Link ID refactoring

Links now use an incremental unique numeric identifier.
    This ID is persistent and must never change.

    ArrayAccess is used to match the link ID with the array keys (see the comment in LinkDB for more details)

    Key 'created' added, with creation date as a DateTime object. 'updated' is now also a DateTime.

application/LinkDB.php

@@ -6,15 +6,15 @@
  *
  * Example:
  *    $myLinks = new LinkDB();
- *    echo $myLinks['20110826_161819']['title'];
+ *    echo $myLinks[350]['title'];
  *    foreach ($myLinks as $link)
  *       echo $link['title'].' at url '.$link['url'].'; description:'.$link['description'];
  *
  * Available keys:
+ *  - id:       primary key, incremental integer identifier (persistent)
  *  - description: description of the entry
- *  - linkdate: creation date of this entry, format: YYYYMMDD_HHMMSS
+ *  - created:  creation date of this entry, DateTime object.
- *              (e.g.'20110914_192317')
+ *  - updated:  last modification date of this entry, DateTime object.
- *  - updated:  last modification date of this entry, format: YYYYMMDD_HHMMSS
  *  - private:  Is this link private? 0=no, other value=yes
  *  - tags:     tags attached to this entry (separated by spaces)
  *  - title     Title of the link
@@ -27,6 +27,19 @@
  *  - ArrayAccess: behaves like an associative array;
  *  - Countable:   there is a count() method;
  *  - Iterator:    usable in foreach () loops.
+ *
+ * ID mechanism:
+ *   ArrayAccess is implemented in a way that will allow to access a link
+ *   with the unique identifier ID directly with $link[ID].
+ *   Note that it's not the real key of the link array attribute.
+ *   This mechanism is in place to have persistent link IDs,
+ *   even though the internal array is reordered by date.
+ *   Example:
+ *     - DB: link #1 (2010-01-01) link #2 (2016-01-01)
+ *     - Order: #2 #1
+ *     - Import links containing: link #3 (2013-01-01)
+ *     - New DB: link #1 (2010-01-01) link #2 (2016-01-01) link #3 (2013-01-01)
+ *     - Real order: #2 #3 #1
  */
 class LinkDB implements Iterator, Countable, ArrayAccess
 {
@@ -47,11 +60,17 @@ class LinkDB implements Iterator, Countable, ArrayAccess
     //  - value: associative array (keys: title, description...)
     private $links;
 
-    // List of all recorded URLs (key=url, value=linkdate)
+    // List of all recorded URLs (key=url, value=link offset)
-    // for fast reserve search (url-->linkdate)
+    // for fast reserve search (url-->link offset)
     private $urls;
 
-    // List of linkdate keys (for the Iterator interface implementation)
+    /**
+     * @var array List of all links IDS mapped with their array offset.
+     *            Map: id->offset.
+     */
+    protected $ids;
+
+    // List of offset keys (for the Iterator interface implementation)
     private $keys;
 
     // Position in the $this->keys array (for the Iterator interface)
@@ -121,14 +140,26 @@ public function offsetSet($offset, $value)
         if (!$this->loggedIn) {
             die('You are not authorized to add a link.');
         }
-        if (empty($value['linkdate']) || empty($value['url'])) {
+        if (!isset($value['id']) || empty($value['url'])) {
-            die('Internal Error: A link should always have a linkdate and URL.');
+            die('Internal Error: A link should always have an id and URL.');
         }
-        if (empty($offset)) {
+        if ((! empty($offset) && ! is_int($offset)) || ! is_int($value['id'])) {
-            die('You must specify a key.');
+            die('You must specify an integer as a key.');
+        }
+        if (! empty($offset) && $offset !== $value['id']) {
+            die('Array offset and link ID must be equal.');
+        }
+
+        // If the link exists, we reuse the real offset, otherwise new entry
+        $existing = $this->getLinkOffset($offset);
+        if ($existing !== null) {
+            $offset = $existing;
+        } else {
+            $offset = count($this->links);
         }
         $this->links[$offset] = $value;
-        $this->urls[$value['url']]=$offset;
+        $this->urls[$value['url']] = $offset;
+        $this->ids[$value['id']] = $offset;
     }
 
     /**
@@ -136,7 +167,7 @@ public function offsetSet($offset, $value)
      */
     public function offsetExists($offset)
     {
-        return array_key_exists($offset, $this->links);
+        return array_key_exists($this->getLinkOffset($offset), $this->links);
     }
 
     /**
@@ -148,9 +179,11 @@ public function offsetUnset($offset)
             // TODO: raise an exception
             die('You are not authorized to delete a link.');
         }
-        $url = $this->links[$offset]['url'];
+        $realOffset = $this->getLinkOffset($offset);
+        $url = $this->links[$realOffset]['url'];
         unset($this->urls[$url]);
-        unset($this->links[$offset]);
+        unset($this->ids[$realOffset]);
+        unset($this->links[$realOffset]);
     }
 
     /**
@@ -158,7 +191,8 @@ public function offsetUnset($offset)
      */
     public function offsetGet($offset)
     {
-        return isset($this->links[$offset]) ? $this->links[$offset] : null;
+        $realOffset = $this->getLinkOffset($offset);
+        return isset($this->links[$realOffset]) ? $this->links[$realOffset] : null;
     }
 
     /**
@@ -166,7 +200,7 @@ public function offsetGet($offset)
      */
     public function current()
     {
-        return $this->links[$this->keys[$this->position]];
+        return $this[$this->keys[$this->position]];
     }
 
     /**
@@ -192,8 +226,7 @@ public function next()
      */
     public function rewind()
     {
-        $this->keys = array_keys($this->links);
+        $this->keys = array_keys($this->ids);
-        rsort($this->keys);
         $this->position = 0;
     }
 
@@ -219,6 +252,7 @@ private function check()
         // Create a dummy database for example
         $this->links = array();
         $link = array(
+            'id' => 1,
             'title'=>' Shaarli: the personal, minimalist, super-fast, no-database delicious clone',
             'url'=>'https://github.com/shaarli/Shaarli/wiki',
             'description'=>'Welcome to Shaarli! This is your first public bookmark. To edit or delete me, you must first login.
@@ -227,20 +261,21 @@ private function check()
 
 You use the community supported version of the original Shaarli project, by Sebastien Sauvage.',
             'private'=>0,
-            'linkdate'=> date('Ymd_His'),
+            'created'=> new DateTime(),
             'tags'=>'opensource software'
         );
-        $this->links[$link['linkdate']] = $link;
+        $this->links[1] = $link;
 
         $link = array(
+            'id' => 0,
             'title'=>'My secret stuff... - Pastebin.com',
             'url'=>'http://sebsauvage.net/paste/?8434b27936c09649#bR7XsXhoTiLcqCpQbmOpBi3rq2zzQUC5hBI7ZT1O3x8=',
             'description'=>'Shhhh! I\'m a private link only YOU can see. You can delete me too.',
             'private'=>1,
-            'linkdate'=> date('Ymd_His', strtotime('-1 minute')),
+            'created'=> new DateTime('1 minute ago'),
             'tags'=>'secretstuff'
         );
-        $this->links[$link['linkdate']] = $link;
+        $this->links[0] = $link;
 
         // Write database to disk
         $this->write();
@@ -251,7 +286,6 @@ private function check()
      */
     private function read()
     {
-
         // Public links are hidden and user not logged in => nothing to show
         if ($this->hidePublicLinks && !$this->loggedIn) {
             $this->links = array();
@@ -269,23 +303,13 @@ private function read()
                        strlen(self::$phpPrefix), -strlen(self::$phpSuffix)))));
         }
 
-        // If user is not logged in, filter private links.
+        $toremove = array();
-        if (!$this->loggedIn) {
+        foreach ($this->links as $key => &$link) {
-            $toremove = array();
+            if (! $this->loggedIn && $link['private'] != 0) {
-            foreach ($this->links as $link) {
+                // Transition for not upgraded databases.
-                if ($link['private'] != 0) {
+                $toremove[] = $key;
-                    $toremove[] = $link['linkdate'];
+                continue;
-                }
             }
-            foreach ($toremove as $linkdate) {
-                unset($this->links[$linkdate]);
-            }
-        }
-
-        $this->urls = array();
-        foreach ($this->links as &$link) {
-            // Keep the list of the mapping URLs-->linkdate up-to-date.
-            $this->urls[$link['url']] = $link['linkdate'];
 
             // Sanitize data fields.
             sanitizeLink($link);
@@ -307,7 +331,23 @@ private function read()
             else {
                 $link['real_url'] = $link['url'];
             }
+
+            // To be able to load links before running the update, and prepare the update
+            if (! isset($link['created'])) {
+                $link['id'] = $link['linkdate'];
+                $link['created'] = DateTime::createFromFormat('Ymd_His', $link['linkdate']);
+                if (! empty($link['updated'])) {
+                    $link['updated'] = DateTime::createFromFormat('Ymd_His', $link['updated']);
+                }
+            }
         }
+
+        // If user is not logged in, filter private links.
+        foreach ($toremove as $offset) {
+            unset($this->links[$offset]);
+        }
+
+        $this->reorder();
     }
 
     /**
@@ -430,7 +470,7 @@ public function filterSearch($filterRequest = array(), $casesensitive = false, $
             $request = '';
         }
 
-        $linkFilter = new LinkFilter($this->links);
+        $linkFilter = new LinkFilter($this);
         return $linkFilter->filter($type, $request, $casesensitive, $privateonly);
     }
 
@@ -467,12 +507,64 @@ public function allTags()
     public function days()
     {
         $linkDays = array();
-        foreach (array_keys($this->links) as $day) {
+        foreach ($this->links as $link) {
-            $linkDays[substr($day, 0, 8)] = 0;
+            $linkDays[$link['created']->format('Ymd')] = 0;
         }
         $linkDays = array_keys($linkDays);
         sort($linkDays);
 
         return $linkDays;
     }
+
+    /**
+     * Reorder links by creation date (newest first).
+     *
+     * Also update the urls and ids mapping arrays.
+     *
+     * @param string $order ASC|DESC
+     */
+    public function reorder($order = 'DESC')
+    {
+        $order = $order === 'ASC' ? -1 : 1;
+        // Reorder array by dates.
+        usort($this->links, function($a, $b) use ($order) {
+            return $a['created'] < $b['created'] ? 1 * $order : -1 * $order;
+        });
+
+        $this->urls = array();
+        $this->ids = array();
+        foreach ($this->links as $key => $link) {
+            $this->urls[$link['url']] = $key;
+            $this->ids[$link['id']] = $key;
+        }
+    }
+
+    /**
+     * Return the next key for link creation.
+     * E.g. If the last ID is 597, the next will be 598.
+     *
+     * @return int next ID.
+     */
+    public function getNextId()
+    {
+        if (!empty($this->ids)) {
+            return max(array_keys($this->ids)) + 1;
+        }
+        return 0;
+    }
+
+    /**
+     * Returns a link offset in links array from its unique ID.
+     *
+     * @param int $id Persistent ID of a link.
+     *
+     * @return int Real offset in local array, or null if doesn't exists.
+     */
+    protected function getLinkOffset($id)
+    {
+        if (isset($this->ids[$id])) {
+            return $this->ids[$id];
+        }
+        return null;
+    }
 }