Search and filters

Search is a ListExtractor whose handler is a SearchQueryHandler. Filters, the content types and sort orders a service offers, are a small declarative model in search/filter.

The model

• FilterItem: one selectable option, (int identifier, String name). The identifier is assigned by the builder and is what the rest of the code passes around, not the display name.
• FilterGroup: a named set of FilterItems, with onlyOneCheckable (radio vs checkbox) and its own identifier.
• Filter: a set of FilterGroups, assembled with Filter.Builder.
• SearchFiltersBase: the per-service base. A service subclasses it, creates its items and groups in init(), and implements evaluateSelectedFilters(query) to turn the user's selection into the service's actual request parameters.

A concrete set

YoutubeFilters declares content filters, all, videos, channels, playlists, movies, Lives, plus the YouTube Music ones (music_songs, music_videos, music_albums, music_playlists, music_artists). Its sort and feature groups: sort by (relevance / rating / views), upload date (hour / day / week / month / year), duration (short / long), and feature toggles (HD, subtitles, Creative Commons, 3D, live, 4K, 360, HDR, ...).

evaluateSelectedFilters encodes the selection into YouTube's base64 protobuf sp parameter, which it appends to the search request. Each filter family knows how to serialise itself, so adding one is local.

How a handler exposes them

A ListLinkHandlerFactory advertises getAvailableContentFilter() and getAvailableSortFilter(). The app reads those to build its filter UI, then passes the chosen FilterItems back through fromQuery(query, contentFilters, sortFilters). The selected filters land on the SearchQueryHandler that the SearchExtractor receives, and from there on the request.