,7 @@
 			$this->_resetMenuCache();
 
 			if ($is_editing) {
-				// 2. send email event to category owner, when it's status is changed (from admin)
+				// send email event to category owner, when it's status is changed (from admin)
 				$object->SwitchToLive();
 				$new_statuses = $this->_getCategoryStatus($ids);
 				$process_statuses = Array (STATUS_ACTIVE, STATUS_DISABLED);
@@ -867,12 +851,6 @@
 				return ;
 			}
 
-			$priority_helper =& $this->Application->recallObject('PriorityHelper');
-			/* @var $priority_helper kPriorityHelper */
-
-			$category_id = $this->Application->GetVar('m_cat_id');
-			$priority_helper->preparePriorities($event, true, 'ParentId = ' . $category_id);
-
 			parent::OnPreSaveCreated($event);
 		}
 
@@ -895,7 +873,6 @@
 			$this->Conn->Query($sql);
 		}
 
-
 		/**
 		* Exclude root categories from deleting
 		*
@@ -920,25 +897,6 @@
 					$this->Application->StoreVar('root_delete_error', 1);
 				}
 			}
-
-			$change_events = Array ('OnPreSave', 'OnPreSaveCreated', 'OnUpdate', 'OnSave');
-			if ($type == 'after' && in_array($event->Name, $change_events)) {
-				$object =& $event->getObject();
-
-				$tmp = $this->Application->RecallVar('priority_changes'.$this->Application->GetVar('m_wid'));
-				$changes = $tmp ? unserialize($tmp) : array();
-
-				if (!isset($changes[$object->GetID()])) {
-					$changes[$object->GetId()]['old'] = $object->GetID() == 0 ? 'new' : $object->GetDBField('OldPriority');
-				}
-
-				if ($changes[$object->GetId()]['old'] == $object->GetDBField('Priority')) return ;
-
-				$changes[$object->GetId()]['new'] = $object->GetDBField('Priority');
-				$changes[$object->GetId()]['parent'] = $object->GetDBField('ParentId');
-
-				$this->Application->StoreVar('priority_changes'.$this->Application->GetVar('m_wid'), serialize($changes));
-			}
 		}
 
 		/**
@@ -1026,14 +984,6 @@
 			}
 			$this->clearSelectedIDs($event);
 
-			// update priorities
-			$priority_helper =& $this->Application->recallObject('PriorityHelper');
-			/* @var $priority_helper kPriorityHelper */
-
-			// after deleting categories, all priorities should be recalculated
-			$parent_id = $this->Application->GetVar('m_cat_id');
-			$priority_helper->recalculatePriorities($event, 'ParentId = ' . $parent_id);
-
 			$this->Application->StoreVar('RefreshStructureTree', 1);
 			$this->_resetMenuCache();
 		}
@@ -1159,13 +1109,21 @@
 			/* @var $priority_helper kPriorityHelper */
 
 			if ($clipboard_data['cut']) {
-				$priority_helper->recalculatePriorities($event, 'ParentId = '.$source_category_id);
+				$ids = $priority_helper->recalculatePriorities($event, 'ParentId = '.$source_category_id);
+
+				if ($ids) {
+					$priority_helper->massUpdateChanged($event->Prefix, $ids);
+				}
 			}
 
 			// recalculate priorities of newly pasted categories in destination category
 			$parent_id = $this->Application->GetVar('m_cat_id');
-			$priority_helper->recalculatePriorities($event, 'ParentId = ' . $parent_id);
+			$ids = $priority_helper->recalculatePriorities($event, 'ParentId = ' . $parent_id);
 
+			if ($ids) {
+				$priority_helper->massUpdateChanged($event->Prefix, $ids);
+			}
+
 			if ($clipboard_data['cut'] || $clipboard_data['copy']) {
 				// rebuild with progress bar
 				if ($this->Application->ConfigValue('QuickCategoryPermissionRebuild')) {
@@ -1966,37 +1924,9 @@
 				unset($field_options['options'][$remove_category]);
 			}
 			$object->SetFieldOptions('ParentId', $field_options);
-
-			$priority_helper =& $this->Application->recallObject('PriorityHelper');
-			/* @var $priority_helper kPriorityHelper */
-
-			$priority_helper->preparePriorities($event, false, 'ParentId = '.$object->GetDBField('ParentId'));
-
-			// storing prioriry right after load for comparing when updating
-			$object->SetDBField('OldPriority', $object->GetDBField('Priority'));
 		}
 
 		/**
-		 * Builds list
-		 *
-		 * @param kEvent $event
-		 * @access protected
-		 */
-		function OnListBuild(&$event)
-		{
-			parent::OnListBuild($event);
-
-			if (!$this->Application->isAdminUser) {
-				return ;
-			}
-
-			$priority_helper =& $this->Application->recallObject('PriorityHelper');
-			/* @var $priority_helper kPriorityHelper */
-
-			$priority_helper->preparePriorities($event, false, 'ParentId = '.$this->Application->GetVar('m_cat_id'));
-		}
-
-		/**
 		 * Enter description here...
 		 *
 		 * @param kEvent $event
@@ -2059,39 +1989,9 @@
 				return;
 			}
 
-			$object =& $event->getObject( Array('skip_autoload' => true) );
-			$ids = $this->StoreSelectedIDs($event);
+			$this->Application->SetVar('priority_prefix', $event->getPrefixSpecial());
+			$event->CallSubEvent('priority:' . $event->Name);
 
-			if ($ids) {
-				$id_field = $this->Application->getUnitOption($event->Prefix, 'IDField');
-				$table_name = $this->Application->getUnitOption($event->Prefix, 'TableName');
-				$parent_id = $this->Application->GetVar('m_cat_id');
-
-				$sql = 'SELECT Priority, '.$id_field.'
-						FROM '.$table_name.'
-						WHERE '.$id_field.' IN ('.implode(',', $ids).')';
-				$priorities = $this->Conn->GetCol($sql, $id_field);
-
-				$priority_helper =& $this->Application->recallObject('PriorityHelper');
-				/* @var $priority_helper kPriorityHelper */
-
-				foreach ($ids as $id) {
-					$new_priority = $priorities[$id] + ($event->Name == 'OnMassMoveUp' ? +1 : -1);
-
-					$changes = Array (
-						$id	=>	Array ('old' => $priorities[$id], 'new' => $new_priority, 'parent' => $parent_id),
-					);
-
-					$sql = 'UPDATE '.$table_name.'
-							SET Priority = '.$new_priority.'
-							WHERE '.$id_field.' = '.$id;
-					$this->Conn->Query($sql);
-
-					$priority_helper->updatePriorities($event, $changes, Array ($id => $id));
-				}
-			}
-
-			$this->clearSelectedIDs($event);
 			$this->Application->StoreVar('RefreshStructureTree', 1);
 			$this->_resetMenuCache();
 		}
@@ -2108,11 +2008,9 @@
 				return;
 			}
 
-			$priority_helper =& $this->Application->recallObject('PriorityHelper');
-			/* @var $priority_helper kPriorityHelper */
+			$this->Application->SetVar('priority_prefix', $event->getPrefixSpecial());
+			$event->CallSubEvent('priority:OnRecalculatePriorities');
 
-			$parent_id = $this->Application->GetVar('m_cat_id');
-			$priority_helper->recalculatePriorities($event, 'ParentId = ' . $parent_id);
 			$this->_resetMenuCache();
 		}
 
@@ -2438,4 +2336,34 @@
 				$object->setID($id);
 			}
 		}
+
+		/**
+		 * Returns constrain for priority calculations
+		 *
+		 * @see PriorityEventHandler
+		 * @param kEvent $event
+		 */
+		function OnGetConstrainInfo(&$event)
+		{
+			$contarain = ''; // for OnSave
+
+			$event_name = $event->getEventParam('original_event');
+			$actual_event_name = $event->getEventParam('actual_event');
+
+			if ( $actual_event_name == 'OnSavePriorityChanges' || $event_name == 'OnAfterItemLoad' || $event_name == 'OnAfterItemDelete' ) {
+				$object =& $event->getObject();
+				$contarain = 'ParentId = ' . $object->GetDBField('ParentId');
+			}
+			elseif ( $actual_event_name == 'OnPreparePriorities' ) {
+				$contarain = 'ParentId = ' . $this->Application->GetVar('m_cat_id');
+			}
+			elseif ($event_name == 'OnSave') {
+				$contarain = '';
+			}
+			else {
+				$contarain = 'ParentId = ' . $this->Application->GetVar('m_cat_id');
+			}
+
+			$event->setEventParam('constrain_info', Array ($contarain, ''));
+		}
 	}
\ No newline at end of file
Index: units/helpers/priority_helper.php
===================================================================
--- units/helpers/priority_helper.php	(revision 14318)
+++ units/helpers/priority_helper.php	(working copy)
@@ -16,16 +16,16 @@
 
 	class kPriorityHelper extends kHelper {
 
-
 		/**
 		 * Prepares options for priority dropdown
 		 *
 		 * @param kEvent $event
 		 * @param bool $is_new for newly created items add new priority to the end
 		 * @param string $constrain constrain for priority selection (if any)
+		 * @param string $joins left joins, used by constrain (if any)
 		 *
 		 */
-		function preparePriorities(&$event, $is_new = false, $constrain = '')
+		function preparePriorities(&$event, $is_new = false, $constrain = '', $joins = '')
 		{
 			$object =& $event->getObject();
 
@@ -33,30 +33,33 @@
 			$table_name = $this->Application->getUnitOption($event->Prefix, 'TableName');
 
 			$sql = 'SELECT COUNT(*)
-					FROM '.$table_name;
-			if ($constrain) {
-				$sql .= ' WHERE '.$constrain;
+					FROM '.$table_name . ' item_table
+					' . $joins;
+
+			if ( $constrain ) {
+				$sql .= ' WHERE ' . $this->normalizeConstrain($constrain);
 			}
 
-			if (!isset($object->Fields['OldPriority'])) {
+			if ( !isset($object->Fields['OldPriority']) ) {
 				$object->VirtualFields['OldPriority'] = Array('type' => 'int', 'default' => 0);
 			}
 
 			$items_count = $this->Conn->GetOne($sql);
 
-			// instanceof is not used, because PHP4 doesn't support it
+			// TODO: instanceof is not used, because PHP4 doesn't support it
 			$current_priority = is_a($object, 'kDBList') ? 0 : $object->GetDBField('Priority');
 
-			if ($is_new || $current_priority == -($items_count+1)) {
+			if ( $is_new || $current_priority == -($items_count + 1) ) {
 				$items_count++;
 			}
 
-			if ($is_new) {
+			if ( $is_new ) {
 				// add new item to the end of list
 				$object->SetDBField('Priority', -$items_count);
 				$object->SetDBField('OldPriority', -$items_count);
 			}
 			else {
+				// storing prioriry right after load for comparing when updating
 				$object->SetDBField('OldPriority', $current_priority);
 			}
 
@@ -65,26 +68,29 @@
 			}
 
 			$object->SetFieldOptions('Priority', $field_options);
-			// storing prioriry right after load for comparing when updating
 		}
 
 		/**
 		 * Updates priorities for changed items
 		 *
 		 * @param kEvent $event
-		 * @param Array $changes = Array (ID => Array ('parent' => ..., 'new' => ..., 'old' => ...), ...)
+		 * @param Array $changes = Array (ID => Array ('constrain' => ..., 'new' => ..., 'old' => ...), ...)
 		 * @param Array $new_ids = Array (temp_id => live_id)
 		 * @param string $constrain
+		 * @param string $joins
 		 */
-		function updatePriorities(&$event, $changes, $new_ids, $constrain = '')
+		function updatePriorities(&$event, $changes, $new_ids, $constrain = '', $joins = '')
 		{
-			if (!$changes) {
+			// TODO: no need pass external $constrain, since the one from $pair is used
+
+			if ( !$changes ) {
 				// no changes to process
 				return Array ();
 			}
+
 			list ($id, $pair) = each($changes);
 
-			if (!$id && !array_key_exists('parent', $pair)) {
+			if ( !$id && !isset($pair['constrain']) ) {
 				// adding new item without constrain -> priority stays the same
 				return Array ($id);
 			}
@@ -92,57 +98,69 @@
 			$id_field = $this->Application->getUnitOption($event->Prefix, 'IDField');
 			$table_name = $this->Application->getUnitOption($event->Prefix, 'TableName');
 
-			$ids = array();
+			$ids = Array ();
 			$not_processed = array_keys($changes);
 
 			foreach ($changes as $id => $pair) {
 				array_push($ids, $id);
-				$constrain = isset($pair['parent']) ? 'ParentId = '.$pair['parent'].' AND ' : '';
 
-				if ($pair['old'] == 'new') {
+				$constrain = isset($pair['constrain']) ? $this->normalizeConstrain($pair['constrain']) . ' AND ' : '';
+
+				if ( $pair['old'] == 'new' ) {
 					// replace 0 with newly created item id (from $new_ids mapping)
 					$not_processed[ array_search($id, $not_processed) ] = $new_ids[$id];
 					$id = $new_ids[$id];
 
-					$sql = 'SELECT MIN(Priority)
-							FROM '.$table_name.'
-							WHERE '.$constrain.' '.$id_field.' NOT IN ('.implode(',', $not_processed).')';
+					$sql = 'SELECT MIN(item_table.Priority)
+							FROM ' . $table_name . ' item_table
+							' . $joins . '
+							WHERE ' . $constrain . ' ' . $id_field . ' NOT IN (' . implode(',', $not_processed) . ')';
 					$min_priority = (int)$this->Conn->GetOne($sql) - 1;
 
 					if ($pair['new'] < $min_priority) {
 						$pair['new'] = $min_priority;
 					}
+
 					$pair['old'] = $min_priority;
 				}
 
-				if ($pair['new'] < $pair['old']) {
-					$set = '	SET Priority = Priority + 1';
-					$where =' WHERE '.$constrain.'
-								Priority >= '.$pair['new'].'
+				if ( $pair['new'] < $pair['old'] ) {
+					$set = 'SET item_table.Priority = item_table.Priority + 1';
+					$where =' WHERE ' . $constrain . '
+								item_table.Priority >= ' . $pair['new'] . '
 								AND
-								Priority < '.$pair['old'].'
+								item_table.Priority < ' . $pair['old'] . '
 								AND
-								'.$id_field.' NOT IN ('.implode(',', $not_processed).')';
+								' . $id_field . ' NOT IN (' . implode(',', $not_processed) . ')';
 				}
-				elseif ($pair['new'] > $pair['old']) {
-					$set = '	SET Priority = Priority - 1';
-					$where ='	WHERE '.$constrain.'
-								Priority > '.$pair['old'].'
+				elseif ( $pair['new'] > $pair['old'] ) {
+					$set = 'SET item_table.Priority = item_table.Priority - 1';
+					$where ='	WHERE ' . $constrain . '
+								item_table.Priority > ' . $pair['old'] . '
 								AND
-								Priority <= '.$pair['new'].'
+								item_table.Priority <= ' . $pair['new'] . '
 								AND
-								'.$id_field.' NOT IN ('.implode(',', $not_processed).')';
+								' . $id_field . ' NOT IN (' . implode(',', $not_processed) . ')';
 				}
 				else {
-					$set = 'SET Priority = '.$pair['new'];
-					$where = ' WHERE '.$id_field.' = '.$id;
+					$set = 'SET item_table.Priority = ' . $pair['new'];
+					$where = ' WHERE ' . $id_field . ' = ' . $id;
 				}
-				$ids = array_merge($ids, $this->Conn->GetCol('SELECT '.$id_field.' FROM '.$table_name.$where));
-				$q = 'UPDATE '.$table_name.' '.$set.$where;
+
+				$sql = 'SELECT item_table.' . $id_field . '
+						FROM ' . $table_name . ' item_table
+						' . $joins . '
+						' . $where;
+				$ids = array_merge($ids, $this->Conn->GetCol($sql));
+
+				$q = 'UPDATE ' . $table_name . ' item_table
+						' . $joins . '
+						' . $set . $where;
 				$this->Conn->Query($q);
 
 				unset( $not_processed[array_search($id, $not_processed)] );
 			}
+
 			return $ids;
 		}
 
@@ -151,25 +169,67 @@
 		 *
 		 * @param kEvent $event
 		 * @param string $constrain
+		 * @param string $joins
 		 */
-		function recalculatePriorities(&$event, $constrain = '')
+		function recalculatePriorities(&$event, $constrain = '', $joins = '')
 		{
 			$id_field = $this->Application->getUnitOption($event->Prefix, 'IDField');
 			$table_name = $this->Application->getUnitOption($event->Prefix, 'TableName');
+			$constrain = $this->normalizeConstrain($constrain);
 
-			$sql = 'SELECT '.$id_field.'
-					FROM '.$table_name.
-					($constrain ? ' WHERE '.$constrain : '').'
-					ORDER BY Priority DESC';
+			$sql = 'SELECT ' . $id_field . '
+					FROM ' . $table_name . ' item_table ' .
+					$joins . ' ' .
+					($constrain ? ' WHERE ' . $constrain : '') . '
+					ORDER BY item_table.Priority DESC';
 
 			$items = $this->Conn->GetCol($sql);
 
 			foreach ($items as $item_number => $item_id) {
-				$sql = 'UPDATE '.$table_name.'
-						SET Priority = '.-($item_number + 1).'
-						WHERE '.$id_field.' = '.$item_id;
+				$sql = 'UPDATE ' . $table_name . '
+						SET Priority = ' . -($item_number + 1) . '
+						WHERE ' . $id_field . ' = ' . $item_id;
 				$this->Conn->Query($sql);
 			}
+
 			return $items;
 		}
+
+		/**
+		 * Adds current table name into constrain if doesn't have it already (to prevent ambiguous columns during joins)
+		 *
+		 * @param string $constrain
+		 * @return string
+		 */
+		function normalizeConstrain($constrain)
+		{
+			if ( strpos($constrain, '.') === false ) {
+				return 'item_table.' . $constrain;
+			}
+
+			return $constrain;
+		}
+
+		/**
+		 * Peforms fake kDBItem::Update call, so any OnBefore/OnAfter events would be notified of priority change
+		 *
+		 * @param string $prefix
+		 * @param Array $ids
+		 */
+		function massUpdateChanged($prefix, $ids)
+		{
+			$ids = array_unique($ids);
+
+			$dummy =& $this->Application->recallObject($prefix . '.-dummy', null, Array ('skip_autoload' => true));
+			/* @var $dummy kDBItem */
+
+			$sql = 	$dummy->GetSelectSQL() . '
+					WHERE ' . $dummy->TableName . '.' . $dummy->IDField . ' IN (' . implode(',', $ids) . ')';
+			$records = $this->Conn->Query($sql);
+
+			foreach ($records as $record) {
+				$dummy->LoadFromHash($record);
+				$dummy->Update();
+			}
+		}
 	}
\ No newline at end of file
Index: units/priorites/priorites_config.php
===================================================================
--- units/priorites/priorites_config.php	(revision 0)
+++ units/priorites/priorites_config.php	(revision 0)
@@ -0,0 +1,31 @@
+<?php
+
+	$config	= Array (
+		'Prefix' => 'priority',
+		'EventHandlerClass' => Array ('class' => 'PriorityEventHandler', 'file' => 'priority_eh.php', 'build_event' => 'OnBuild'),
+
+		'QueryString' => Array (
+			1 => 'prefix',
+			2 => 'event',
+		),
+
+		'Hooks' => Array (
+			Array (
+				'Mode' => hAFTER,
+				'Conditional' => false,
+				'HookToPrefix' => 'adm',
+				'HookToSpecial' => '*',
+				'HookToEvent' => Array ('OnBeforeShutdown'),
+				'DoPrefix' => 'priority',
+				'DoSpecial' => '*',
+				'DoEvent' => 'OnBeforeShutdown',
+				'Conditional' => false,
+			),
+		),
+
+		'PermSection' => Array ('main' => 'custom'),
+
+		'ProcessPrefixes' => Array(
+			'c', 'st'
+		),
+	);
Index: units/priorites/priority_eh.php
===================================================================
--- units/priorites/priority_eh.php	(revision 0)
+++ units/priorites/priority_eh.php	(revision 0)
@@ -0,0 +1,369 @@
+<?php
+
+class PriorityEventHandler extends kDBEventHandler {
+
+	/**
+	 * Allows to override standart permission mapping
+	 *
+	 */
+	function mapPermissions()
+	{
+		parent::mapPermissions();
+
+		$permissions = Array (
+			'OnRecalculatePriorities' => Array ('self' => true),
+		);
+
+		$this->permMapping = array_merge($this->permMapping, $permissions);
+	}
+
+	function mapEvents()
+	{
+		parent::mapEvents();
+
+		$events_map = Array (
+			'OnMassMoveUp' => 'OnChangePriority',
+			'OnMassMoveDown' => 'OnChangePriority',
+		);
+
+		$this->eventMethods = array_merge($this->eventMethods, $events_map);
+	}
+
+	/**
+	 * Enter description here...
+	 *
+	 * @param kEvent $event
+	 */
+	function OnAfterConfigRead(&$event)
+	{
+		$hooks = Array(
+			Array(
+				'Mode' => hAFTER,
+				'Conditional' => false,
+				'HookToPrefix' => '',
+				'HookToSpecial' => '*',
+				'HookToEvent' => Array('OnAfterItemLoad', 'OnPreCreate', 'OnListBuild'),
+				'DoPrefix' => 'priority',
+				'DoSpecial' => '*',
+				'DoEvent' => 'OnPreparePriorities',
+				'Conditional' => false,
+			),
+			Array(
+				'Mode' => hBEFORE,
+				'Conditional' => false,
+				'HookToPrefix' => '',
+				'HookToSpecial' => '*',
+				'HookToEvent' => Array('OnPreSaveCreated'),
+				'DoPrefix' => 'priority',
+				'DoSpecial' => '*',
+				'DoEvent' => 'OnPreparePriorities',
+				'Conditional' => false,
+			),
+			Array(
+				'Mode' => hAFTER,
+				'Conditional' => false,
+				'HookToPrefix' => '',
+				'HookToSpecial' => '*',
+				'HookToEvent' => Array('OnPreSave', 'OnPreSaveCreated', 'OnSave', 'OnUpdate'),
+				'DoPrefix' => 'priority',
+				'DoSpecial' => '*',
+				'DoEvent' => 'OnSavePriorityChanges',
+				'Conditional' => false,
+			),
+			Array(
+				'Mode' => hAFTER,
+				'Conditional' => false,
+				'HookToPrefix' => '',
+				'HookToSpecial' => '*',
+				'HookToEvent' => Array('OnSave'),
+				'DoPrefix' => 'priority',
+				'DoSpecial' => '*',
+				'DoEvent' => 'OnSaveItems',
+				'Conditional' => false,
+			),
+			Array(
+				'Mode' => hBEFORE,
+				'Conditional' => false,
+				'HookToPrefix' => '',
+				'HookToSpecial' => '*',
+				'HookToEvent' => Array('OnBeforeItemCreate'),
+				'DoPrefix' => 'priority',
+				'DoSpecial' => '*',
+				'DoEvent' => 'OnItemCreate',
+				'Conditional' => false,
+			),
+			Array(
+				'Mode' => hBEFORE,
+				'Conditional' => false,
+				'HookToPrefix' => '',
+				'HookToSpecial' => '*',
+				'HookToEvent' => Array('OnAfterItemDelete'),
+				'DoPrefix' => 'priority',
+				'DoSpecial' => '*',
+				'DoEvent' => 'OnItemDelete',
+				'Conditional' => false,
+			)
+		);
+
+		$prefixes = $this->Application->getUnitOption($event->Prefix, 'ProcessPrefixes');
+
+		foreach ($prefixes as $prefix) {
+			foreach ($hooks as $hook) {
+				if ( !is_array($hook['HookToEvent']) ) {
+					$hook['HookToEvent'] = Array($hook['HookToEvent']);
+				}
+
+				foreach ($hook['HookToEvent'] as $hook_event) {
+					$this->Application->registerHook(
+						$prefix,
+						$hook['HookToSpecial'],
+						$hook_event,
+						$hook['Mode'],
+						$event->Prefix,
+						$hook['DoSpecial'],
+						$hook['DoEvent'],
+						$hook['Conditional']
+					);
+				}
+			}
+		}
+	}
+
+	/**
+	 * Should be hooked to OnAfterItemLoad, OnPreSaveCreated (why latter?)
+	 *
+	 * @param kEvent $event
+	 */
+	function OnPreparePriorities(&$event)
+	{
+		if ( !$this->Application->isAdminUser ) {
+			return ;
+		}
+
+		$priority_helper =& $this->Application->recallObject('PriorityHelper');
+		/* @var $priority_helper kPriorityHelper */
+
+		list ($constrain, $joins) = $this->getConstrainInfo($event);
+		$is_new = $event->MasterEvent->Name == 'OnPreCreate' || $event->MasterEvent->Name == 'OnPreSaveCreated';
+		$priority_helper->preparePriorities($event->MasterEvent, $is_new, $constrain, $joins);
+	}
+
+	/**
+	 * Enter description here...
+	 *
+	 * @param kEvent $event
+	 */
+	function OnSavePriorityChanges(&$event)
+	{
+		if ($event->MasterEvent->status != erSUCCESS) {
+			// don't update priorities, when OnSave validation failed
+			return ;
+		}
+
+		$object =& $event->MasterEvent->getObject();
+
+		$tmp = $this->Application->RecallVar('priority_changes'.$this->Application->GetVar('m_wid'));
+		$changes = $tmp ? unserialize($tmp) : array();
+
+		if (!isset($changes[$object->GetID()])) {
+			$changes[$object->GetId()]['old'] = $object->GetID() == 0 ? 'new' : $object->GetDBField('OldPriority');
+		}
+
+		if ($changes[$object->GetId()]['old'] == $object->GetDBField('Priority')) return ;
+		$changes[$object->GetId()]['new'] = $object->GetDBField('Priority');
+
+		list ($constrain, $joins) = $this->getConstrainInfo($event);
+
+		if ($constrain) {
+			$changes[$object->GetId()]['constrain'] = $constrain;
+		}
+
+		$this->Application->StoreVar('priority_changes'.$this->Application->GetVar('m_wid'), serialize($changes));
+	}
+
+	/**
+	 * Enter description here...
+	 *
+	 * @param kEvent $event
+	 */
+	function OnItemDelete(&$event)
+	{
+		// just store the prefix in which the items were deleted
+		$del = $this->Application->RecallVar('priority_deleted' . $this->Application->GetVar('m_wid'));
+		$del = $del ? unserialize($del) : array();
+
+		list ($constrain, $joins) = $this->getConstrainInfo($event);
+		$cache_key = crc32($event->MasterEvent->Prefix . ':' . $constrain . ':' . $joins);
+
+		if ( !isset($del[$cache_key]) ) {
+			$del[$cache_key] = Array (
+				'prefix' => $event->MasterEvent->Prefix,
+				'constrain' => $constrain,
+				'joins' => $joins,
+			);
+
+			$this->Application->StoreVar('priority_deleted' . $this->Application->GetVar('m_wid'), serialize($del));
+		}
+	}
+
+	/**
+	 * Called before script shut-down and recalculate all deleted prefixes, to avoid recalculation on each deleted item
+	 *
+	 * @param kEvent $event
+	 */
+	function OnBeforeShutDown(&$event)
+	{
+		$del = $this->Application->RecallVar('priority_deleted'.$this->Application->GetVar('m_wid'));
+		$del = $del ? unserialize($del) : array();
+
+		$priority_helper =& $this->Application->recallObject('PriorityHelper');
+		/* @var $priority_helper kPriorityHelper */
+
+		foreach ($del as $del_info) {
+			$dummy_event = new kEvent( array('prefix'=>$del_info['prefix'], 'name'=>'Dummy' ) );
+			$ids = $priority_helper->recalculatePriorities($dummy_event, $del_info['constrain'], $del_info['joins']);
+
+			if ($ids) {
+				$priority_helper->massUpdateChanged($del_info['prefix'], $ids);
+			}
+		}
+
+		$this->Application->RemoveVar('priority_deleted'.$this->Application->GetVar('m_wid'));
+	}
+
+	/**
+	 * Enter description here...
+	 *
+	 * @param kEvent $event
+	 */
+	function OnSaveItems(&$event)
+	{
+		$tmp = $this->Application->RecallVar('priority_changes'.$this->Application->GetVar('m_wid'));
+		$changes = $tmp ? unserialize($tmp) : array();
+
+		$priority_helper =& $this->Application->recallObject('PriorityHelper');
+		/* @var $priority_helper kPriorityHelper */
+
+		list ($constrain, $joins) = $this->getConstrainInfo($event);
+		$ids = $priority_helper->updatePriorities($event->MasterEvent, $changes, $event->MasterEvent->getEventParam('ids'), $constrain, $joins);
+
+		if ($ids) {
+			$priority_helper->massUpdateChanged($event->MasterEvent->Prefix, $ids);
+		}
+	}
+
+	function OnItemCreate(&$event)
+	{
+		$obj =& $event->MasterEvent->getObject();
+		if ($obj->GetDBField('Priority') == 0) {
+			$priority_helper =& $this->Application->recallObject('PriorityHelper');
+			/* @var $priority_helper kPriorityHelper */
+
+			list ($constrain, $joins) = $this->getConstrainInfo($event);
+			$priority_helper->preparePriorities($event->MasterEvent, true, $constrain, $joins);
+		}
+	}
+
+	/**
+	 * Processes OnMassMoveUp, OnMassMoveDown events
+	 *
+	 * @param kEvent $event
+	 */
+	function OnChangePriority(&$event)
+	{
+		$prefix = $this->Application->GetVar('priority_prefix');
+		$dummy_event = new kEvent( array('prefix'=>$prefix, 'name'=>'Dummy' ) );
+
+		$ids = $this->StoreSelectedIDs($dummy_event);
+
+		if ($ids) {
+			$id_field = $this->Application->getUnitOption($prefix, 'IDField');
+			$table_name = $this->Application->getUnitOption($prefix, 'TableName');
+
+			$sql = 'SELECT Priority, '.$id_field.'
+					FROM '.$table_name.'
+					WHERE '.$id_field.' IN ('.implode(',', $ids).') ORDER BY Priority DESC';
+			$priorities = $this->Conn->GetCol($sql, $id_field);
+
+			$priority_helper =& $this->Application->recallObject('PriorityHelper');
+			/* @var $priority_helper kPriorityHelper */
+
+			list ($constrain, $joins) = $this->getConstrainInfo($event);
+
+			$sql = 'SELECT IFNULL(MIN(item_table.Priority), -1)
+					FROM '.$table_name . ' item_table
+					' . $joins;
+
+			if ( $constrain ) {
+				$sql .= ' WHERE ' . $priority_helper->normalizeConstrain($constrain);
+			}
+
+			$min_priority = $this->Conn->GetOne($sql);
+
+			foreach ($ids as $id) {
+				$new_priority = $priorities[$id] + ($event->Name == 'OnMassMoveUp' ? +1 : -1);
+				if ($new_priority > -1 || $new_priority < $min_priority) {
+					continue;
+				}
+
+				$changes = Array (
+					$id	=>	Array ('old' => $priorities[$id], 'new' => $new_priority),
+				);
+
+				if ($constrain) {
+					$changes[$id]['constrain'] = $constrain;
+				}
+
+				$sql = 'UPDATE '.$table_name.'
+						SET Priority = '.$new_priority.'
+						WHERE '.$id_field.' = '.$id;
+				$this->Conn->Query($sql);
+
+				$ids = $priority_helper->updatePriorities($dummy_event, $changes, Array ($id => $id), $constrain, $joins);
+
+				if ($ids) {
+					$priority_helper->massUpdateChanged($prefix, $ids);
+				}
+			}
+		}
+
+		$this->clearSelectedIDs($dummy_event);
+	}
+
+	/**
+	 * Completely recalculates priorities in current category
+	 *
+	 * @param kEvent $event
+	 */
+	function OnRecalculatePriorities(&$event)
+	{
+		$priority_helper =& $this->Application->recallObject('PriorityHelper');
+		/* @var $priority_helper kPriorityHelper */
+
+		$prefix = $this->Application->GetVar('priority_prefix');
+		$dummy_event = new kEvent( array('prefix'=>$prefix, 'name'=>'Dummy' ) );
+
+		list ($constrain, $joins) = $this->getConstrainInfo($event);
+		$ids = $priority_helper->recalculatePriorities($dummy_event, $constrain, $joins);
+
+		if ($ids) {
+			$priority_helper->massUpdateChanged($prefix, $ids);
+		}
+	}
+
+	/**
+	 * Returns constrain for current priority calculations
+	 *
+	 * @param kEvent $event
+	 * @return Array
+	 */
+	function getConstrainInfo(&$event)
+	{
+		$constrain_event = new kEvent($event->MasterEvent->getPrefixSpecial() . ':OnGetConstrainInfo');
+		$constrain_event->setEventParam('actual_event', $event->Name);
+		$constrain_event->setEventParam('original_event', $event->MasterEvent->Name);
+		$this->Application->HandleEvent($constrain_event);
+
+		return $constrain_event->getEventParam('constrain_info');
+	}
+}