// Copyright (c) 2020, 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 'dart:math';

import 'package:_fe_analyzer_shared/src/scanner/token.dart';
import 'package:analysis_server/src/services/correction/assist.dart';
import 'package:analysis_server/src/services/correction/dart/abstract_producer.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer_plugin/utilities/assist/assist.dart';
import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';

class AddNotNullAssert extends CorrectionProducer {
  @override
  AssistKind get assistKind => DartAssistKind.ADD_NOT_NULL_ASSERT;

  @override
  Future<void> compute(ChangeBuilder builder) async {
    final identifier = node;
    if (identifier is SimpleIdentifier) {
      if (identifier.parent is FormalParameter) {
        final exp = identifier.parent.thisOrAncestorMatching(
            (node) => node is FunctionExpression || node is MethodDeclaration);
        FunctionBody body;
        if (exp is FunctionExpression) {
          body = exp.body;
        } else if (exp is MethodDeclaration) {
          body = exp.body;
        }
        if (body is BlockFunctionBody) {
          var blockBody = body;
          // Check for an obvious pre-existing assertion.
          for (var statement in blockBody.block.statements) {
            if (statement is AssertStatement) {
              final condition = statement.condition;
              if (condition is BinaryExpression) {
                final leftOperand = condition.leftOperand;
                if (leftOperand is SimpleIdentifier) {
                  if (leftOperand.staticElement == identifier.staticElement &&
                      condition.operator.type == TokenType.BANG_EQ &&
                      condition.rightOperand is NullLiteral) {
                    return;
                  }
                }
              }
            }
          }

          await builder.addDartFileEdit(file, (builder) {
            final id = identifier.name;
            final prefix = utils.getNodePrefix(exp);
            final indent = utils.getIndent(1);
            // todo (pq): follow-ups:
            // 1. if the end token is on the same line as the body
            // we should add an `eol` before the assert as well.
            // 2. also, consider asking the block for the list of statements and
            // adding the statement to the beginning of the list, special casing
            // when there are no statements (or when there's a single statement
            // and the whole block is on the same line).
            var offset = min(utils.getLineNext(blockBody.beginToken.offset),
                blockBody.endToken.offset);
            builder.addSimpleInsertion(
                offset, '$prefix${indent}assert($id != null);$eol');
          });
        }
      }
    }
  }

  /// Return an instance of this class. Used as a tear-off in `AssistProcessor`.
  static AddNotNullAssert newInstance() => AddNotNullAssert();
}