// Playlist as an ordered list of Track records. Demonstrates building,
// reordering, and summarizing a list of records, plus sort_by/pluck over
// record fields and total-duration aggregation.

cell Playlist {
    face {
        signal tracks() -> List
        signal total_seconds() -> Int
        signal by_artist(artist: String) -> List
        signal longest() -> Map
        signal titles_sorted() -> List
    }

    on tracks() {
        return list(
            Track { title: "Aurora",  artist: "Nim",  secs: 210 },
            Track { title: "Boreal",  artist: "Nim",  secs: 185 },
            Track { title: "Cinder",  artist: "Vox",  secs: 240 },
            Track { title: "Dune",    artist: "Vox",  secs: 175 }
        )
    }

    on total_seconds() {
        return sum(tracks() |> pluck("secs"))
    }

    on by_artist(artist: String) {
        return tracks() |> filter(t => t.artist == artist) |> pluck("title")
    }

    on longest() {
        return tracks() |> max_by("secs")
    }

    on titles_sorted() {
        return tracks() |> sort_by("secs", "desc") |> pluck("title")
    }
}

cell test PlaylistTest {
    rules {
        assert total_seconds() == 810
        assert len(by_artist("Nim")) == 2
        assert by_artist("Nim")[0] == "Aurora"
        assert longest().title == "Cinder"
        assert titles_sorted()[0] == "Cinder"
        assert titles_sorted()[3] == "Dune"
    }
}