Storyboards: Cleanup and document code

src/invidious/videos/storyboard.cr

@@ -3,74 +3,110 @@ require "http/params"
 
 module Invidious::Videos
   struct Storyboard
-    getter url : String
+    # Template URL
+    getter url : URI
+    getter proxied_url : URI
+
+    # Thumbnail parameters
     getter width : Int32
     getter height : Int32
     getter count : Int32
     getter interval : Int32
-    getter storyboard_width : Int32
-    getter storyboard_height : Int32
-    getter storyboard_count : Int32
+
+    # Image (storyboard) parameters
+    getter rows : Int32
+    getter columns : Int32
+    getter images_count : Int32
 
     def initialize(
       *, @url, @width, @height, @count, @interval,
-      @storyboard_width, @storyboard_height, @storyboard_count
+      @rows, @columns, @images_count
     )
+      authority = /(i\d?).ytimg.com/.match(@url.host.not_nil!).not_nil![1]?
+
+      @proxied_url = URI.parse(HOST_URL)
+      @proxied_url.path = "/sb/#{authority}#{@url.path}"
+      @proxied_url.query = @url.query
     end
 
     # Parse the JSON structure from Youtube
-    def self.from_yt_json(container : JSON::Any)
+    def self.from_yt_json(container : JSON::Any) : Array(Storyboard)
+      # Livestream storyboards are a bit different
+      # TODO: document exactly how
+      if storyboard = container.dig?("playerLiveStoryboardSpecRenderer", "spec").try &.as_s
+        return [Storyboard.new(
+          url: URI.parse(storyboard.split("#")[0]),
+          width: 106,
+          height: 60,
+          count: -1,
+          interval: 5000,
+          rows: 3,
+          columns: 3,
+          images_count: -1
+        )]
+      end
+
+      # Split the storyboard string into chunks
+      #
+      # General format (whitespaces added for legibility):
+      #   https://i.ytimg.com/sb/<video_id>/storyboard3_L$L/$N.jpg?sqp=<sig0>
+      #   |  48 #  27 #  100 #  10 #  10 #      0 #  default #  rs$<sig1>
+      #   |  80 #  45 #   95 #  10 #  10 #  10000 #      M$M #  rs$<sig2>
+      #   | 160 #  90 #   95 #   5 #   5 #  10000 #      M$M #  rs$<sig3>
+      #
       storyboards = container.dig?("playerStoryboardSpecRenderer", "spec")
         .try &.as_s.split("|")
 
-      if !storyboards
-        if storyboard = container.dig?("playerLiveStoryboardSpecRenderer", "spec").try &.as_s
-          return [Storyboard.new(
-            url: storyboard.split("#")[0],
-            width: 106,
-            height: 60,
-            count: -1,
-            interval: 5000,
-            storyboard_width: 3,
-            storyboard_height: 3,
-            storyboard_count: -1,
-          )]
-        end
-      end
-
-      items = [] of Storyboard
-
-      return items if !storyboards
+      return [] of Storyboard if !storyboards
 
+      # The base URL is the first chunk
       url = URI.parse(storyboards.shift)
-      params = HTTP::Params.parse(url.query || "")
+      params = url.query_params
 
-      storyboards.each_with_index do |sb, i|
-        width, height, count, storyboard_width, storyboard_height, interval, _, sigh = sb.split("#")
-        params["sigh"] = sigh
-        url.query = params.to_s
+      return storyboards.map_with_index do |sb, i|
+        # Separate the different storyboard parameters:
+        # width/height: respective dimensions, in pixels, of a single thumbnail
+        # count: how many thumbnails are displayed across the full video
+        # columns/rows: maximum amount of thumbnails that can be stuffed in a
+        #   single image, horizontally and vertically.
+        # interval: interval between two thumbnails, in milliseconds
+        # sigh: URL cryptographic signature
+        width, height, count, columns, rows, interval, _, sigh = sb.split("#")
 
         width = width.to_i
         height = height.to_i
         count = count.to_i
         interval = interval.to_i
-        storyboard_width = storyboard_width.to_i
-        storyboard_height = storyboard_height.to_i
-        storyboard_count = (count / (storyboard_width * storyboard_height)).ceil.to_i
+        columns = columns.to_i
+        rows = rows.to_i
 
-        items << Storyboard.new(
-          url: url.to_s.sub("$L", i).sub("$N", "M$M"),
+        # Add the signature to the URL
+        params["sigh"] = sigh
+        url.query = params.to_s
+
+        # Replace the template parts with what we have
+        url.path = url.path.sub("$L", i).sub("$N", "M$M")
+
+        # This value represents the maximum amount of thumbnails that can fit
+        # in a single image. The last image (or the only one for short videos)
+        # will contain less thumbnails than that.
+        thumbnails_per_image = columns * rows
+
+        # This value represents the total amount of storyboards required to
+        # hold all of the thumbnails. It can't be less than 1.
+        images_count = (count / thumbnails_per_image).ceil.to_i
+
+        Storyboard.new(
+          url: url,
           width: width,
           height: height,
           count: count,
           interval: interval,
-          storyboard_width: storyboard_width,
-          storyboard_height: storyboard_height,
-          storyboard_count: storyboard_count
+          rows: rows,
+          columns: columns,
+          images_count: images_count,
         )
       end
-
-      items
     end
   end
 end