// Copyright (c) 2021, 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:analysis_server/src/services/correction/fix.dart';
import 'package:analysis_server_plugin/edit/dart/correction_producer.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
import 'package:analyzer_plugin/utilities/fixes/fixes.dart';

class AddReturnNull extends ResolvedCorrectionProducer {
  new({required super.context});

  @override
  CorrectionApplicability get applicability =>
      CorrectionApplicability.automatically;

  @override
  FixKind get fixKind => DartFixKind.addReturnNull;

  @override
  FixKind? get multiFixKind => DartFixKind.addReturnNullMulti;

  @override
  Future<void> compute(ChangeBuilder builder) async {
    Block block;

    var node = this.node;
    if (node is Block) {
      block = node;
    } else if (node is FunctionDeclaration) {
      var body = node.functionExpression.body;
      if (body is BlockFunctionBody) {
        block = body.block;
      } else {
        return;
      }
    } else if (node is MethodDeclaration) {
      var body = node.body;
      if (body is BlockFunctionBody) {
        block = body.block;
      } else {
        return;
      }
    } else {
      return;
    }
    await builder.addDartFileEdit(file, (builder) {
      var eol = builder.eol;
      int position;
      String returnStatement;
      if (block.statements.isEmpty) {
        position = block.offset + 1;
        var prefix = utils.getLinePrefix(block.offset);
        returnStatement =
            '$eol$prefix${utils.oneIndent}return null;$eol$prefix';
      } else {
        var lastStatement = block.statements.last;
        position = lastStatement.offset + lastStatement.length;
        var prefix = utils.getNodePrefix(lastStatement);
        returnStatement = '$eol${prefix}return null;';
      }

      builder.addInsertion(position, (builder) {
        builder.write(returnStatement);
      });
    });
  }
}
