InvertIfCondition.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2026 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#if compiler(>=6)
public import SwiftSyntax
#else
import SwiftSyntax
#endif

/// Inverts a negated `if` condition and swaps the branches.
///
/// ## Before
///
/// ```swift
/// if !x {
///   foo()
/// } else {
///   bar()
/// }
/// ```
///
/// ## After
///
/// ```swift
/// if x {
///   bar()
/// } else {
///   foo()
/// }
/// ```
public struct InvertIfCondition: SyntaxRefactoringProvider {
  public static func refactor(syntax ifExpr: IfExprSyntax, in context: Void) -> IfExprSyntax {
    guard let elseBody = ifExpr.elseBody, case .codeBlock(let elseBlock) = elseBody else {
      return ifExpr
    }

    guard ifExpr.conditions.count == 1, let condition = ifExpr.conditions.first else {
      return ifExpr
    }

    guard case .expression(let expr) = condition.condition else {
      return ifExpr
    }

    guard let prefixOpExpr = expr.as(PrefixOperatorExprSyntax.self), prefixOpExpr.operator.text == "!" else {
      return ifExpr
    }

    let innerExpr = prefixOpExpr.expression.with(\.leadingTrivia, prefixOpExpr.leadingTrivia.merging(triviaOf: prefixOpExpr.operator))

    let newCondition = condition.with(\.condition, .expression(innerExpr))
    let newConditions = ifExpr.conditions.with(\.[ifExpr.conditions.startIndex], newCondition)

    let oldBody = ifExpr.body
    let oldElseBlock = elseBlock

    let newBody =
      oldElseBlock
      .with(\.leadingTrivia, oldBody.leadingTrivia)
      .with(\.trailingTrivia, oldBody.trailingTrivia)

    let newElseBody =
      oldBody
      .with(\.leadingTrivia, oldElseBlock.leadingTrivia)
      .with(\.trailingTrivia, oldElseBlock.trailingTrivia)

    return
      ifExpr
      .with(\.conditions, newConditions)
      .with(\.body, newBody)
      .with(\.elseBody, .codeBlock(newElseBody))
  }
}