card: add the airing mode, a date-bounded discovery row

TMDB knows what airs today; asking the indexers instead would mean one query
per show per day, which is the load that wedges a Prowlarr. So the row is
bounded by air date: TV to the single day, film to a fortnight (a day of
cinema releases is usually empty). The vote floor is lifted on this row only —
a season airing now has not collected 50 votes yet, and the shared floor would
empty exactly the row it is meant to fill. The bound is computed per request,
so the row rolls over at midnight with nothing scheduled.

feeder-plugin/card-feeder/src/discovery.rs

@@ -77,6 +77,15 @@ pub(crate) enum DiscoveryMode {
     Popular,
     Trending,
     TopRated,
+    /// What came out **today** — the day-by-day row. TV: shows with an episode
+    /// airing today; film: releases from the last fortnight.
+    ///
+    /// Date-bounded rather than availability-bounded on purpose. "Is a file out
+    /// yet" is an indexer question, and asking it per show per day is exactly
+    /// the load that wedges a Prowlarr; an air date is a fact TMDB already
+    /// holds, costs the same single call as every other row, and makes the row
+    /// roll over by itself at midnight with nothing scheduled.
+    Airing,
 }
 
 impl DiscoveryMode {
@@ -94,6 +103,7 @@ impl DiscoveryMode {
             DiscoveryMode::Popular => "popular",
             DiscoveryMode::Trending => "trending",
             DiscoveryMode::TopRated => "top_rated",
+            DiscoveryMode::Airing => "airing",
         }
     }
 
@@ -103,7 +113,11 @@ impl DiscoveryMode {
     fn discover_sort(self) -> &'static str {
         match self {
             DiscoveryMode::TopRated => "vote_average.desc",
-            DiscoveryMode::Popular | DiscoveryMode::Trending => "popularity.desc",
+            // Airing sorts by popularity too: the date bound is what selects the
+            // row, so the sort only decides who leads it.
+            DiscoveryMode::Popular | DiscoveryMode::Trending | DiscoveryMode::Airing => {
+                "popularity.desc"
+            }
         }
     }
 }
@@ -124,6 +138,10 @@ pub(crate) fn is_discovery_query(query: &GatewayQuery) -> bool {
 /// First truthy mode marker on the query, in precedence order.
 fn discovery_mode(query: &GatewayQuery) -> Option<DiscoveryMode> {
     for mode in [
+        // Airing leads: it is the most specific claim a row can make, and a
+        // caller that sends `airing:true popular:true` means "today's, by
+        // popularity", not "popular, ever".
+        DiscoveryMode::Airing,
         DiscoveryMode::Trending,
         DiscoveryMode::Popular,
         DiscoveryMode::TopRated,
@@ -203,6 +221,63 @@ fn with_genres_ids(wanted: &[String], names: &HashMap<u32, String>) -> Vec<u32>
     ids
 }
 
+/// How far back the film side of [`DiscoveryMode::Airing`] reaches, in days.
+///
+/// A series airs an episode on a given day, so "today" is a real set. Films do
+/// not: a single day's releases are usually empty, and a viewer opening the app
+/// on a Tuesday still means "what's new". A fortnight is the smallest window
+/// that keeps the row populated without turning it into "this year".
+const AIRING_MOVIE_WINDOW_DAYS: i64 = 13;
+
+/// Today, UTC, as `YYYY-MM-DD` — the bound [`DiscoveryMode::Airing`] is built
+/// from. UTC rather than a local zone: the feeder serves peers in every zone,
+/// and TMDB's air dates are themselves zone-less calendar dates.
+fn today_utc_days() -> i64 {
+    std::time::SystemTime::now()
+        .duration_since(std::time::UNIX_EPOCH)
+        .map(|d| (d.as_secs() / 86_400) as i64)
+        .unwrap_or(0)
+}
+
+/// `YYYY-MM-DD` for a count of days since 1970-01-01.
+///
+/// Hand-rolled (Howard Hinnant's civil-from-days) rather than pulling in a date
+/// crate for one format call — and split from [`today_utc_days`] so the whole
+/// thing is testable against known dates instead of "whatever today is".
+fn fmt_days(days: i64) -> String {
+    let z = days + 719_468;
+    let era = if z >= 0 { z } else { z - 146_096 } / 146_097;
+    let doe = (z - era * 146_097) as i64; // [0, 146096]
+    let yoe = (doe - doe / 1460 + doe / 36_524 - doe / 146_096) / 365; // [0, 399]
+    let y = yoe + era * 400;
+    let doy = doe - (365 * yoe + yoe / 4 - yoe / 100); // [0, 365]
+    let mp = (5 * doy + 2) / 153; // [0, 11]
+    let d = doy - (153 * mp + 2) / 5 + 1; // [1, 31]
+    let m = if mp < 10 { mp + 3 } else { mp - 9 }; // [1, 12]
+    let y = if m <= 2 { y + 1 } else { y };
+    format!("{y:04}-{m:02}-{d:02}")
+}
+
+/// The `/discover` date bounds for [`DiscoveryMode::Airing`], given today.
+///
+/// TV bounds `air_date` to the single day, which is what makes the row
+/// "today's episodes" and what makes it roll over on its own. Film bounds
+/// `primary_release_date` to [`AIRING_MOVIE_WINDOW_DAYS`] back — see that
+/// constant for why the two kinds cannot share a window.
+fn airing_bounds(kind: TmdbKind, today: i64) -> String {
+    match kind {
+        TmdbKind::Tv => {
+            let d = fmt_days(today);
+            format!("air_date.gte={d}&air_date.lte={d}&")
+        }
+        TmdbKind::Movie => format!(
+            "primary_release_date.gte={}&primary_release_date.lte={}&",
+            fmt_days(today - AIRING_MOVIE_WINDOW_DAYS),
+            fmt_days(today),
+        ),
+    }
+}
+
 /// Build the `path_and_query` for `TmdbClient::discovery_list` from the mode,
 /// kind, anime flag, requested genre ids, and 1-based `page`.
 fn build_path_and_query(
@@ -244,8 +319,18 @@ fn build_path_and_query(
     // single 10.0 vote on top, which a 50-vote gate doesn't stop.
     let votes = match mode {
         DiscoveryMode::TopRated => 200,
+        // ⚠ No vote floor on the airing row, and that is the point. The shared
+        // gate exists to keep unrated residue off a popularity ranking; here the
+        // date bound already decides membership, and a floor would filter out
+        // exactly what the row is for — a series whose first season is airing
+        // now has not had time to collect 50 votes.
+        DiscoveryMode::Airing => 0,
         _ => DISCOVERY_MIN_VOTES,
     };
+    let dates = match mode {
+        DiscoveryMode::Airing => airing_bounds(kind, today_utc_days()),
+        _ => String::new(),
+    };
     let keyword = if anime {
         format!("with_keywords={TMDB_ANIME_KEYWORD}&")
     } else {
@@ -266,7 +351,7 @@ fn build_path_and_query(
         format!("with_genres={joined}&")
     };
     format!(
-        "discover/{seg}?{keyword}{genres}sort_by={}&include_adult=false\
+        "discover/{seg}?{keyword}{genres}{dates}sort_by={}&include_adult=false\
          &without_keywords={DISCOVERY_EXCLUDED_KEYWORDS}&vote_count.gte={votes}&page={page}",
         mode.discover_sort(),
     )
@@ -719,4 +804,48 @@ mod tests {
         let movie = card_from_hit(&hit(), TmdbKind::Movie, &genre_table());
         assert_eq!(movie.content_kind(), "movie");
     }
+
+    /// The day-by-day row: what selects it, and what it asks TMDB for.
+    ///
+    /// Bounding by air date rather than by availability is the whole design —
+    /// see [`DiscoveryMode::Airing`]. These pin the three parts that make the
+    /// row roll over on its own: the date maths, the bounds per kind, and the
+    /// fact that the vote floor is lifted (a season airing now has no votes
+    /// yet, and the shared floor would empty the row it is meant to fill).
+    #[test]
+    fn airing_row_is_bounded_by_date_not_by_votes() {
+        // Date maths, against known days-since-epoch.
+        assert_eq!(fmt_days(0), "1970-01-01");
+        assert_eq!(fmt_days(19_723), "2024-01-01"); // a leap year's first day
+        assert_eq!(fmt_days(19_782), "2024-02-29"); // the leap day itself
+        assert_eq!(fmt_days(20_453), "2025-12-31");
+
+        // TV: exactly one day, so "today's episodes" is literal.
+        let tv = airing_bounds(TmdbKind::Tv, 19_723);
+        assert_eq!(tv, "air_date.gte=2024-01-01&air_date.lte=2024-01-01&");
+
+        // Film: a fortnight back, because a single day of releases is empty.
+        let movie = airing_bounds(TmdbKind::Movie, 19_723);
+        assert!(movie.contains("primary_release_date.gte=2023-12-19"), "{movie}");
+        assert!(movie.contains("primary_release_date.lte=2024-01-01"), "{movie}");
+
+        // The marker selects the mode, and outranks a co-sent `popular`.
+        assert_eq!(
+            discovery_mode(&query(&[("airing", "true"), ("popular", "true")])),
+            Some(DiscoveryMode::Airing)
+        );
+
+        // The built query carries the date bound and lifts the vote floor.
+        let url = build_path_and_query(DiscoveryMode::Airing, TmdbKind::Tv, false, &[], 1);
+        assert!(url.starts_with("discover/tv?"), "{url}");
+        assert!(url.contains("air_date.gte="), "{url}");
+        assert!(url.contains("vote_count.gte=0"), "{url}");
+        // Still gated for adult residue like every other /discover row.
+        assert!(url.contains("without_keywords="), "{url}");
+
+        // A popular row is unchanged: no date bound, floor intact.
+        let pop = build_path_and_query(DiscoveryMode::Popular, TmdbKind::Tv, false, &[], 1);
+        assert!(!pop.contains("air_date."), "{pop}");
+        assert!(pop.contains(&format!("vote_count.gte={DISCOVERY_MIN_VOTES}")), "{pop}");
+    }
 }