App: Add option to restore database when a DB error occurs at startup

Elwig/Helpers/AppDbUpdater.cs

@@ -14,10 +14,17 @@ namespace Elwig.Helpers {
         private static int VersionOffset = 0;
 
         public static async Task<Version> CheckDb() {
+            if (!File.Exists(App.Config.DatabaseFile))
+                throw new FileNotFoundException($"Die Datei \"{App.Config.DatabaseFile}\" exisitiert nicht");
+
             long? applId, schemaVers;
             using (var cnx = await AppDbContext.ConnectAsync()) {
+
+                await cnx.QuickCheck();
+
                 applId = (long?)await cnx.ExecuteScalar("PRAGMA application_id") ?? 0;
-                if (applId != 0x454C5747) throw new Exception($"Invalid application_id in database (0x{applId:X08})");
+                if (applId != 0x454C5747)
+                    throw new FileFormatException($"Invalid application_id in database (0x{applId:X08})");
 
                 schemaVers = (long?)await cnx.ExecuteScalar("PRAGMA schema_version") ?? 0;
                 VersionOffset = (int)(schemaVers % 100);
@@ -76,16 +83,16 @@ namespace Elwig.Helpers {
             try {
                 using var cnx = await AppDbContext.ConnectAsync();
                 await cnx.ExecuteBatch("PRAGMA locking_mode = EXCLUSIVE");
+
+                await cnx.IntegrityCheck();
+                await cnx.ForeignKeyCheck();
+
                 foreach (var script in toExecute) {
                     await cnx.ExecuteEmbeddedScript(asm, script);
                 }
 
-                var violations = await cnx.ForeignKeyCheck();
-                if (violations.Length > 0) {
-                    throw new Exception($"Foreign key violations ({violations.Length}):\n" + string.Join("\n", violations
-                        .Take(50)
-                        .Select(v => $"{v.Table} - {v.RowId} - {v.Parent} - {v.FkId}")));
-                }
+                await cnx.IntegrityCheck();
+                await cnx.ForeignKeyCheck();
 
                 await cnx.ExecuteBatch("VACUUM");
                 await cnx.ExecuteBatch($"PRAGMA schema_version = {toVersion * 100 + VersionOffset}");