feat: add pre-flight checks before backup starts (#67)

Validate backup prerequisites before creating any record, catching
common issues early with clear messages instead of failing mid-backup.

Pre-flight checks:
- Required PHP extensions (zip, pdo, pdo_mysql, mbstring, curl)
- Backup directory exists and is writable
- Sufficient disk space (last backup size + 20% buffer, skipped if
  no previous backup exists)
- No other backup already running for this profile
- Excluded tables exist in database (warns on missing)
- Remote storage credentials minimally configured (FTP/S3/GDrive)

Errors block the backup; warnings are logged and displayed but allow
the backup to proceed. Integrated into both BackupEngine::run() and
SteppedBackupEngine::init() before any record is inserted.

UI: AJAX init response includes warnings array, displayed in the
stepped backup progress modal.

Closes #67

source/packages/com_mokosuitebackup/src/Controller/BackupsController.php

@@ -49,6 +49,13 @@ class BackupsController extends AdminController
 		$engine = new BackupEngine();
 		$result = $engine->run($profileId, $description, 'backend');
 
+		// Surface preflight warnings as Joomla messages
+		if (!empty($result['warnings'])) {
+			foreach ($result['warnings'] as $warning) {
+				$this->app->enqueueMessage($warning, 'warning');
+			}
+		}
+
 		if ($result['success']) {
 			$this->setMessage($result['message']);
 		} else {

source/packages/com_mokosuitebackup/src/Engine/BackupEngine.php

@@ -32,16 +32,21 @@ class BackupEngine
 	 */
 	public function run(int $profileId, string $description, string $origin = 'backend'): array
 	{
+		// Run pre-flight checks before creating any backup record
+		$preflight = new PreflightCheck();
+		$preflightResult = $preflight->run($profileId);
+
+		if (!$preflightResult['pass']) {
+			return [
+				'success'  => false,
+				'message'  => 'Pre-flight failed: ' . implode('; ', $preflightResult['errors']),
+				'warnings' => $preflightResult['warnings'],
+			];
+		}
+
 		// Override PHP limits for long-running backup operations
 		$this->overridePhpLimits();
 
-		// Verify required extensions
-		$extCheck = $this->checkRequiredExtensions();
-
-		if ($extCheck !== true) {
-			return ['success' => false, 'message' => $extCheck];
-		}
-
 		$db = Factory::getDbo();
 
 		// Load profile
@@ -56,6 +61,11 @@ class BackupEngine
 			return ['success' => false, 'message' => 'Profile not found: ' . $profileId];
 		}
 
+		// Log any preflight warnings
+		foreach ($preflightResult['warnings'] as $warning) {
+			$this->log('PREFLIGHT WARNING: ' . $warning);
+		}
+
 		// Read settings directly from profile columns
 		$excludeDirs   = BackupDirectory::parseNewlineList($profile->exclude_dirs ?? '');
 		$excludeFiles  = BackupDirectory::parseNewlineList($profile->exclude_files ?? '');

source/packages/com_mokosuitebackup/src/Engine/PreflightCheck.php

@@ -0,0 +1,288 @@
+<?php
+
+/**
+ * @package     MokoSuiteBackup
+ * @subpackage  com_mokosuitebackup
+ * @author      Moko Consulting <hello@mokoconsulting.tech>
+ * @copyright   Copyright (C) 2026 Moko Consulting. All rights reserved.
+ * @license     GNU General Public License version 3 or later; see LICENSE
+ *
+ * Pre-flight validation for backup operations.
+ *
+ * Runs before any backup record is created, catching problems early
+ * with clear messages instead of failing mid-backup. Returns a result
+ * with errors (blockers) and warnings (informational).
+ */
+
+namespace Joomla\Component\MokoSuiteBackup\Administrator\Engine;
+
+defined('_JEXEC') or die;
+
+use Joomla\CMS\Factory;
+use Joomla\Component\MokoSuiteBackup\Administrator\Utility\BackupDirectory;
+
+class PreflightCheck
+{
+	/** @var string[] Fatal issues that prevent backup from starting */
+	private array $errors = [];
+
+	/** @var string[] Non-fatal issues the user should know about */
+	private array $warnings = [];
+
+	/**
+	 * Run all pre-flight checks for a backup profile.
+	 *
+	 * @param   int  $profileId  Profile to validate
+	 *
+	 * @return  array{pass: bool, errors: string[], warnings: string[]}
+	 */
+	public function run(int $profileId): array
+	{
+		$db = Factory::getDbo();
+
+		// Load profile
+		$query = $db->getQuery(true)
+			->select('*')
+			->from($db->quoteName('#__mokosuitebackup_profiles'))
+			->where($db->quoteName('id') . ' = ' . $profileId);
+		$db->setQuery($query);
+		$profile = $db->loadObject();
+
+		if (!$profile) {
+			$this->errors[] = 'Profile not found: #' . $profileId;
+
+			return $this->result();
+		}
+
+		if (!$profile->published) {
+			$this->errors[] = 'Profile is unpublished: ' . $profile->title;
+
+			return $this->result();
+		}
+
+		$this->checkPhpExtensions($profile);
+		$this->checkBackupDirectory($profile);
+		$this->checkDiskSpace($profile, $db);
+		$this->checkRunningBackup($profile, $db);
+		$this->checkExcludedTables($profile, $db);
+		$this->checkRemoteCredentials($profile);
+
+		return $this->result();
+	}
+
+	/**
+	 * Check that required PHP extensions are loaded.
+	 */
+	private function checkPhpExtensions(object $profile): void
+	{
+		$required = ['pdo', 'pdo_mysql', 'mbstring'];
+
+		// ZIP is required unless using tar.gz
+		$format = $profile->archive_format ?? 'zip';
+
+		if ($format === 'zip') {
+			$required[] = 'zip';
+		}
+
+		foreach ($required as $ext) {
+			if (!extension_loaded($ext)) {
+				$this->errors[] = 'Missing required PHP extension: ext-' . $ext;
+			}
+		}
+
+		// curl is only needed for remote upload and ntfy notifications
+		$needsCurl = ($profile->remote_storage ?? 'none') !== 'none'
+			|| !empty($profile->ntfy_topic);
+
+		if ($needsCurl && !extension_loaded('curl')) {
+			$this->warnings[] = 'ext-curl is not loaded — remote upload and ntfy notifications will not work';
+		}
+	}
+
+	/**
+	 * Check that the backup directory exists and is writable.
+	 */
+	private function checkBackupDirectory(object $profile): void
+	{
+		$configuredDir = $profile->backup_dir ?: BackupDirectory::PLACEHOLDER;
+
+		// Resolve placeholders using a temporary resolver
+		$resolver   = new PlaceholderResolver($profile);
+		$resolvedDir = BackupDirectory::resolve($resolver->resolve($configuredDir));
+
+		if (BackupDirectory::hasPlaceholders($resolvedDir)) {
+			// Can't fully validate paths with unresolved placeholders
+			return;
+		}
+
+		if (!is_dir($resolvedDir)) {
+			// Try to create it
+			if (!@mkdir($resolvedDir, 0755, true)) {
+				$this->errors[] = 'Backup directory does not exist and cannot be created: ' . $resolvedDir;
+
+				return;
+			}
+		}
+
+		if (!is_writable($resolvedDir)) {
+			$this->errors[] = 'Backup directory is not writable: ' . $resolvedDir;
+		}
+	}
+
+	/**
+	 * Check available disk space against the last backup size + 20% buffer.
+	 * Skipped if no previous backup exists for this profile.
+	 */
+	private function checkDiskSpace(object $profile, object $db): void
+	{
+		$configuredDir = $profile->backup_dir ?: BackupDirectory::PLACEHOLDER;
+		$resolver      = new PlaceholderResolver($profile);
+		$resolvedDir   = BackupDirectory::resolve($resolver->resolve($configuredDir));
+
+		if (BackupDirectory::hasPlaceholders($resolvedDir) || !is_dir($resolvedDir)) {
+			return;
+		}
+
+		// Find last successful backup size for this profile
+		$query = $db->getQuery(true)
+			->select($db->quoteName('total_size'))
+			->from($db->quoteName('#__mokosuitebackup_records'))
+			->where($db->quoteName('profile_id') . ' = ' . (int) $profile->id)
+			->where($db->quoteName('status') . ' = ' . $db->quote('complete'))
+			->where($db->quoteName('total_size') . ' > 0')
+			->order($db->quoteName('backupstart') . ' DESC');
+		$db->setQuery($query, 0, 1);
+		$lastSize = (int) $db->loadResult();
+
+		if ($lastSize === 0) {
+			// No previous backup — skip disk space check
+			return;
+		}
+
+		$requiredBytes = (int) ($lastSize * 1.2); // 20% buffer
+		$freeBytes     = @disk_free_space($resolvedDir);
+
+		if ($freeBytes === false) {
+			$this->warnings[] = 'Could not determine free disk space for: ' . $resolvedDir;
+
+			return;
+		}
+
+		if ($freeBytes < $requiredBytes) {
+			$freeMB    = number_format($freeBytes / 1048576, 1);
+			$neededMB  = number_format($requiredBytes / 1048576, 1);
+
+			$this->warnings[] = 'Low disk space: ' . $freeMB . ' MB free, estimated ' . $neededMB . ' MB needed'
+				. ' (based on last backup + 20% buffer)';
+		}
+	}
+
+	/**
+	 * Check if another backup is already running for this profile.
+	 */
+	private function checkRunningBackup(object $profile, object $db): void
+	{
+		$query = $db->getQuery(true)
+			->select('COUNT(*)')
+			->from($db->quoteName('#__mokosuitebackup_records'))
+			->where($db->quoteName('profile_id') . ' = ' . (int) $profile->id)
+			->where($db->quoteName('status') . ' = ' . $db->quote('running'));
+		$db->setQuery($query);
+		$running = (int) $db->loadResult();
+
+		if ($running > 0) {
+			$this->errors[] = 'Another backup is already running for profile: ' . $profile->title
+				. ' — wait for it to finish or delete the stale record';
+		}
+	}
+
+	/**
+	 * Check that excluded tables actually exist in the database.
+	 * Missing tables are warnings, not errors — the profile may have
+	 * been copied from another site or a table may have been removed.
+	 */
+	private function checkExcludedTables(object $profile, object $db): void
+	{
+		$excludeRaw = BackupDirectory::parseNewlineList($profile->exclude_tables ?? '');
+
+		if (empty($excludeRaw)) {
+			return;
+		}
+
+		$prefix    = $db->getPrefix();
+		$allTables = array_flip($db->getTableList());
+
+		foreach ($excludeRaw as $entry) {
+			// Strip :data-only / :structure-only suffixes
+			$tableName = preg_replace('/:(?:data-only|structure-only)$/', '', $entry);
+
+			// Resolve #__ prefix to real prefix
+			$realName = str_replace('#__', $prefix, $tableName);
+
+			if (!isset($allTables[$realName])) {
+				$this->warnings[] = 'Excluded table does not exist: ' . $tableName
+					. ' — it will be silently skipped during backup';
+			}
+		}
+	}
+
+	/**
+	 * Check that remote storage credentials are minimally configured.
+	 * Does not test the actual connection (too slow for preflight).
+	 */
+	private function checkRemoteCredentials(object $profile): void
+	{
+		$remote = $profile->remote_storage ?? 'none';
+
+		if ($remote === 'none') {
+			return;
+		}
+
+		switch ($remote) {
+			case 'ftp':
+				if (empty($profile->ftp_host)) {
+					$this->warnings[] = 'FTP host is not configured — remote upload will fail';
+				}
+
+				if (empty($profile->ftp_username)) {
+					$this->warnings[] = 'FTP username is not configured — remote upload will fail';
+				}
+
+				break;
+
+			case 's3':
+				if (empty($profile->s3_bucket)) {
+					$this->warnings[] = 'S3 bucket is not configured — remote upload will fail';
+				}
+
+				if (empty($profile->s3_access_key) || empty($profile->s3_secret_key)) {
+					$this->warnings[] = 'S3 credentials are not configured — remote upload will fail';
+				}
+
+				break;
+
+			case 'google_drive':
+				if (empty($profile->gdrive_client_id) || empty($profile->gdrive_client_secret)) {
+					$this->warnings[] = 'Google Drive OAuth credentials are not configured — remote upload will fail';
+				}
+
+				if (empty($profile->gdrive_refresh_token)) {
+					$this->warnings[] = 'Google Drive refresh token is missing — remote upload will fail';
+				}
+
+				break;
+		}
+	}
+
+	/**
+	 * Build the result array.
+	 */
+	private function result(): array
+	{
+		return [
+			'pass'     => empty($this->errors),
+			'errors'   => $this->errors,
+			'warnings' => $this->warnings,
+		];
+	}
+}

source/packages/com_mokosuitebackup/src/Engine/SteppedBackupEngine.php

@@ -32,6 +32,18 @@ class SteppedBackupEngine
 	 */
 	public function init(int $profileId, string $description = '', string $origin = 'backend'): array
 	{
+		// Run pre-flight checks before creating any backup record
+		$preflight = new PreflightCheck();
+		$preflightResult = $preflight->run($profileId);
+
+		if (!$preflightResult['pass']) {
+			return [
+				'error'    => true,
+				'message'  => 'Pre-flight failed: ' . implode('; ', $preflightResult['errors']),
+				'warnings' => $preflightResult['warnings'],
+			];
+		}
+
 		$db = Factory::getDbo();
 
 		// Load profile
@@ -130,6 +142,11 @@ class SteppedBackupEngine
 		$session->phase = ($profile->backup_type !== 'files') ? 'database' : 'files';
 		$session->log('Backup initialized: ' . $session->description);
 		$session->log('Total steps: ' . $totalSteps . ' (tables: ' . count($session->tables) . ', file batches: ' . count($session->fileBatches) . ')');
+		// Log any preflight warnings into the session
+		foreach ($preflightResult['warnings'] as $warning) {
+			$session->log('PREFLIGHT WARNING: ' . $warning);
+		}
+
 		$session->statusMessage = 'Initialized — starting backup...';
 		$session->save();
 
@@ -138,6 +155,7 @@ class SteppedBackupEngine
 			'phase'      => $session->phase,
 			'progress'   => $session->getProgress(),
 			'message'    => $session->statusMessage,
+			'warnings'   => $preflightResult['warnings'],
 		];
 	}
 

source/packages/com_mokosuitebackup/tmpl/backups/default.php

@@ -270,10 +270,17 @@ $listDirn  = $this->escape($this->state->get('list.direction'));
 
 			if (initResult.error) {
 				updateProgress(0, 'ERROR: ' + initResult.message, 'failed');
-				setTimeout(hideModal, 3000);
+				setTimeout(hideModal, 5000);
 				return;
 			}
 
+			// Show preflight warnings if any
+			if (initResult.warnings && initResult.warnings.length > 0) {
+				var warningEl = document.getElementById('mb-phase');
+				warningEl.textContent = 'Warnings: ' + initResult.warnings.join('; ');
+				warningEl.style.color = '#856404';
+			}
+
 			const sessionId = initResult.session_id;
 			updateProgress(initResult.progress, initResult.message, initResult.phase);
 

source/packages/com_mokosuitebackup/tmpl/dashboard/default.php

@@ -255,10 +255,17 @@ document.querySelectorAll('.mb-tile').forEach(function(tile) {
 
 			if (initResult.error) {
 				updateProgress(0, 'ERROR: ' + initResult.message, 'failed');
-				setTimeout(hideModal, 3000);
+				setTimeout(hideModal, 5000);
 				return;
 			}
 
+			// Show preflight warnings if any
+			if (initResult.warnings && initResult.warnings.length > 0) {
+				var warningEl = document.getElementById('mb-phase');
+				warningEl.textContent = 'Warnings: ' + initResult.warnings.join('; ');
+				warningEl.style.color = '#856404';
+			}
+
 			const sessionId = initResult.session_id;
 			updateProgress(initResult.progress, initResult.message, initResult.phase);