feat(calendar): Compute branches on Form (computeEF via temporalEF/precedenceEF)

1 files changed, 41 insertions, 3 deletions

diff --git a/internal/calendar/calendar.go b/internal/calendar/calendar.go
index 98dec43..e0f5217 100644
--- a/internal/calendar/calendar.go
+++ b/internal/calendar/calendar.go
@@ -6,11 +6,49 @@ import (
 	"time"
 )
 
-// Compute returns the Ordinary Form liturgical day for date under the given
-// Selection, with the ordered layer stack supplying celebrations. It is pure
-// and total: any valid Gregorian date yields a LiturgicalDay.
+// Compute returns the liturgical day for date under the given Selection, with
+// the ordered layer stack supplying celebrations. It is pure and total: any
+// valid Gregorian date yields a LiturgicalDay. Selection.Form "old" computes the
+// Extraordinary Form (1962); anything else computes the Ordinary Form.
 func Compute(date time.Time, sel Selection, layers []Layer) LiturgicalDay {
 	date = date.UTC().Truncate(24 * time.Hour)
+	if sel.Form == "old" {
+		return computeEF(date, sel, layers)
+	}
+	return computeOF(date, sel, layers)
+}
+
+// computeEF computes the Extraordinary Form (1962) day.
+func computeEF(date time.Time, sel Selection, layers []Layer) LiturgicalDay {
+	td := temporalEF(date)
+	merged := mergeLayers(layers)
+	cands := []candidate{{Cel: td.Cel, Temporal: true, Season: td.Season}}
+	for slug, rc := range merged {
+		cel := buildCelebration(slug, rc)
+		when, ok := celebrationDate(cel, date.Year(), sel)
+		if !ok {
+			continue
+		}
+		if sameDay(when, date) {
+			cands = append(cands, candidate{Cel: cel, Temporal: false, Season: td.Season})
+		}
+	}
+	obs, others := pickEF(cands)
+	day := LiturgicalDay{
+		Date: date, Season: td.Season, Week: td.Week, Weekday: date.Weekday(),
+		Observed: obs.Cel, Colour: colourOf(obs, td), ObservedBand: precedenceEF(obs),
+	}
+	for _, o := range others {
+		if o.Temporal {
+			continue
+		}
+		day.Others = append(day.Others, o.Cel)
+	}
+	return day
+}
+
+// computeOF computes the Ordinary Form day.
+func computeOF(date time.Time, sel Selection, layers []Layer) LiturgicalDay {
 	td := temporal(date, sel)
 	merged := mergeLayers(layers)