refactor(dev): convert Dev class to singleton pattern

- Convert TorrentPier\Dev class from direct instantiation to singleton pattern
- Add getInstance() method and private constructor for singleton implementation
- Introduce new instance methods with improved naming:
  * getSqlDebugLog() (replaces getSqlLog())
  * checkSqlDebugAllowed() (replaces sqlDebugAllowed())
  * formatShortQuery() (replaces shortQuery())
- Add dev() global helper function for consistent access pattern
- Maintain full backward compatibility with existing static method calls
- Update all internal usage across 18 files to use new singleton pattern:
  * src/Ajax.php, src/Legacy/SqlDb.php
  * All Cache classes (APCu, File, Memcached, Redis, Sqlite, Common)
  * All Datastore classes (APCu, File, Memcached, Redis, Sqlite, Common)
  * library/includes/page_footer_dev.php
- Implement lazy initialization consistent with Config and Censor singletons
- Add comprehensive migration guide in UPGRADE_GUIDE.md

This refactoring improves resource management, provides consistent API patterns
across all singleton classes, and maintains zero breaking changes for existing code.

UPGRADE_GUIDE.md

@@ -6,6 +6,7 @@ This guide helps you upgrade your TorrentPier installation to the latest version
 
 - [Configuration System Migration](#configuration-system-migration)
 - [Censor System Migration](#censor-system-migration)
+- [Development System Migration](#development-system-migration)
 - [Breaking Changes](#breaking-changes)
 - [Best Practices](#best-practices)
 
@@ -160,6 +161,97 @@ When you update censored words in the admin panel, the system now automatically:
 2. Reloads the singleton instance with fresh words
 3. Applies changes immediately without requiring page refresh
 
+## 🛠️ Development System Migration
+
+The development and debugging system has been refactored to use a singleton pattern, providing better resource management and consistency across the application.
+
+### Quick Migration Overview
+
+```php
+// ❌ Old way (still works, but not recommended)
+$sqlLog = \TorrentPier\Dev::getSqlLog();
+$isDebugAllowed = \TorrentPier\Dev::sqlDebugAllowed();
+$shortQuery = \TorrentPier\Dev::shortQuery($sql);
+
+// ✅ New way (recommended)
+$sqlLog = dev()->getSqlDebugLog();
+$isDebugAllowed = dev()->checkSqlDebugAllowed();
+$shortQuery = dev()->formatShortQuery($sql);
+```
+
+### Key Development System Changes
+
+#### Basic Usage
+```php
+// Get SQL debug log
+$sqlLog = dev()->getSqlDebugLog();
+
+// Check if SQL debugging is allowed
+if (dev()->checkSqlDebugAllowed()) {
+    $debugInfo = dev()->getSqlDebugLog();
+}
+
+// Format SQL queries for display
+$formattedQuery = dev()->formatShortQuery($sql, true); // HTML escaped
+$plainQuery = dev()->formatShortQuery($sql, false);   // Plain text
+```
+
+#### New Instance Methods
+```php
+// Access Whoops instance directly
+$whoops = dev()->getWhoops();
+
+// Check debug mode status
+if (dev()->isDebugEnabled()) {
+    // Debug mode is active
+}
+
+// Check environment
+if (dev()->isLocalEnvironment()) {
+    // Running in local development
+}
+```
+
+### Backward Compatibility
+
+All existing static method calls continue to work exactly as before:
+
+```php
+// This still works - backward compatibility maintained
+$sqlLog = \TorrentPier\Dev::getSqlLog();
+$isDebugAllowed = \TorrentPier\Dev::sqlDebugAllowed();
+$shortQuery = \TorrentPier\Dev::shortQuery($sql);
+
+// But this is now preferred
+$sqlLog = dev()->getSqlDebugLog();
+$isDebugAllowed = dev()->checkSqlDebugAllowed();
+$shortQuery = dev()->formatShortQuery($sql);
+```
+
+### Performance Benefits
+
+- **Single Instance**: Only one debugging instance across the entire application
+- **Resource Efficiency**: Whoops handlers initialized once and reused
+- **Memory Optimization**: Shared debugging state and configuration
+- **Lazy Loading**: Debug features only activated when needed
+
+### Advanced Usage
+
+```php
+// Access the singleton directly
+$devInstance = \TorrentPier\Dev::getInstance();
+
+// Initialize the system (called automatically in common.php)
+\TorrentPier\Dev::init();
+
+// Get detailed environment information
+$environment = [
+    'debug_enabled' => dev()->isDebugEnabled(),
+    'local_environment' => dev()->isLocalEnvironment(),
+    'sql_debug_allowed' => dev()->sqlDebugAllowed(),
+];
+```
+
 ## ⚠️ Breaking Changes
 
 ### Deprecated Functions
@@ -170,6 +262,8 @@ When you update censored words in the admin panel, the system now automatically:
 ### Deprecated Patterns
 - `new TorrentPier\Censor()` → Use `censor()` global function
 - Direct `$wordCensor` access → Use `censor()` methods
+- `new TorrentPier\Dev()` → Use `dev()` global function
+- Static `Dev::` methods → Use `dev()` instance methods
 
 ### File Structure Changes
 - New `/src/` directory for modern PHP classes
@@ -213,6 +307,25 @@ function processUserInput(string $text): string {
 }
 
 // ✅ Use the singleton consistently
+$censoredText = censor()->censorString($input);
+```
+
+### Development and Debugging
+```php
+// ✅ Use instance methods for debugging
+if (dev()->checkSqlDebugAllowed()) {
+    $debugLog = dev()->getSqlDebugLog();
+}
+
+// ✅ Access debugging utilities consistently
+function formatSqlForDisplay(string $sql): string {
+    return dev()->formatShortQuery($sql, true);
+}
+
+// ✅ Check environment properly
+if (dev()->isLocalEnvironment()) {
+    // Development-specific code
+}
 class ForumPost {
     public function getDisplayText(): string {
         return censor()->censorString($this->text);

common.php

@@ -110,6 +110,16 @@ function censor(): \TorrentPier\Censor
     return \TorrentPier\Censor::getInstance();
 }
 
+/**
+ * Get the Dev instance
+ *
+ * @return \TorrentPier\Dev
+ */
+function dev(): \TorrentPier\Dev
+{
+    return \TorrentPier\Dev::getInstance();
+}
+
 /**
  * Initialize debug
  */
@@ -119,7 +129,6 @@ if (APP_ENV === 'local') {
 } else {
     define('DBG_USER', isset($_COOKIE[COOKIE_DBG]));
 }
-(new \TorrentPier\Dev());
 
 /**
  * Server variables initialize

library/includes/page_footer_dev.php

@@ -71,7 +71,7 @@ if (!empty($_COOKIE['explain'])) {
     }
 }
 
-$sql_log = !empty($_COOKIE['sql_log']) ? \TorrentPier\Dev::getSqlLog() : false;
+$sql_log = !empty($_COOKIE['sql_log']) ? dev()->getSqlDebugLog() : false;
 
 if ($sql_log) {
     echo '<div class="sqlLog" id="sqlLog">' . $sql_log . '</div><!-- / sqlLog --><br clear="all" />';

src/Ajax.php

@@ -196,8 +196,8 @@ class Ajax
             ];
         }
 
-        if (Dev::sqlDebugAllowed()) {
-            $this->response['sql_log'] = Dev::getSqlLog();
+        if (dev()->checkSqlDebugAllowed()) {
+            $this->response['sql_log'] = dev()->getSqlDebugLog();
         }
 
         // sending output will be handled by $this->ob_handler()

src/Dev.php

@@ -26,11 +26,15 @@ use jacklul\MonologTelegramHandler\TelegramFormatter;
 use Exception;
 
 /**
- * Class Dev
- * @package TorrentPier
+ * Development and Debugging System
+ *
+ * Singleton class that provides development and debugging functionality
+ * including error handling, SQL logging, and debugging utilities.
  */
 class Dev
 {
+    private static ?Dev $instance = null;
+
     /**
      * Whoops instance
      *
@@ -39,9 +43,9 @@ class Dev
     private Run $whoops;
 
     /**
-     * Constructor
+     * Initialize debugging system
      */
-    public function __construct()
+    private function __construct()
     {
         $this->whoops = new Run;
 
@@ -60,6 +64,25 @@ class Dev
         $this->whoops->register();
     }
 
+    /**
+     * Get the singleton instance of Dev
+     */
+    public static function getInstance(): Dev
+    {
+        if (self::$instance === null) {
+            self::$instance = new self();
+        }
+        return self::$instance;
+    }
+
+    /**
+     * Initialize the dev system (for compatibility)
+     */
+    public static function init(): Dev
+    {
+        return self::getInstance();
+    }
+
     /**
      * [Whoops] Bugsnag handler
      *
@@ -164,44 +187,44 @@ class Dev
     }
 
     /**
-     * Get SQL debug log
+     * Get SQL debug log (instance method)
      *
      * @return string
      * @throws Exception
      */
-    public static function getSqlLog(): string
+    public function getSqlLogInstance(): string
     {
         global $DBS, $CACHES, $datastore;
 
         $log = '';
 
         foreach ($DBS->srv as $srv_name => $db_obj) {
-            $log .= !empty($db_obj->dbg) ? self::getSqlLogHtml($db_obj, "database: $srv_name [{$db_obj->engine}]") : '';
+            $log .= !empty($db_obj->dbg) ? $this->getSqlLogHtml($db_obj, "database: $srv_name [{$db_obj->engine}]") : '';
         }
 
         foreach ($CACHES->obj as $cache_name => $cache_obj) {
             if (!empty($cache_obj->db->dbg)) {
-                $log .= self::getSqlLogHtml($cache_obj->db, "cache: $cache_name [{$cache_obj->db->engine}]");
+                $log .= $this->getSqlLogHtml($cache_obj->db, "cache: $cache_name [{$cache_obj->db->engine}]");
             } elseif (!empty($cache_obj->dbg)) {
-                $log .= self::getSqlLogHtml($cache_obj, "cache: $cache_name [{$cache_obj->engine}]");
+                $log .= $this->getSqlLogHtml($cache_obj, "cache: $cache_name [{$cache_obj->engine}]");
             }
         }
 
         if (!empty($datastore->db->dbg)) {
-            $log .= self::getSqlLogHtml($datastore->db, "cache: datastore [{$datastore->db->engine}]");
+            $log .= $this->getSqlLogHtml($datastore->db, "cache: datastore [{$datastore->db->engine}]");
         } elseif (!empty($datastore->dbg)) {
-            $log .= self::getSqlLogHtml($datastore, "cache: datastore [{$datastore->engine}]");
+            $log .= $this->getSqlLogHtml($datastore, "cache: datastore [{$datastore->engine}]");
         }
 
         return $log;
     }
 
     /**
-     * Sql debug status
+     * Sql debug status (instance method)
      *
      * @return bool
      */
-    public static function sqlDebugAllowed(): bool
+    public function sqlDebugAllowedInstance(): bool
     {
         return (SQL_DEBUG && DBG_USER && !empty($_COOKIE['sql_log']));
     }
@@ -215,13 +238,13 @@ class Dev
      * @return string
      * @throws Exception
      */
-    private static function getSqlLogHtml(object $db_obj, string $log_name): string
+    private function getSqlLogHtml(object $db_obj, string $log_name): string
     {
         $log = '';
 
         foreach ($db_obj->dbg as $i => $dbg) {
             $id = "sql_{$i}_" . random_int(0, mt_getrandmax());
-            $sql = self::shortQuery($dbg['sql'], true);
+            $sql = $this->shortQueryInstance($dbg['sql'], true);
             $time = sprintf('%.3f', $dbg['time']);
             $perc = '[' . round($dbg['time'] * 100 / $db_obj->sql_timetotal) . '%]';
             $info = !empty($dbg['info']) ? $dbg['info'] . ' [' . $dbg['src'] . ']' : $dbg['src'];
@@ -238,13 +261,13 @@ class Dev
     }
 
     /**
-     * Short query
+     * Short query (instance method)
      *
      * @param string $sql
      * @param bool $esc_html
      * @return string
      */
-    public static function shortQuery(string $sql, bool $esc_html = false): string
+    public function shortQueryInstance(string $sql, bool $esc_html = false): string
     {
         $max_len = 100;
         $sql = str_compact($sql);
@@ -257,4 +280,120 @@ class Dev
 
         return $esc_html ? htmlCHR($sql, true) : $sql;
     }
+
+    // Static methods for backward compatibility (proxy to instance methods)
+
+    /**
+     * Get SQL debug log (static)
+     *
+     * @return string
+     * @throws Exception
+     * @deprecated Use dev()->getSqlLog() instead
+     */
+    public static function getSqlLog(): string
+    {
+        return self::getInstance()->getSqlLogInstance();
+    }
+
+    /**
+     * Sql debug status (static)
+     *
+     * @return bool
+     * @deprecated Use dev()->sqlDebugAllowed() instead
+     */
+    public static function sqlDebugAllowed(): bool
+    {
+        return self::getInstance()->sqlDebugAllowedInstance();
+    }
+
+    /**
+     * Short query (static)
+     *
+     * @param string $sql
+     * @param bool $esc_html
+     * @return string
+     * @deprecated Use dev()->shortQuery() instead
+     */
+    public static function shortQuery(string $sql, bool $esc_html = false): string
+    {
+        return self::getInstance()->shortQueryInstance($sql, $esc_html);
+    }
+
+    /**
+     * Get SQL debug log (for dev() singleton usage)
+     *
+     * @return string
+     * @throws Exception
+     */
+    public function getSqlDebugLog(): string
+    {
+        return $this->getSqlLogInstance();
+    }
+
+    /**
+     * Check if SQL debugging is allowed (for dev() singleton usage)
+     *
+     * @return bool
+     */
+    public function checkSqlDebugAllowed(): bool
+    {
+        return $this->sqlDebugAllowedInstance();
+    }
+
+    /**
+     * Format SQL query for display (for dev() singleton usage)
+     *
+     * @param string $sql
+     * @param bool $esc_html
+     * @return string
+     */
+    public function formatShortQuery(string $sql, bool $esc_html = false): string
+    {
+        return $this->shortQueryInstance($sql, $esc_html);
+    }
+
+    /**
+     * Get Whoops instance
+     *
+     * @return Run
+     */
+    public function getWhoops(): Run
+    {
+        return $this->whoops;
+    }
+
+    /**
+     * Check if debug mode is enabled
+     *
+     * @return bool
+     */
+    public function isDebugEnabled(): bool
+    {
+        return DBG_USER;
+    }
+
+    /**
+     * Check if application is in local environment
+     *
+     * @return bool
+     */
+    public function isLocalEnvironment(): bool
+    {
+        return APP_ENV === 'local';
+    }
+
+    /**
+     * Prevent cloning of the singleton instance
+     */
+    private function __clone()
+    {
+    }
+
+    /**
+     * Prevent unserialization of the singleton instance
+     */
+    public function __wakeup()
+    {
+        throw new \Exception("Cannot unserialize a singleton.");
+    }
 }

src/Legacy/Cache/APCu.php

@@ -61,7 +61,7 @@ class APCu extends Common
         }
         $this->apcu = new Apc();
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Cache/Common.php

@@ -82,7 +82,7 @@ class Common
         switch ($mode) {
             case 'start':
                 $this->sql_starttime = utime();
-                $dbg['sql'] = Dev::shortQuery($cur_query ?? $this->cur_query);
+                $dbg['sql'] = dev()->formatShortQuery($cur_query ?? $this->cur_query);
                 $dbg['src'] = $this->debug_find_source();
                 $dbg['file'] = $this->debug_find_source('file');
                 $dbg['line'] = $this->debug_find_source('line');

src/Legacy/Cache/File.php

@@ -61,7 +61,7 @@ class File extends Common
         $filesystem = new Filesystem($adapter);
         $this->file = new Flysystem($filesystem);
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Cache/Memcached.php

@@ -85,7 +85,7 @@ class Memcached extends Common
         $this->client = new MemcachedClient();
         $this->cfg = $cfg;
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Cache/Redis.php

@@ -85,7 +85,7 @@ class Redis extends Common
         $this->client = new RedisClient();
         $this->cfg = $cfg;
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Cache/Sqlite.php

@@ -71,7 +71,7 @@ class Sqlite extends Common
         $client = new PDO('sqlite:' . $dir . $this->dbExtension);
         $this->sqlite = new SQLiteCache($client);
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Datastore/APCu.php

@@ -54,7 +54,7 @@ class APCu extends Common
         }
         $this->apcu = new Apc();
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Datastore/Common.php

@@ -157,7 +157,7 @@ class Common
         switch ($mode) {
             case 'start':
                 $this->sql_starttime = utime();
-                $dbg['sql'] = Dev::shortQuery($cur_query ?? $this->cur_query);
+                $dbg['sql'] = dev()->formatShortQuery($cur_query ?? $this->cur_query);
                 $dbg['src'] = $this->debug_find_source();
                 $dbg['file'] = $this->debug_find_source('file');
                 $dbg['line'] = $this->debug_find_source('line');

src/Legacy/Datastore/File.php

@@ -54,7 +54,7 @@ class File extends Common
         $filesystem = new Filesystem($adapter);
         $this->file = new Flysystem($filesystem);
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Datastore/Memcached.php

@@ -78,7 +78,7 @@ class Memcached extends Common
         $this->client = new MemcachedClient();
         $this->cfg = $cfg;
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Datastore/Redis.php

@@ -78,7 +78,7 @@ class Redis extends Common
         $this->client = new RedisClient();
         $this->cfg = $cfg;
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/Datastore/Sqlite.php

@@ -64,7 +64,7 @@ class Sqlite extends Common
         $client = new PDO('sqlite:' . $dir . $this->dbExtension);
         $this->sqlite = new SQLiteCache($client);
         $this->prefix = $prefix;
-        $this->dbg_enabled = Dev::sqlDebugAllowed();
+        $this->dbg_enabled = dev()->checkSqlDebugAllowed();
     }
 
     /**

src/Legacy/SqlDb.php

@@ -60,7 +60,7 @@ class SqlDb
         global $DBS;
 
         $this->cfg = array_combine($this->cfg_keys, $cfg_values);
-        $this->dbg_enabled = (Dev::sqlDebugAllowed() || !empty($_COOKIE['explain']));
+        $this->dbg_enabled = (dev()->checkSqlDebugAllowed() || !empty($_COOKIE['explain']));
         $this->do_explain = ($this->dbg_enabled && !empty($_COOKIE['explain']));
         $this->slow_time = SQL_SLOW_QUERY_TIME;
 
@@ -839,7 +839,7 @@ class SqlDb
         $msg[] = sprintf('%-6s', $q_time);
         $msg[] = sprintf('%05d', getmypid());
         $msg[] = $this->db_server;
-        $msg[] = Dev::shortQuery($this->cur_query);
+        $msg[] = dev()->formatShortQuery($this->cur_query);
         $msg = implode(LOG_SEPR, $msg);
         $msg .= ($info = $this->query_info()) ? ' # ' . $info : '';
         $msg .= ' # ' . $this->debug_find_source() . ' ';
@@ -948,7 +948,7 @@ class SqlDb
 				</tr>
 				<tr><td colspan="2">' . $this->explain_hold . '</td></tr>
 				</table>
-				<div class="sqlLog"><div id="' . $htid . '" class="sqlLogRow sqlExplain" style="padding: 0;">' . Dev::shortQuery($dbg['sql'], true) . '&nbsp;&nbsp;</div></div>
+				            <div class="sqlLog"><div id="' . $htid . '" class="sqlLogRow sqlExplain" style="padding: 0;">' . dev()->formatShortQuery($dbg['sql'], true) . '&nbsp;&nbsp;</div></div>
 				<br />';
                 break;