// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/dart/element/type.dart';
import 'package:analyzer/error/listener.dart';
import 'package:analyzer/src/dart/element/type.dart';
import 'package:analyzer/src/dart/element/type_system.dart';
import 'package:analyzer/src/error/codes.dart';
import 'package:meta/meta.dart';

/// Helper for checking potentially nullable dereferences.
class NullableDereferenceVerifier {
  final TypeSystemImpl _typeSystem;
  final ErrorReporter _errorReporter;

  NullableDereferenceVerifier({
    @required TypeSystemImpl typeSystem,
    @required ErrorReporter errorReporter,
  })  : _typeSystem = typeSystem,
        _errorReporter = errorReporter;

  bool expression(Expression expression, {DartType type}) {
    if (!_typeSystem.isNonNullableByDefault) {
      return false;
    }

    type ??= expression.staticType;
    return _check(expression, type);
  }

  void report(AstNode errorNode, DartType receiverType) {
    var errorCode = receiverType == _typeSystem.typeProvider.nullType
        ? CompileTimeErrorCode.INVALID_USE_OF_NULL_VALUE
        : CompileTimeErrorCode.UNCHECKED_USE_OF_NULLABLE_VALUE;
    _errorReporter.reportErrorForNode(errorCode, errorNode);
  }

  /// If the [receiverType] is potentially nullable, report it.
  ///
  /// The [errorNode] is usually the receiver of the invocation, but if the
  /// receiver is the implicit `this`, the name of the invocation.
  bool _check(AstNode errorNode, DartType receiverType) {
    if (identical(receiverType, DynamicTypeImpl.instance) ||
        !_typeSystem.isPotentiallyNullable(receiverType)) {
      return false;
    }

    report(errorNode, receiverType);
    return true;
  }
}