MDL-41674 backup: Use a trie for grouped path detection.

backup/util/xml/parser/processors/grouped_parser_processor.class.php

@@ -1,5 +1,4 @@
 <?php
-
 // This file is part of Moodle - http://moodle.org/
 //
 // Moodle is free software: you can redistribute it and/or modify
@@ -43,6 +42,22 @@ abstract class grouped_parser_processor extends simplified_parser_processor {
     protected $groupedpaths; // Paths we are requesting grouped
     protected $currentdata;  // Where we'll be acummulating data
 
+    // We create a array that stores each of the paths in a tree fashion
+    // like the filesystem.  Each element stores all the child elements that are
+    // part of a full path that builds the grouped parent path we are storing.
+    // eg Array keys are stored as follows;
+    // root => a => b
+    //      => b
+    //      => c => d
+    //           => e => f.
+    // Grouped paths here are; /a/b, /b, /c/d, /c/e/f.
+    // There are no nested parent paths, that is an enforced rule so
+    // we store an empty array to designate that the particular XML path element
+    // is in fact a grouped path.
+    // eg; $this->groupedparentprefixtree['a']['b'] = array();
+    /** @var array Search tree storing the grouped paths. */
+    protected $groupedparentprefixtree;
+
     /**
      * Keep cache of parent directory paths for XML parsing.
      * @var array
@@ -78,6 +93,18 @@ public function add_path($path, $grouped = false) {
                 throw new progressive_parser_exception('xml_grouped_child_found', $a);
             }
             $this->groupedpaths[$path] = true;
+
+            // We check earlier in the function if there is a parent that is above the path
+            // to be added so we can be sure no parent exists in the tree.
+            $patharray = explode('/', $path);
+            $currentpos = &$this->groupedparentprefixtree;
+            foreach ($patharray as $item) {
+                if (!isset($currentpos[$item])) {
+                    $currentpos[$item] = array();
+                }
+                // Update the current array position using a reference to allow in-place updates to the array.
+                $currentpos = &$currentpos[$item];
+            }
         }
         parent::add_path($path);
     }
@@ -162,13 +189,29 @@ protected function path_is_grouped($path) {
      * false if not
      */
     protected function grouped_parent_exists($path) {
-        $parentpath = $this->get_parent_path($path);
+        // Search the tree structure to find out if one of the paths
+        // above the $path is a grouped path.
+        $patharray = explode('/', $this->get_parent_path($path));
+        $groupedpath = '';
+        $currentpos = &$this->groupedparentprefixtree;
+        foreach ($patharray as $item) {
+            // When the item isn't set in the array we know
+            // there is no parent grouped path.
+            if (!isset($currentpos[$item])) {
+                return false;
+            }
+
+            // When we aren't at the start of the path, continue to build
+            // a string representation of the path that is traversed.  We will
+            // return the grouped path to the caller if we find one.
+            if ($item != '') {
+                $groupedpath .= '/'.$item;
+            }
 
-        while ($parentpath != '/') {
-            if ($this->path_is_grouped($parentpath)) {
-                return $parentpath;
+            if ($currentpos[$item] == array()) {
+                return $groupedpath;
             }
-            $parentpath = $this->get_parent_path($parentpath);
+            $currentpos = &$currentpos[$item];
         }
         return false;
     }