open Colitur_kernel

(* Step 1: the observed celebration's own proper.
   Step 2: the day's own temporal slug.

   Nothing here encodes "Lent has daily propers": the presence of an entry in
   [lectionary] is the sole discriminator -- this function does not branch on
   season, rank, or any other field to decide whether a temporal slug "ought"
   to have its own Mass.

   The WARRANT for that shape is lectio's own observed behaviour only, not a
   confirmed Missal citation: Lent 1 Monday returns its own Ezech 34:11-16,
   while Advent, Christmas and post-Pentecost Mondays return their Sunday's
   Mass, in both streams. docs/research/rules-register.md records this
   openly as unconfirmed against the primary source ("EF reading-selection
   rules ... Have lectio's behaviour; confirm against the Missal's
   ferial-Mass rubrics when coding") -- that confirmation has not been done;
   do not read this comment as citing RG/the Missal for the SELECTION rule
   itself, only [Lectionary.find]'s presence-or-absence as the mechanism. *)
let readings ~lectionary ~observed ~temporal ~date:_ ~temporal_at:_ =
  match observed.Celebration.citations with
  | _ :: _ as cs -> cs
  | [] -> (
      match Lectionary.find lectionary temporal.Temporal.office.Celebration.slug with
      | Some cs -> cs
      | None -> [])