Add subscription JSON export for NewPipe (#5826)

The current option to export subscriptions for NewPipe (`Export subscriptions as OPML (for NewPipe & FreeTube)`) isn't accepted by NewPipe anymore. As far as I can tell, NewPipe only accepts importing from its own SQLite database, from Google Account CSV export and from its own JSON export format. This is mentioned in https://github.com/iv-org/invidious/issues/5438.

This PR adds support to export subscriptions in the NewPipe compatible format. I'm looking for input on a few points:
- I'm not a huge fan of hardcoding the NewPipe version in the export, but it is required by NewPipe to recognize it as a valid file. If someone has a better idea I'm all ears but I think it's the only way. In any case, NewPipe can import formats in a backwards compatible way in the future so it shouldn't be a huge deal.
- I haven't checked if the OPML export option actually works for FreeTube. If it doesn't, it should probably be removed altogether, for now I just removed the `(for NewPipe)` part.
- The translations would need to be updated, but I don't know how that is handled in this project so I need some help there.

The new format looks like this:
```
{
  "subscriptions": [
    {
      "service_id": 0,
      "url": "https://www.youtube.com/channel/UCHnyfMqiRRG1u-2MsSQLbXA",
      "name": "Veritasium"
    },
    {
      "service_id": 0,
      "url": "https://www.youtube.com/channel/UC6nSFpj9HTCZ5t-N3Rm3-HA",
      "name": "Vsauce"
    }
  ],
  "app_version": "0.29.0",
  "app_version_int": 1014
}
```


* add subscription json export for NewPipe

* remove old newpipe export format

* make newpipe export values constant

* remove duplicate export option, add i18n keys

* Convert to_newpipe to a serializable struct

* Use same naming format as NewPipe for the exported subscriptions

---------

Co-authored-by: Fijxu <fijxu@nadeko.net>

locales/en-US.json

@@ -51,8 +51,8 @@
     "Import NewPipe subscriptions (.json)": "Import NewPipe subscriptions (.json)",
     "Import NewPipe data (.zip)": "Import NewPipe data (.zip)",
     "Export": "Export",
-    "Export subscriptions as OPML": "Export subscriptions as OPML",
-    "Export subscriptions as OPML (for NewPipe & FreeTube)": "Export subscriptions as OPML (for NewPipe & FreeTube)",
+    "Export subscriptions as OPML (for FreeTube)": "Export subscriptions as OPML (for FreeTube)",
+    "Export subscriptions as JSON (for NewPipe)": "Export subscriptions as JSON (for NewPipe)",
     "Export data as JSON": "Export Invidious data as JSON",
     "Delete account?": "Delete account?",
     "History": "History",

src/invidious/routes/subscriptions.cr

@@ -80,30 +80,28 @@ module Invidious::Routes::Subscriptions
     subscriptions.sort_by!(&.author.downcase)
 
     if action_takeout
-      if format == "json"
-        env.response.content_type = "application/json"
-        env.response.headers["content-disposition"] = "attachment"
+      env.response.content_type = "application/json"
 
+      # Exports the NewPipe with the same naming format NewPipe
+      # uses for their exports
+      # Exmaple: `newpipe_subscriptions_202610312013`
+      export_time = Time.local.to_s("%Y%m%d%H%M")
+      env.response.headers["Content-Disposition"] = "attachment; filename=\"newpipe_subscriptions_#{export_time}\""
+
+      if format == "json"
         return Invidious::User::Export.to_invidious(user)
+      elsif format == "newpipe_json"
+        return Invidious::User::Export.to_newpipe(subscriptions)
       else
         env.response.content_type = "application/xml"
-        env.response.headers["content-disposition"] = "attachment"
         export = XML.build do |xml|
           xml.element("opml", version: "1.1") do
             xml.element("body") do
-              if format == "newpipe"
-                title = "YouTube Subscriptions"
-              else
-                title = "Invidious Subscriptions"
-              end
+              title = "Invidious Subscriptions"
 
               xml.element("outline", text: title, title: title) do
                 subscriptions.each do |channel|
-                  if format == "newpipe"
-                    xml_url = "https://www.youtube.com/feeds/videos.xml?channel_id=#{channel.id}"
-                  else
-                    xml_url = "#{HOST_URL}/feed/channel/#{channel.id}"
-                  end
+                  xml_url = "#{HOST_URL}/feed/channel/#{channel.id}"
 
                   xml.element("outline", text: channel.author, title: channel.author,
                     "type": "rss", xmlUrl: xml_url)

src/invidious/user/exports.cr

@@ -2,6 +2,42 @@ struct Invidious::User
   module Export
     extend self
 
+    struct NewPipe
+      include JSON::Serializable
+
+      # Hardcoded NewPipe values that are needed
+      # so NewPipe can import the JSON.
+      private APP_VERSION     = "0.29.0"
+      private APP_VERSION_INT = 1014
+      private YT_SERVICE_ID   =    0
+
+      getter subscriptions : Array(Subscription)
+
+      struct Subscription
+        include JSON::Serializable
+
+        getter service_id : Int32 = YT_SERVICE_ID
+        getter url : String
+        getter name : String
+
+        def initialize(channel : InvidiousChannel)
+          @url = "https://www.youtube.com/channel/" + channel.id
+          @name = channel.author
+        end
+      end
+
+      getter app_version : String = APP_VERSION
+      getter app_version_int : Int32 = APP_VERSION_INT
+
+      def initialize(channels : Array(InvidiousChannel))
+        @subscriptions = channels.map { |channel| Subscription.new(channel) }
+      end
+    end
+
+    def to_newpipe(subscriptions : Array(InvidiousChannel))
+      NewPipe.new(subscriptions).to_json
+    end
+
     def to_invidious(user : User)
       playlists = Invidious::Database::Playlists.select_like_iv(user.email)
 

src/invidious/views/user/data_control.ecr

@@ -53,11 +53,11 @@
             <legend><%= I18n.translate(locale, "Export") %></legend>
 
             <div class="pure-control-group">
-                <a href="/subscription_manager?action_takeout=1"><%= I18n.translate(locale, "Export subscriptions as OPML") %></a>
+                <a href="/subscription_manager?action_takeout=1&format=opml"><%= I18n.translate(locale, "Export subscriptions as OPML (for FreeTube)") %></a>
             </div>
 
             <div class="pure-control-group">
-                <a href="/subscription_manager?action_takeout=1&format=newpipe"><%= I18n.translate(locale, "Export subscriptions as OPML (for NewPipe & FreeTube)") %></a>
+                <a href="/subscription_manager?action_takeout=1&format=newpipe_json"><%= I18n.translate(locale, "Export subscriptions as JSON (for NewPipe)") %></a>
             </div>
 
             <div class="pure-control-group">