UITextField+TrailingPlaceholder.swift

import UIKit

extension UITextField {
    /// Add a trailing placeholder label that tracks the text as it changes
    func addTrailingPlaceholder(_ placeholder: String) {
        let label = UILabel()
        label.text = placeholder
        label.alpha = 0.3
        label.isHidden = true
        let container = UIView()
        container.clipsToBounds = true
        container.addSubview(label)
        addSubview(container)
        addAction(UIAction { [weak self] _ in
            guard let self = self else {
                return
            }
            label.font = self.font
            container.frame = self.textRect(forBounds: self.bounds)
            label.frame = container.bounds
            if self.window?.screen.scale == 3 {
                // Fix for slight baseline misalignment on @3x displays
                container.frame.origin.y -= 0.333
            }
            let size = (self.text ?? "").size(withAttributes: self.defaultTextAttributes)
            label.frame.origin.x = size.width
            label.isHidden = !self.hasText
        }, for: .editingChanged)
    }
}