View+Extensions.swift

//
//  View+Extensions.swift
//  my41
//
//  Created by Miroslav Perovic on 6.1.21..
//  Copyright © 2021 iPera. All rights reserved.
//

import SwiftUI

struct GeometryPreferenceReader<K: PreferenceKey, V> where K.Value == V {
	let key: K.Type
	let value: (GeometryProxy) -> V
}

extension GeometryPreferenceReader: ViewModifier {
	func body(content: Content) -> some View {
		content
			.background(GeometryReader {
				Color.clear.preference(key: self.key, value: self.value($0))
			})
	}
}

protocol Preference {}

struct AppendValue<T: Preference>: PreferenceKey {
	static var defaultValue: [CGFloat] { [] }
	static func reduce(value: inout Value, nextValue: () -> Value) {
		value.append(contentsOf: nextValue())
	}
	typealias Value = [CGFloat]
}

extension View {
	func assignMaxPreference<K: PreferenceKey>(
		for key: K.Type,
		to binding: Binding<CGFloat?>) -> some View where K.Value == [CGFloat] {
		
		return self.onPreferenceChange(key.self) { prefs in
			let maxPref = prefs.reduce(0, max)
			if maxPref > 0 {
				// only set value if > 0 to avoid pinning sizes to zero
				binding.wrappedValue = maxPref
			}
		}
	}
	
	func read<K: PreferenceKey, V>(_ preference: GeometryPreferenceReader<K, V>) -> some View {
		modifier(preference)
	}
}