[Enhancement] Capture playlist_index for use with output templates (#315)

* Started capturing playlist_index on indexing pass

* Added playlist_index as a media item field

* Added playlist index to output variable templates

* Improved the way playlist_indexes are rejected on update

* Updated docs

* Undid unneeded changes

lib/pinchflat/downloading/download_option_builder.ex

@@ -203,6 +203,7 @@ defmodule Pinchflat.Downloading.DownloadOptionBuilder do
       "source_collection_id" => source.collection_id,
       "source_collection_name" => source.collection_name,
       "source_collection_type" => to_string(source.collection_type),
+      "media_playlist_index" => to_string(media_item_with_preloads.playlist_index),
       "media_upload_date_index" =>
         media_item_with_preloads.upload_date_index
         |> to_string()

lib/pinchflat/media/media.ex

@@ -142,12 +142,17 @@ defmodule Pinchflat.Media do
   """
   def create_media_item_from_backend_attrs(source, media_attrs_struct) do
     attrs = Map.merge(%{source_id: source.id}, Map.from_struct(media_attrs_struct))
+    # Some fields should only be set on insert and not on update.
+    fields_to_drop_on_update = [:playlist_index]
 
     %MediaItem{}
     |> MediaItem.changeset(attrs)
     |> Repo.insert(
       on_conflict: [
-        set: Map.to_list(attrs)
+        set:
+          attrs
+          |> Map.drop(fields_to_drop_on_update)
+          |> Map.to_list()
       ],
       conflict_target: [:source_id, :media_id]
     )

lib/pinchflat/media/media_item.ex

@@ -18,6 +18,8 @@ defmodule Pinchflat.Media.MediaItem do
   alias Pinchflat.Media.MediaItemsSearchIndex
 
   @allowed_fields [
+    # these fields are only captured on index
+    :playlist_index,
     # these fields are captured on indexing (and again on download)
     :title,
     :media_id,
@@ -72,6 +74,7 @@ defmodule Pinchflat.Media.MediaItem do
     field :uploaded_at, :utc_datetime
     field :upload_date_index, :integer, default: 0
     field :duration_seconds, :integer
+    field :playlist_index, :integer, default: 0
 
     field :media_filepath, :string
     field :media_size_bytes, :integer

lib/pinchflat/yt_dlp/media.ex

@@ -22,7 +22,8 @@ defmodule Pinchflat.YtDlp.Media do
     :livestream,
     :short_form_content,
     :uploaded_at,
-    :duration_seconds
+    :duration_seconds,
+    :playlist_index
   ]
 
   alias __MODULE__
@@ -63,7 +64,7 @@ defmodule Pinchflat.YtDlp.Media do
   @doc """
   Returns a map representing the media at the given URL.
 
-  Returns {:ok, [map()]} | {:error, any, ...}.
+  Returns {:ok, %Media{}} | {:error, any, ...}.
   """
   def get_media_attributes(url) do
     runner = Application.get_env(:pinchflat, :yt_dlp_runner)
@@ -84,9 +85,11 @@ defmodule Pinchflat.YtDlp.Media do
 
   @doc """
   Returns the output template for yt-dlp's indexing command.
+
+  NOTE: playlist_index is really only useful for playlists that will never change their order.
   """
   def indexing_output_template do
-    "%(.{id,title,was_live,webpage_url,description,aspect_ratio,duration,upload_date,timestamp})j"
+    "%(.{id,title,was_live,webpage_url,description,aspect_ratio,duration,upload_date,timestamp,playlist_index})j"
   end
 
   @doc """
@@ -104,7 +107,8 @@ defmodule Pinchflat.YtDlp.Media do
       livestream: !!response["was_live"],
       duration_seconds: response["duration"] && round(response["duration"]),
       short_form_content: response["webpage_url"] && short_form_content?(response),
-      uploaded_at: response["upload_date"] && parse_uploaded_at(response)
+      uploaded_at: response["upload_date"] && parse_uploaded_at(response),
+      playlist_index: response["playlist_index"] || 0
     }
   end