Parse hashtag header when getting the first hashtag page

src/invidious/hashtag.cr

@@ -1,15 +1,42 @@
 module Invidious::Hashtag
   extend self
 
-  def fetch(hashtag : String, page : Int, region : String? = nil) : Array(SearchItem)
+  def fetch(hashtag : String, page : Int, region : String? = nil) : HashtagPage
     cursor = (page - 1) * 60
-    ctoken = generate_continuation(hashtag, cursor)
-
+    header = nil
     client_config = YoutubeAPI::ClientConfig.new(region: region)
-    response = YoutubeAPI.browse(continuation: ctoken, client_config: client_config)
+    # for any page besides the first page, get the list of videos
+    if cursor > 0
+      ctoken = generate_continuation(hashtag, cursor)
+      response = YoutubeAPI.browse(continuation: ctoken, client_config: client_config)
+    else
+      # get first page + header info
+      response = YoutubeAPI.browse("FEhashtag", params: get_hashtag_first_page(hashtag), client_config: client_config)
+      if header = response.dig?("header")
+        header = parse_item(header).as(HashtagHeader)
+      end
+    end
 
     items, _ = extract_items(response)
-    return items
+    return HashtagPage.new({
+      videos: items,
+      header: header,
+    })
+  end
+
+  def get_hashtag_first_page(hashtag : String)
+    object = {
+      "93:embedded" => {
+        "1:string" => hashtag,
+        "2:varint" => 0_i64,
+        "3:varint" => 1_i64,
+      },
+    }
+
+    return object.try { |i| Protodec::Any.cast_json(i) }
+      .try { |i| Protodec::Any.from_json(i) }
+      .try { |i| Base64.urlsafe_encode(i) }
+      .try { |i| URI.encode_www_form(i) }
   end
 
   def generate_continuation(hashtag : String, cursor : Int)

src/invidious/helpers/serialized_yt_data.cr

@@ -274,4 +274,63 @@ struct Continuation
   end
 end
 
+struct HashtagPage
+  include DB::Serializable
+
+  property videos : Array(SearchItem) | Array(Video)
+  property header : HashtagHeader?
+
+  def to_json(locale : String?, json : JSON::Builder)
+    json.object do
+      json.field "type", "hashtag"
+      if self.header != nil
+        json.field "header" do
+          self.header.to_json(json)
+        end
+      end
+      json.field "results" do
+        json.array do
+          self.videos.each do |item|
+            item.to_json(locale, json)
+          end
+        end
+      end
+    end
+  end
+
+  # TODO: remove the locale and follow the crystal convention
+  def to_json(locale : String?, _json : Nil)
+    JSON.build do |json|
+      to_json(locale, json)
+    end
+  end
+
+  def to_json(json : JSON::Builder)
+    to_json(nil, json)
+  end
+end
+
+struct HashtagHeader
+  include DB::Serializable
+
+  property tag : String
+  property channel_count : Int64
+  property video_count : Int64
+
+  def to_json(json : JSON::Builder)
+    json.object do
+      json.field "type", "hashtagHeader"
+      json.field "hashtag", self.tag
+      json.field "channelCount", self.channel_count
+      json.field "videoCount", self.video_count
+    end
+  end
+
+  def to_json(_json : Nil)
+    JSON.build do |json|
+      to_json(json)
+    end
+  end
+end
+
 alias SearchItem = SearchVideo | SearchChannel | SearchPlaylist | Category

src/invidious/routes/api/v1/search.cr

@@ -66,21 +66,13 @@ module Invidious::Routes::API::V1::Search
     env.response.content_type = "application/json"
 
     begin
-      results = Invidious::Hashtag.fetch(hashtag, page, region)
+      hashtagPage = Invidious::Hashtag.fetch(hashtag, page, region)
     rescue ex
       return error_json(400, ex)
     end
 
     JSON.build do |json|
-      json.object do
-        json.field "results" do
-          json.array do
-            results.each do |item|
-              item.to_json(locale, json)
-            end
-          end
-        end
-      end
+      hashtagPage.to_json(locale, json)
     end
   end
 end

src/invidious/routes/search.cr

@@ -91,7 +91,8 @@ module Invidious::Routes::Search
     end
 
     begin
-      videos = Invidious::Hashtag.fetch(hashtag, page)
+      hashtagPage = Invidious::Hashtag.fetch(hashtag, page)
+      videos = hashtagPage.videos
     rescue ex
       return error_template(500, ex)
     end

src/invidious/yt_backend/extractors.cr

@@ -20,6 +20,7 @@ private ITEM_PARSERS = {
   Parsers::ReelItemRendererParser,
   Parsers::ItemSectionRendererParser,
   Parsers::ContinuationItemRendererParser,
+  Parsers::HashtagHeaderRenderer,
 }
 
 private alias InitialData = Hash(String, JSON::Any)
@@ -550,6 +551,39 @@ private module Parsers
       return {{@type.name}}
     end
   end
+
+  # Parses an InnerTube hashtagHeaderRender into a HashtagHeaderRender.
+  # Returns nil when the given object isn't a hashtagHeaderRender.
+  #
+  # hashtagHeaderRender contains metadate of the hashtag page such as video count and channel count
+  #
+  module HashtagHeaderRenderer
+    def self.process(item : JSON::Any, author_fallback : AuthorFallback)
+      if item_contents = item["hashtagHeaderRenderer"]?
+        return self.parse(item_contents)
+      end
+    end
+
+    private def self.parse(item_contents)
+      info = extract_text(item_contents.dig?("hashtagInfoText")) || ""
+
+      regex_match = /(?<videos>\d+\S)\D+(?<channels>\d+\S)/.match(info)
+
+      hashtag = extract_text(item_contents.dig?("hashtag")) || ""
+      videos = short_text_to_number(regex_match.try &.["videos"]?.try &.to_s || "0")
+      channels = short_text_to_number(regex_match.try &.["channels"]?.try &.to_s || "0")
+
+      return HashtagHeader.new({
+        tag:           hashtag,
+        channel_count: channels,
+        video_count:   videos,
+      })
+    end
+
+    def self.parser_name
+      return {{@type.name}}
+    end
+  end
 end
 
 # The following are the extractors for extracting an array of items from