module OmniAuth
  module MultiProvider
    class Handler
      attr_reader :path_prefix, :provider_instance_path_regex, :request_path_regex,
                  :callback_path_regex, :provider_path_prefix,
                  :identity_provider_options_generator

      def initialize(path_prefix: OmniAuth.config.path_prefix,
                     identity_provider_id_regex: /\w+/,
                     &provider_generator)
        raise 'Missing provider options generator block' unless block_given?

        @path_prefix = path_prefix
        @identity_provider_options_generator = provider_generator
        @identity_provider_id_regex = identity_provider_id_regex

        # Eagerly compute these since lazy evaluation will not be threadsafe
        @provider_path_prefix = @path_prefix
        @provider_instance_path_regex = /^#{@path_prefix}\/(?<identity_provider_id>#{@identity_provider_id_regex})/
        @request_path_regex = /#{@provider_instance_path_regex}\/?$/
        @callback_path_regex = /#{@provider_instance_path_regex}\/callback\/?$/
      end

      def provider_options
        {
          request_path: method(:request_path?),
          callback_path: method(:callback_path?),
          setup: method(:setup)
        }
      end

      def setup(env)
        identity_provider_id = extract_identity_provider_id(env)
        if identity_provider_id
          strategy = env['omniauth.strategy']
          add_path_options(strategy, identity_provider_id)
          add_identity_provider_options(strategy, env, identity_provider_id)
        end
      end

      def add_path_options(strategy, identity_provider_id)
        strategy.options.merge!(
          request_path: "#{provider_path_prefix}/#{identity_provider_id}",
          callback_path: "#{provider_path_prefix}/#{identity_provider_id}/callback"
        )
      end

      def add_identity_provider_options(strategy, env, identity_provider_id)
        identity_provider_options = identity_provider_options_generator.call(identity_provider_id, env) || {}
        strategy.options.merge!(identity_provider_options)
      rescue => e
        result = strategy.fail!(:invalid_identity_provider, e)
        throw :warden, result
      end

      def request_path?(env)
        path = current_path(env)
        !!request_path_regex.match(path)
      end

      def callback_path?(env)
        path = current_path(env)
        !!callback_path_regex.match(path)
      end

      def current_path(env)
        env['PATH_INFO']
      end

      def extract_identity_provider_id(env)
        path = current_path(env)
        match = provider_instance_path_regex.match(path)
        match ? match[:identity_provider_id] : nil
      end
    end
  end
end