rite(ef): season boundaries per RG 71-77

Christmas Time runs to 13 January inclusive (RG 72-73) and time after Epiphany
opens on 14 January (RG 77), diverging from lectio, which starts
time-after-epiphany at 6 January. Holy Saturday stays in Passiontide: the
Easter Vigil is a night Mass, and a per-day calendar assigns a date by the
season governing its day-hours.

1 files changed, 48 insertions, 0 deletions

diff --git a/lib/rites/rite_ef/temporal_ef.ml b/lib/rites/rite_ef/temporal_ef.ml
new file mode 100644
index 0000000..c975316
--- /dev/null
+++ b/lib/rites/rite_ef/temporal_ef.ml
@@ -0,0 +1,48 @@
+(* EF (1962) temporal cycle. Every boundary and rank rule cites its Rubricae
+   Generales paragraph; see docs/research/rules-register.md §3-§4. *)
+
+open Colitur_kernel
+open Vocab_ef
+
+let mk y m d =
+  match Date.make ~year:y ~month:m ~day:d with
+  | Ok t -> t
+  | Error e -> failwith ("temporal_ef: " ^ e)
+
+let weekday_index d =
+  match Date.weekday d with
+  | Date.Sun -> 0 | Date.Mon -> 1 | Date.Tue -> 2 | Date.Wed -> 3
+  | Date.Thu -> 4 | Date.Fri -> 5 | Date.Sat -> 6
+
+(* The Sunday on or before [d]. *)
+let sunday_on_or_before d = Date.add_days d (-(weekday_index d))
+
+(* RG 71: Advent I is the Sunday nearest 30 November -- equivalently the fourth
+   Sunday before Christmas, i.e. three weeks before the last Sunday on or before
+   24 December. *)
+let advent_start y = Date.add_days (sunday_on_or_before (mk y 12 24)) (-21)
+let year_start = advent_start
+
+let before a b = Date.compare a b < 0
+let on_or_after a b = Date.compare a b >= 0
+
+(* RG 71-77. Tested in chronological order within the civil year. *)
+let season d =
+  let y = Date.year d in
+  let easter = Computus.gregorian_easter y in
+  let advent_this = advent_start y in
+  let christmas_this = mk y 12 25 in
+  let jan14 = mk y 1 14 in
+  let septuagesima_sunday = Date.add_days easter (-63) in
+  let ash_wednesday = Date.add_days easter (-46) in
+  let passion_sunday = Date.add_days easter (-14) in
+  let paschal_end = Date.add_days easter 55 in
+  if on_or_after d advent_this && before d christmas_this then Advent (* RG 71 *)
+  else if on_or_after d christmas_this then Christmastide (* RG 72-73: 25-31 Dec *)
+  else if before d jan14 then Christmastide (* RG 72-73: 1-13 Jan inclusive *)
+  else if before d septuagesima_sunday then Time_after_epiphany (* RG 77: from 14 Jan *)
+  else if before d ash_wednesday then Septuagesima (* RG 73 *)
+  else if before d passion_sunday then Lent (* RG 74 *)
+  else if before d easter then Passiontide (* RG 75; Holy Saturday included *)
+  else if Date.compare d paschal_end <= 0 then Paschaltide (* RG 76 *)
+  else Time_after_pentecost (* RG 77 *)