import SwiftUI
import UIKit
import Combine

extension View {
    /// Puts a Done button above the keyboard.
    ///
    /// The numeric fields (Settings → Average fuel economy and Typical
    /// fill-up, and the Worth the Drive fill-up box in the station list) use
    /// `.decimalPad`, which has NO Return key. Without this there is no way to
    /// dismiss the keyboard once such a field is tapped, and a
    /// `TextField(value:format:)` only commits the typed value when editing
    /// ends — so the number never stuck either.
    ///
    /// WHY IT IS DRAWN HERE RATHER THAN AS `.toolbar(placement: .keyboard)`:
    /// the keyboard-toolbar form is device-dependent. The same build showed the
    /// Done button on the iPhone 15 Pro and NOT on the iPhone SE (both iOS
    /// 27.0.1, same install, same binary), leaving the SE with no way to
    /// dismiss or commit a numeric field. Drawing the bar in the screen's own
    /// bottom safe area renders identically on every device, so the accessibility
    /// of the numeric fields no longer depends on the accessory view appearing.
    ///
    /// Apply ONCE per screen, to the list or form containing the fields: any
    /// keyboard on that screen shows the bar, so attaching it to each field
    /// would stack several Done buttons.
    ///
    /// - Parameter action: clears the screen's focus state. Prefer this where a
    ///   `@FocusState` exists; the default resigns the current first responder,
    ///   which works for fields inside subviews that have no focus binding (the
    ///   fill-up box in the station list is one).
    func keyboardDoneButton(action: (() -> Void)? = nil) -> some View {
        modifier(KeyboardDoneBar(action: action))
    }
}

/// Shows a Done bar while a keyboard is up on this screen.
///
/// Visibility comes from the keyboard notifications rather than a `@FocusState`
/// so the bar also works for fields inside subviews that have no focus binding.
private struct KeyboardDoneBar: ViewModifier {
    let action: (() -> Void)?

    @State private var isKeyboardVisible = false

    func body(content: Content) -> some View {
        content
            .safeAreaInset(edge: .bottom, spacing: 0) {
                if isKeyboardVisible {
                    HStack {
                        Spacer()
                        Button("Done") {
                            if let action {
                                action()
                            } else {
                                UIApplication.shared.sendAction(
                                    #selector(UIResponder.resignFirstResponder),
                                    to: nil,
                                    from: nil,
                                    for: nil
                                )
                            }
                            isKeyboardVisible = false
                        }
                        .font(.body.weight(.semibold))
                    }
                    .padding(.horizontal, 20)
                    .padding(.vertical, 10)
                    .frame(maxWidth: .infinity)
                    .background(.bar)
                }
            }
            .onReceive(NotificationCenter.default.publisher(for: UIResponder.keyboardWillShowNotification)) { _ in
                isKeyboardVisible = true
            }
            .onReceive(NotificationCenter.default.publisher(for: UIResponder.keyboardWillHideNotification)) { _ in
                isKeyboardVisible = false
            }
    }
}