# frozen_string_literal: true

require "active_support/core_ext/object/try"
require "active_support/core_ext/integer/time"

module ActionController
  module ConditionalGet
    extend ActiveSupport::Concern

    include Head

    included do
      class_attribute :etaggers, default: []
    end

    module ClassMethods
      # Allows you to consider additional controller-wide information when generating an ETag.
      # For example, if you serve pages tailored depending on who's logged in at the moment, you
      # may want to add the current user id to be part of the ETag to prevent unauthorized displaying
      # of cached pages.
      #
      #   class InvoicesController < ApplicationController
      #     etag { current_user&.id }
      #
      #     def show
      #       # Etag will differ even for the same invoice when it's viewed by a different current_user
      #       @invoice = Invoice.find(params[:id])
      #       fresh_when etag: @invoice
      #     end
      #   end
      def etag(&etagger)
        self.etaggers += [etagger]
      end
    end

    # Sets the +etag+, +last_modified+, or both on the response, and renders a
    # <tt>304 Not Modified</tt> response if the request is already fresh.
    #
    # ==== Options
    #
    # [+:etag+]
    #   Sets a "weak" ETag validator on the response. See the +:weak_etag+ option.
    # [+:weak_etag+]
    #   Sets a "weak" ETag validator on the response. Requests that specify an
    #   +If-None-Match+ header may receive a <tt>304 Not Modified</tt> response
    #   if the ETag matches exactly.
    #
    #   A weak ETag indicates semantic equivalence, not byte-for-byte equality,
    #   so they're good for caching HTML pages in browser caches. They can't be
    #   used for responses that must be byte-identical, like serving +Range+
    #   requests within a PDF file.
    # [+:strong_etag+]
    #   Sets a "strong" ETag validator on the response. Requests that specify an
    #   +If-None-Match+ header may receive a <tt>304 Not Modified</tt> response
    #   if the ETag matches exactly.
    #
    #   A strong ETag implies exact equality -- the response must match byte for
    #   byte. This is necessary for serving +Range+ requests within a large
    #   video or PDF file, for example, or for compatibility with some CDNs that
    #   don't support weak ETags.
    # [+:last_modified+]
    #   Sets a "weak" last-update validator on the response. Subsequent requests
    #   that specify an +If-Modified-Since+ header may receive a <tt>304 Not Modified</tt>
    #   response if +last_modified+ <= +If-Modified-Since+.
    # [+:public+]
    #   By default the +Cache-Control+ header is private. Set this option to
    #   +true+ if you want your application to be cacheable by other devices,
    #   such as proxy caches.
    # [+:cache_control+]
    #   When given, will overwrite an existing +Cache-Control+ header. For a
    #   list of +Cache-Control+ directives, see the {article on
    #   MDN}[https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control].
    # [+:template+]
    #   By default, the template digest for the current controller/action is
    #   included in ETags. If the action renders a different template, you can
    #   include its digest instead. If the action doesn't render a template at
    #   all, you can pass <tt>template: false</tt> to skip any attempt to check
    #   for a template digest.
    #
    # ==== Examples
    #
    #   def show
    #     @article = Article.find(params[:id])
    #     fresh_when(etag: @article, last_modified: @article.updated_at, public: true)
    #   end
    #
    # This will send a <tt>304 Not Modified</tt> response if the request
    # specifies a matching ETag and +If-Modified-Since+ header. Otherwise, it
    # will render the +show+ template.
    #
    # You can also just pass a record:
    #
    #   def show
    #     @article = Article.find(params[:id])
    #     fresh_when(@article)
    #   end
    #
    # +etag+ will be set to the record, and +last_modified+ will be set to the
    # record's +updated_at+.
    #
    # You can also pass an object that responds to +maximum+, such as a
    # collection of records:
    #
    #   def index
    #     @articles = Article.all
    #     fresh_when(@articles)
    #   end
    #
    # In this case, +etag+ will be set to the collection, and +last_modified+
    # will be set to <tt>maximum(:updated_at)</tt> (the timestamp of the most
    # recently updated record).
    #
    # When passing a record or a collection, you can still specify other
    # options, such as +:public+ and +:cache_control+:
    #
    #   def show
    #     @article = Article.find(params[:id])
    #     fresh_when(@article, public: true, cache_control: { no_cache: true })
    #   end
    #
    # The above will set <tt>Cache-Control: public, no-cache</tt> in the response.
    #
    # When rendering a different template than the controller/action's default
    # template, you can indicate which digest to include in the ETag:
    #
    #   before_action { fresh_when @article, template: "widgets/show" }
    #
    def fresh_when(object = nil, etag: nil, weak_etag: nil, strong_etag: nil, last_modified: nil, public: false, cache_control: {}, template: nil)
      response.cache_control.delete(:no_store)
      weak_etag ||= etag || object unless strong_etag
      last_modified ||= object.try(:updated_at) || object.try(:maximum, :updated_at)

      if strong_etag
        response.strong_etag = combine_etags strong_etag,
          last_modified: last_modified, public: public, template: template
      elsif weak_etag || template
        response.weak_etag = combine_etags weak_etag,
          last_modified: last_modified, public: public, template: template
      end

      response.last_modified = last_modified if last_modified
      response.cache_control[:public] = true if public
      response.cache_control.merge!(cache_control)

      head :not_modified if request.fresh?(response)
    end

    # Sets the +etag+ and/or +last_modified+ on the response and checks them
    # against the request. If the request doesn't match the provided options, it
    # is considered stale, and the response should be rendered from scratch.
    # Otherwise, it is fresh, and a <tt>304 Not Modified</tt> is sent.
    #
    # ==== Options
    #
    # See #fresh_when for supported options.
    #
    # ==== Examples
    #
    #   def show
    #     @article = Article.find(params[:id])
    #
    #     if stale?(etag: @article, last_modified: @article.updated_at)
    #       @statistics = @article.really_expensive_call
    #       respond_to do |format|
    #         # all the supported formats
    #       end
    #     end
    #   end
    #
    # You can also just pass a record:
    #
    #   def show
    #     @article = Article.find(params[:id])
    #
    #     if stale?(@article)
    #       @statistics = @article.really_expensive_call
    #       respond_to do |format|
    #         # all the supported formats
    #       end
    #     end
    #   end
    #
    # +etag+ will be set to the record, and +last_modified+ will be set to the
    # record's +updated_at+.
    #
    # You can also pass an object that responds to +maximum+, such as a
    # collection of records:
    #
    #   def index
    #     @articles = Article.all
    #
    #     if stale?(@articles)
    #       @statistics = @articles.really_expensive_call
    #       respond_to do |format|
    #         # all the supported formats
    #       end
    #     end
    #   end
    #
    # In this case, +etag+ will be set to the collection, and +last_modified+
    # will be set to <tt>maximum(:updated_at)</tt> (the timestamp of the most
    # recently updated record).
    #
    # When passing a record or a collection, you can still specify other
    # options, such as +:public+ and +:cache_control+:
    #
    #   def show
    #     @article = Article.find(params[:id])
    #
    #     if stale?(@article, public: true, cache_control: { no_cache: true })
    #       @statistics = @articles.really_expensive_call
    #       respond_to do |format|
    #         # all the supported formats
    #       end
    #     end
    #   end
    #
    # The above will set <tt>Cache-Control: public, no-cache</tt> in the response.
    #
    # When rendering a different template than the controller/action's default
    # template, you can indicate which digest to include in the ETag:
    #
    #   def show
    #     super if stale?(@article, template: "widgets/show")
    #   end
    #
    def stale?(object = nil, **freshness_kwargs)
      fresh_when(object, **freshness_kwargs)
      !request.fresh?(response)
    end

    # Sets the +Cache-Control+ header, overwriting existing directives. This
    # method will also ensure an HTTP +Date+ header for client compatibility.
    #
    # Defaults to issuing the +private+ directive, so that intermediate caches
    # must not cache the response.
    #
    # ==== Options
    #
    # [+:public+]
    #   If true, replaces the default +private+ directive with the +public+
    #   directive.
    # [+:must_revalidate+]
    #   If true, adds the +must-revalidate+ directive.
    # [+:stale_while_revalidate+]
    #   Sets the value of the +stale-while-revalidate+ directive.
    # [+:stale_if_error+]
    #   Sets the value of the +stale-if-error+ directive.
    #
    # Any additional key-value pairs are concatenated as directives. For a list
    # of supported +Cache-Control+ directives, see the {article on
    # MDN}[https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control].
    #
    # ==== Examples
    #
    #   expires_in 10.minutes
    #   # => Cache-Control: max-age=600, private
    #
    #   expires_in 10.minutes, public: true
    #   # => Cache-Control: max-age=600, public
    #
    #   expires_in 10.minutes, public: true, must_revalidate: true
    #   # => Cache-Control: max-age=600, public, must-revalidate
    #
    #   expires_in 1.hour, stale_while_revalidate: 60.seconds
    #   # => Cache-Control: max-age=3600, private, stale-while-revalidate=60
    #
    #   expires_in 1.hour, stale_if_error: 5.minutes
    #   # => Cache-Control: max-age=3600, private, stale-if-error=300
    #
    #   expires_in 1.hour, public: true, "s-maxage": 3.hours, "no-transform": true
    #   # => Cache-Control: max-age=3600, public, s-maxage=10800, no-transform=true
    #
    def expires_in(seconds, options = {})
      response.cache_control.delete(:no_store)
      response.cache_control.merge!(
        max_age: seconds,
        public: options.delete(:public),
        must_revalidate: options.delete(:must_revalidate),
        stale_while_revalidate: options.delete(:stale_while_revalidate),
        stale_if_error: options.delete(:stale_if_error),
      )
      options.delete(:private)

      response.cache_control[:extras] = options.map { |k, v| "#{k}=#{v}" }
      response.date = Time.now unless response.date?
    end

    # Sets an HTTP 1.1 +Cache-Control+ header of <tt>no-cache</tt>. This means the
    # resource will be marked as stale, so clients must always revalidate.
    # Intermediate/browser caches may still store the asset.
    def expires_now
      response.cache_control.replace(no_cache: true)
    end

    # Cache or yield the block. The cache is supposed to never expire.
    #
    # You can use this method when you have an HTTP response that never changes,
    # and the browser and proxies should cache it indefinitely.
    #
    # * +public+: By default, HTTP responses are private, cached only on the
    #   user's web browser. To allow proxies to cache the response, set +true+ to
    #   indicate that they can serve the cached response to all users.
    def http_cache_forever(public: false)
      expires_in 100.years, public: public

      yield if stale?(etag: request.fullpath,
                      last_modified: Time.new(2011, 1, 1).utc,
                      public: public)
    end

    # Sets an HTTP 1.1 +Cache-Control+ header of <tt>no-store</tt>. This means the
    # resource may not be stored in any cache.
    def no_store
      response.cache_control.replace(no_store: true)
    end

    private
      def combine_etags(validator, options)
        [validator, *etaggers.map { |etagger| instance_exec(options, &etagger) }].compact
      end
  end
end