SwiftUI+KeyboardAvoidance.swift

/**
 Adapted from here:
 https://www.vadimbulavin.com/how-to-move-swiftui-view-when-keyboard-covers-text-field/

 Use these publishers to know when the keyboard is about to hide or show.
 As an example, you can use this to scroll a ScrollView automatically after
 the keyboard shows, using the timing information provided here.
 */

import Combine
import SwiftUI

extension Publishers {
    static var keyboardWillChange: AnyPublisher<(height: CGFloat, animationDuration: TimeInterval), Never> {
        let willShow = NotificationCenter.default.publisher(for: UIApplication.keyboardWillShowNotification)
            .map {
                (height: $0.keyboardHeight, animationDuration: $0.keyboardAnimationDuration)
            }

        let willHide = NotificationCenter.default.publisher(for: UIApplication.keyboardWillHideNotification)
            .map {
                (height: CGFloat(0), animationDuration: $0.keyboardAnimationDuration)
            }

        return MergeMany(willShow, willHide)
            .eraseToAnyPublisher()
    }
}

extension Notification {
    var keyboardHeight: CGFloat {
        return (userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect)?.height ?? 0
    }
    var keyboardAnimationDuration: TimeInterval {
        return (userInfo?[UIResponder.keyboardAnimationDurationUserInfoKey] as? TimeInterval) ?? 0
    }
}