import 'package:meta/meta.dart';
import 'package:moor/moor.dart';

import 'package:drift_dev/src/services/schema/verifier_impl.dart';
import 'package:sqlite3/sqlite3.dart';

abstract class SchemaVerifier {
  factory SchemaVerifier(SchemaInstantiationHelper helper) =
      VerifierImplementation;

  /// Creates a [DatabaseConnection] that contains empty tables created for the
  /// known schema [version].
  ///
  /// This is useful as a starting point for a schema migration test. You can
  /// use the [DatabaseConnection] returned to create an instance of your
  /// application database, which can then be migrated through
  /// [migrateAndValidate].
  ///
  /// If you want to insert data in a migration test, use [schemaAt].
  Future<DatabaseConnection> startAt(int version);

  /// Creates a new database and instantiates the schema with the given
  /// [version].
  ///
  /// This can be used as a starting point for a complex schema migration test
  /// to verify data integrity. You can roughly follow these steps to write such
  /// tests:
  ///
  ///  - call [schemaAt] with the starting version you want to test
  ///  - use the [InitializedSchema.rawDatabase] of the returned
  ///   [InitializedSchema] to insert data.
  ///  - connect your database class to the [InitializedSchema.connection]
  ///  - call [migrateAndValidate] with the database and your target schema
  ///    version to run a migration and verify that it yields the desired schema
  ///    when done.
  ///  - run select statements on your database to verify that the data from
  ///    step 2 hasn't been affected by the migration.
  ///
  /// If you only want to verify the schema without data, using [startAt] might
  /// be easier.
  Future<InitializedSchema> schemaAt(int version);

  /// Runs a schema migration and verifies that it transforms the database into
  /// a correct state.
  ///
  /// This involves opening the [db] and calling its
  /// [GeneratedDatabase.migration] to migrate it to the latest version.
  /// Finally, the method will read from `sqlite_schema` to verify that the
  /// schema at runtime matches the expected schema version.
  ///
  /// The future completes normally if the schema migration succeeds and brings
  /// the database into the expected schema. If the comparison fails, a
  /// [SchemaMismatch] exception will be thrown.
  ///
  /// If [validateDropped] is enabled (defaults to `false`), the method also
  /// validates that no further tables, triggers or views apart from those
  /// expected exist.
  Future<void> migrateAndValidate(GeneratedDatabase db, int expectedVersion,
      {bool validateDropped = false});
}

/// The implementation of this class is generated through the `moor_generator`
/// CLI tool.
abstract class SchemaInstantiationHelper {
  GeneratedDatabase databaseForVersion(QueryExecutor db, int version);
}

/// Thrown when trying to instantiate a schema that hasn't been saved.
class MissingSchemaException implements Exception {
  /// The requested version that doesn't exist.
  final int requested;

  /// All known schema versions.
  final Iterable<int> available;

  MissingSchemaException(this.requested, this.available);

  @override
  String toString() {
    return 'Unknown schema version $requested. '
        'Known are ${available.join(', ')}.';
  }
}

/// Thrown when the actual schema differs from the expected schema.
class SchemaMismatch implements Exception {
  final String explanation;

  SchemaMismatch(this.explanation);

  @override
  String toString() {
    return 'Schema does not match\n$explanation';
  }
}

/// Contains an initialized schema with all tables, views, triggers and indices.
///
/// You can use the [connection] for your database class and the [rawDatabase]
/// to insert data before the migration.
class InitializedSchema {
  /// The raw database from the `sqlite3` package.
  ///
  /// The database contains all tables, views, triggers and indices from the
  /// requested schema. It can be used to insert data before a migration to
  /// verify that it's still intact after the migration.
  ///
  /// This database backs the [connection], so it's not necessary to close it
  /// if you're attaching a database later.
  final Database rawDatabase;

  final DatabaseConnection Function() _createConnection;

  /// A database connection with a prepared schema.
  ///
  /// You can connect your database classes to this as a starting point for
  /// migration tests.
  @Deprecated('Use newConnection instead, and store the result')
  late final DatabaseConnection connection = _createConnection();

  @internal
  InitializedSchema(this.rawDatabase, this._createConnection);

  /// Creates a new database connection.
  ///
  /// All connections returned by this method point to the [rawDatabase].
  /// However, each call to [newConnection] returns an independent connection
  /// that is considered closed from moor's point of view. This means that the
  /// [rawDatabase] can be used by multiple generated database classes that
  /// can independently be opened and closed, albeit not simultaneously.
  ///
  /// ## Example
  ///
  /// When generating the schema helpers with the `--data-classes` and the
  /// `--companions` command-line flags, this method can be used to create moor
  /// databases inserting data at specific versions:
  ///
  /// ```dart
  /// import 'generated/schema.dart';
  /// import 'generated/schema_v1.dart' as v1;
  /// import 'generated/schema_v2.dart' as v2;
  ///
  /// test('data integrity from v1 to v2', () async {
  ///   final verifier = SchemaVerifier(GeneratedHelper());
  ///   final schema = await verifier.schemaAt(1);
  ///
  ///   // Insert some data from the view of the old database on an independent
  ///   // connection!
  ///   final oldDb = v1.DatabaseAtV1.connect(schema.newConnection());
  ///   await oldDb.into(oldDb.users).insert(v1.UsersCompanion(id: Value(1)));
  ///   await oldDb.close();
  ///
  ///   // Run the migration on the real database class from your app
  ///   final dbForMigration = Database(schema.newConnection());
  ///   await verifier.migrateAndValidate(dbForMigration, 2);
  ///   await dbForMigration.close();
  ///
  ///   // Make sure the user is still here with a new database at v2
  ///   final checkDb = v2.DatabaseAtV2.connect(schema.newConnection());
  ///   final user = await checkDb.select(checkDb.users).getSingle();
  ///   expect(user.id, 1);
  ///   expect(user.name, 'default name from migration');
  ///   await checkDb.close();
  /// });
  /// ```
  DatabaseConnection newConnection() => _createConnection();
}