Support OpenGraph video embeds (#4897)

* Support OpenGraph video embeds

It's not really OpenGraph, it's twitter:player property, but it's
not OEmbed so that fits. For example, this allows Twitch clips to
be displayed as embeds.

Also, fixes glitch-soc/mastodon#135

* Fix invalid OpenGraph cards being saved through attaching and
revisit URLs after 14 days

app/services/fetch_link_card_service.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class FetchLinkCardService < BaseService
+  include ActionView::Helpers::TagHelper
+
   URL_PATTERN = %r{https?://\S+}
 
   def call(status)
@@ -14,11 +16,11 @@ class FetchLinkCardService < BaseService
     RedisLock.acquire(lock_options) do |lock|
       if lock.acquired?
         @card = PreviewCard.find_by(url: @url)
-        process_url if @card.nil?
+        process_url if @card.nil? || @card.updated_at <= 2.weeks.ago
       end
     end
 
-    attach_card unless @card.nil?
+    attach_card if @card&.persisted?
   rescue HTTP::ConnectionError, OpenSSL::SSL::SSLError
     nil
   end
@@ -26,7 +28,7 @@ class FetchLinkCardService < BaseService
   private
 
   def process_url
-    @card = PreviewCard.new(url: @url)
+    @card ||= PreviewCard.new(url: @url)
     res     = Request.new(:head, @url).perform
 
     return if res.code != 200 || res.mime_type != 'text/html'
@@ -106,12 +108,25 @@ class FetchLinkCardService < BaseService
     guess = detector.detect(html, response.charset)
     page  = Nokogiri::HTML(html, nil, guess&.fetch(:encoding))
 
+    if meta_property(page, 'twitter:player')
+      @card.type   = :video
+      @card.width  = meta_property(page, 'twitter:player:width') || 0
+      @card.height = meta_property(page, 'twitter:player:height') || 0
+      @card.html   = content_tag(:iframe, nil, src: meta_property(page, 'twitter:player'),
+                                               width: @card.width,
+                                               height: @card.height,
+                                               allowtransparency: 'true',
+                                               scrolling: 'no',
+                                               frameborder: '0')
+    else
       @card.type             = :link
-    @card.title            = meta_property(page, 'og:title') || page.at_xpath('//title')&.content || ''
-    @card.description      = meta_property(page, 'og:description') || meta_property(page, 'description') || ''
       @card.image_remote_url = meta_property(page, 'og:image') if meta_property(page, 'og:image')
+    end
 
-    return if @card.title.blank?
+    @card.title            = meta_property(page, 'og:title').presence || page.at_xpath('//title')&.content || ''
+    @card.description      = meta_property(page, 'og:description').presence || meta_property(page, 'description') || ''
+
+    return if @card.title.blank? && @card.html.blank?
 
     @card.save_with_optional_image!
   end