Parse hashtag header when getting the first hashtag page

src/invidious/hashtag.cr

@@ -1,18 +1,99 @@
 module Invidious::Hashtag
   extend self
 
-  def fetch(hashtag : String, page : Int, region : String? = nil) : Array(SearchItem)
+  struct HashtagPage
+    include DB::Serializable
+
+    property videos : Array(SearchItem) | Array(Video)
+    property header : HashtagHeader?
+    property has_next_continuation : Bool
+
+    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
+        json.field "hasNextPage", self.has_next_continuation
+      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 "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
+
+  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)
+    item = generate_continuation(hashtag, cursor)
+    # item is a ctoken
+    if cursor > 0
+      response = YoutubeAPI.browse(continuation: item, client_config: client_config)
+    else
+      # item browses the first page (including metadata)
+      response = YoutubeAPI.browse("FEhashtag", params: item, client_config: client_config)
+      if item_contents = response.dig?("header", "hashtagHeaderRenderer")
+        header = parse_hashtag_renderer(item_contents)
+      end
+    end
 
-    items, _ = extract_items(response)
+    items, next_continuation = extract_items(response)
-    return items
+    return HashtagPage.new({
+      videos:                items,
+      header:                header,
+      has_next_continuation: next_continuation != nil,
+    })
   end
 
   def generate_continuation(hashtag : String, cursor : Int)
+    object = {
+      "93:2:embedded" => {
+        "1:string" => hashtag,
+        "2:varint" => 0_i64,
+        "3:varint" => 1_i64,
+      },
+    }
+    if cursor > 0
       object = {
         "80226972:embedded" => {
           "2:string" => "FEhashtag",
@@ -31,12 +112,27 @@ module Invidious::Hashtag
           "35:string" => "browse-feedFEhashtag",
         },
       }
+    end
 
-    continuation = object.try { |i| Protodec::Any.cast_json(i) }
+    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
 
-    return continuation
+  def parse_hashtag_renderer(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
 end

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

@@ -69,21 +69,13 @@ 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
+      hashtagPage.to_json(locale, json)
-        json.field "results" do
-          json.array do
-            results.each do |item|
-              item.to_json(locale, json)
-            end
-          end
-        end
-      end
     end
   end
 end

src/invidious/routes/search.cr

@@ -101,7 +101,8 @@ module Invidious::Routes::Search
     end
 
     begin
-      items = Invidious::Hashtag.fetch(hashtag, page)
+      hashtagPage = Invidious::Hashtag.fetch(hashtag, page)
+      items = hashtagPage.videos
     rescue ex
       return error_template(500, ex)
     end