A zero-dependency Ruby on Rails implementation to redirect users to the Apple App Store or Google Play Store using User-Agent matching.

downloads_controller.rb

class DownloadsController < ApplicationController
  APP_STORE_URL  = "https://apps.apple.com/us/app/google/id284815942".freeze
  PLAY_STORE_URL = "https://play.google.com/store/apps/details?id=com.google.android.googlequicksearchbox".freeze

  def show
    if apple_device?
      redirect_to APP_STORE_URL, allow_other_host: true
    else
      redirect_to PLAY_STORE_URL, allow_other_host: true
    end
  end

  private

  def apple_device?
    request.user_agent.to_s.match?(/iPhone|iPad|iPod|Mac/)
  end
end

routes.rb

Rails.application.routes.draw do
  resource :download, only: :show
end