# frozen_string_literal: true

require "active_support/core_ext/object/deep_dup"

module ActionDispatch # :nodoc:
  # = Action Dispatch \PermissionsPolicy
  #
  # Configures the HTTP
  # {Feature-Policy}[https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Feature-Policy]
  # response header to specify which browser features the current document and
  # its iframes can use.
  #
  # Example global policy:
  #
  #   Rails.application.config.permissions_policy do |policy|
  #     policy.camera      :none
  #     policy.gyroscope   :none
  #     policy.microphone  :none
  #     policy.usb         :none
  #     policy.fullscreen  :self
  #     policy.payment     :self, "https://secure.example.com"
  #   end
  #
  # The Feature-Policy header has been renamed to Permissions-Policy.
  # The Permissions-Policy requires a different implementation and isn't
  # yet supported by all browsers. To avoid having to rename this
  # middleware in the future we use the new name for the middleware but
  # keep the old header name and implementation for now.
  class PermissionsPolicy
    class Middleware
      def initialize(app)
        @app = app
      end

      def call(env)
        _, headers, _ = response = @app.call(env)

        return response if policy_present?(headers)

        request = ActionDispatch::Request.new(env)

        if policy = request.permissions_policy
          headers[ActionDispatch::Constants::FEATURE_POLICY] = policy.build(request.controller_instance)
        end

        if policy_empty?(policy)
          headers.delete(ActionDispatch::Constants::FEATURE_POLICY)
        end

        response
      end

      private
        def policy_present?(headers)
          headers[ActionDispatch::Constants::FEATURE_POLICY]
        end

        def policy_empty?(policy)
          policy&.directives&.empty?
        end
    end

    module Request
      POLICY = "action_dispatch.permissions_policy"

      def permissions_policy
        get_header(POLICY)
      end

      def permissions_policy=(policy)
        set_header(POLICY, policy)
      end
    end

    MAPPINGS = {
      self: "'self'",
      none: "'none'",
    }.freeze

    # List of available permissions can be found at
    # https://github.com/w3c/webappsec-permissions-policy/blob/main/features.md#policy-controlled-features
    DIRECTIVES = {
      accelerometer:        "accelerometer",
      ambient_light_sensor: "ambient-light-sensor",
      autoplay:             "autoplay",
      camera:               "camera",
      encrypted_media:      "encrypted-media",
      fullscreen:           "fullscreen",
      geolocation:          "geolocation",
      gyroscope:            "gyroscope",
      hid:                  "hid",
      idle_detection:       "idle_detection",
      magnetometer:         "magnetometer",
      microphone:           "microphone",
      midi:                 "midi",
      payment:              "payment",
      picture_in_picture:   "picture-in-picture",
      screen_wake_lock:     "screen-wake-lock",
      serial:               "serial",
      sync_xhr:             "sync-xhr",
      usb:                  "usb",
      web_share:            "web-share",
    }.freeze

    private_constant :MAPPINGS, :DIRECTIVES

    attr_reader :directives

    def initialize
      @directives = {}
      yield self if block_given?
    end

    def initialize_copy(other)
      @directives = other.directives.deep_dup
    end

    DIRECTIVES.each do |name, directive|
      define_method(name) do |*sources|
        if sources.first
          @directives[directive] = apply_mappings(sources)
        else
          @directives.delete(directive)
        end
      end
    end

    %w[speaker vibrate vr].each do |directive|
      define_method(directive) do |*sources|
        ActionDispatch.deprecator.warn(<<~MSG)
          The `#{directive}` permissions policy directive is deprecated
          and will be removed in Rails 7.2.

          There is no browser support for this directive, and no plan
          for browser support in the future. You can just remove this
          directive from your application.
        MSG

        if sources.first
          @directives[directive] = apply_mappings(sources)
        else
          @directives.delete(directive)
        end
      end
    end

    def build(context = nil)
      build_directives(context).compact.join("; ")
    end

    private
      def apply_mappings(sources)
        sources.map do |source|
          case source
          when Symbol
            apply_mapping(source)
          when String, Proc
            source
          else
            raise ArgumentError, "Invalid HTTP permissions policy source: #{source.inspect}"
          end
        end
      end

      def apply_mapping(source)
        MAPPINGS.fetch(source) do
          raise ArgumentError, "Unknown HTTP permissions policy source mapping: #{source.inspect}"
        end
      end

      def build_directives(context)
        @directives.map do |directive, sources|
          if sources.is_a?(Array)
            "#{directive} #{build_directive(sources, context).join(' ')}"
          elsif sources
            directive
          else
            nil
          end
        end
      end

      def build_directive(sources, context)
        sources.map { |source| resolve_source(source, context) }
      end

      def resolve_source(source, context)
        case source
        when String
          source
        when Symbol
          source.to_s
        when Proc
          if context.nil?
            raise RuntimeError, "Missing context for the dynamic permissions policy source: #{source.inspect}"
          else
            context.instance_exec(&source)
          end
        else
          raise RuntimeError, "Unexpected permissions policy source: #{source.inspect}"
        end
      end
  end
end