todos/App/Sources/View Modifiers/OnEmptyNewlineResignFocusModifier.swift

import SwiftUI

/// A view modifier that clears text and removes focus when return is pressed on empty content.
///
/// This modifier monitors text changes and provides smart handling of newlines:
/// - Empty text is allowed normally
/// - Newlines at the end of whitespace-only text clear the field and remove focus
/// - Multi-line content with actual text is preserved normally
struct OnEmptyNewlineResignFocusModifier<Field: Hashable>: ViewModifier {

    // MARK: Properties

    /// Binding to the text being edited.
    @Binding
    private var text: String

    /// Binding to the focus state.
    private let focusState: FocusState<Field?>.Binding

    // MARK: Initializers

    /// Creates a modifier that clears text on empty newline.
    ///
    /// - Parameters:
    ///   - text: A binding to the text being edited.
    ///   - focusState: A binding to the focus state.
    init(
        text: Binding<String>,
        focusState: FocusState<Field?>.Binding
    ) {
        self._text = text
        self.focusState = focusState
    }

    // MARK: Body

    /// The content and behavior of the view modifier.
    func body(content: Content) -> some View {
        content
            .onChange(of: text) { oldValue, newValue in
                guard newValue.isEmpty == false else {
                    return
                }

                if newValue.last == .newline {
                    if newValue.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty {
                        text = ""
                        focusState.wrappedValue = nil
                    }
                }
            }
    }

}

// MARK: - View Extension

extension View {

    /// Clears the text and removes focus when return is pressed on empty content.
    ///
    /// This modifier allows users to dismiss an optional text field by pressing return
    /// when the field is empty or contains only whitespace. Multi-line content is preserved normally.
    ///
    /// - Parameters:
    ///   - focusState: A binding to the focus state.
    ///   - text: A binding to the text being edited.
    /// - Returns: A modified view with clear-on-empty behavior.
    func onEmptyNewlineResignFocus<Field: Hashable>(
        text: Binding<String>,
        from focusState: FocusState<Field?>.Binding
    ) -> some View {
        modifier(
            OnEmptyNewlineResignFocusModifier(
                text: text,
                focusState: focusState
            )
        )
    }

}