// 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:nnbd_migration/src/conditional_discard.dart';

/// Records information about how a conditional expression or statement might
/// need to be modified.
class ConditionalModification {
  final int offset;

  final int end;

  final bool isStatement;

  final ConditionalDiscard discard;

  final _KeepNode condition;

  final _KeepNode thenStatement;

  final _KeepNode? elseStatement;

  factory ConditionalModification(AstNode node, ConditionalDiscard discard) {
    if (node is IfStatement) {
      return ConditionalModification._(
          node.offset,
          node.end,
          true,
          discard,
          _KeepNode(node.condition),
          _KeepNode(node.thenStatement),
          node.elseStatement == null ? null : _KeepNode(node.elseStatement!));
    } else if (node is IfElement) {
      return ConditionalModification._(
          node.offset,
          node.end,
          node is Statement,
          discard,
          _KeepNode(node.condition),
          _KeepNode(node.thenElement),
          node.elseElement == null ? null : _KeepNode(node.elseElement!));
    } else {
      throw UnimplementedError('TODO(paulberry)');
    }
  }

  ConditionalModification._(this.offset, this.end, this.isStatement,
      this.discard, this.condition, this.thenStatement, this.elseStatement);
}

/// Helper object used by [ConditionalModification] to keep track of AST nodes
/// within the conditional expression.
class _KeepNode {
  final int offset;

  final int end;

  final bool isExpression;

  factory _KeepNode(AstNode node) {
    int offset = node.offset;
    int end = node.end;
    if (node is Block && node.statements.isNotEmpty) {
      offset = node.statements.beginToken!.offset;
      end = node.statements.endToken!.end;
    }
    return _KeepNode._(offset, end, node is Expression);
  }

  _KeepNode._(this.offset, this.end, this.isExpression);
}