Implement database schema Migrator

This commit implements the new database schema Migrator which keeps
track of the on-disk schema and the schema used by the codebase. It
tries to makes future database schema upgrades user-friendlier.

1 files changed, 43 insertions, 0 deletions

diff --git a/core/migrations.php b/core/migrations.php
new file mode 100644
index 0000000..f2c9714
--- /dev/null
+++ b/core/migrations.php
@@ -0,0 +1,43 @@
+<?php
+#===============================================================================
+# Get Migrator singleton
+#===============================================================================
+$Migrator = Application::getMigrator();
+
+#===============================================================================
+# Check for outstanding database schema migrations
+#===============================================================================
+if($Migrator->isMigrationNeeded()) {
+	@session_start();
+
+	Application::set('TEMPLATE.NAME', Application::get('ADMIN.TEMPLATE'));
+	Application::set('TEMPLATE.LANG', Application::get('ADMIN.LANGUAGE'));
+	Application::getLanguage(TRUE); // Force recreation of Language object
+
+	if(HTTP::issetPOST(['token' => Application::getSecurityToken()], 'run')) {
+		if(!$migrated = $Migrator->runMigrations()) {
+			Application::exit('CONFUSED: No migrations were performed?!');
+		}
+	}
+
+	$Template = Template\Factory::build('migration');
+	$Template->set('MIGRATION', [
+		'LIST' => $Migrator->getMigrations(),
+		'SUCCESSFUL' => $migrated ?? [],
+		'SCHEMA_VERSION' => [
+			'DATABASE' => $Migrator->getVersionFromTable(),
+			'CODEBASE' => $Migrator::CURRENT_SCHEMA_VERSION
+		],
+	]);
+
+	Application::exit($Template);
+}
+
+#===============================================================================
+# Check for an unsupported downgrade attempt
+#===============================================================================
+else if($Migrator->isDowngradeAttempt()) {
+	throw new Exception('MIGRATOR: The schema version used by *your* database is
+		higher than the schema version defined in the codebase. It is officially
+		not supported to automatically downgrade the database schema version!');
+}