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package calendar
import (
"sort"
"strings"
"time"
)
// 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)
cands := []candidate{{
Cel: td.Cel, Temporal: true, Privileged: td.Privileged,
PrivFeria: td.PrivFeria, Sunday: td.Sunday, Season: td.Season,
}}
for slug, rc := range merged {
cel := buildCelebration(slug, rc)
when, ok := celebrationDate(cel, date.Year(), sel)
if !ok {
continue
}
// On band-2 privileged days only solemnities survive (and they transfer);
// on Sundays (band 6) only feasts and solemnities compete.
if td.Privileged && ofRankOrder(cel.Rank) < ofRankOrder(RankSolemnity) {
continue
}
if td.Sunday && ofRankOrder(cel.Rank) < ofRankOrder(RankFeast) {
continue
}
effective := transferIfImpeded(cel, when, sel)
if sameDay(effective, date) {
cands = append(cands, candidate{Cel: cel, Temporal: false, Season: td.Season})
}
}
obs, others := pick(cands)
day := LiturgicalDay{
Date: date, Season: td.Season, Week: td.Week, Weekday: date.Weekday(),
Observed: obs.Cel, Colour: colourOf(obs, td), ObservedBand: precedence(obs),
SundayCycle: sundayCycle(liturgicalYearStart(date)),
WeekdayCycle: weekdayCycle(liturgicalYearStart(date).Year() + 1),
}
for _, o := range others {
if o.Temporal {
continue // a superseded ferial/Sunday is not a commemoration
}
day.Others = append(day.Others, o.Cel)
}
return day
}
func colourOf(obs candidate, td temporalDay) Colour {
if obs.Cel.Colour != "" {
return obs.Cel.Colour
}
return td.Colour
}
// celebrationDate resolves a sanctoral celebration's date for the year.
func celebrationDate(cel Celebration, year int, sel Selection) (time.Time, bool) {
return resolveDate(cel.Date, year, Easter(year))
}
// transferIfImpeded moves a solemnity off a band-1/2 temporal day to the next
// free day. Non-solemnities are never transferred (they yield instead).
func transferIfImpeded(cel Celebration, when time.Time, sel Selection) time.Time {
if cel.Rank != RankSolemnity {
return when
}
day := when
for i := 0; i < 30; i++ {
b := temporal(day, sel)
band := precedence(candidate{
Cel: b.Cel, Temporal: true, Privileged: b.Privileged,
PrivFeria: b.PrivFeria, Sunday: b.Sunday, Season: b.Season,
})
if band <= 2 { // impeded by Triduum / a privileged day: push forward
day = day.AddDate(0, 0, 1)
continue
}
return day
}
return day
}
// buildCelebration types a RawCelebration.
func buildCelebration(slug string, rc RawCelebration) Celebration {
c := Celebration{Slug: strings.TrimSpace(slug), Name: map[string]string{}, Layer: rc.Fields["layer"]}
for k, v := range rc.Fields {
switch {
case k == "rank":
c.Rank = ParseRank(v)
case k == "class":
c.Class = ParseClass(v)
case k == "colour":
c.Colour = ParseColour(v)
case k == "date":
c.Date = DateSpec(v)
case strings.HasPrefix(k, "name."):
c.Name[strings.TrimPrefix(k, "name.")] = v
}
}
if c.Rank == "" {
c.Rank = RankFerial
}
if m := massFrom(rc.Fields); len(m.Readings) > 0 {
c.Masses = append(c.Masses, m)
}
var variants []string
for v := range rc.Variants {
variants = append(variants, v)
}
sort.Strings(variants)
for _, v := range variants {
mm := massFrom(rc.Variants[v])
mm.Variant = v
c.Masses = append(c.Masses, mm)
}
return c
}
// BuildCelebrationForTest exposes buildCelebration for cross-package data tests.
func BuildCelebrationForTest(slug string, rc RawCelebration) Celebration {
return buildCelebration(slug, rc)
}
var readingParts = []string{"first", "psalm", "second", "acclamation", "gospel"}
func massFrom(fields map[string]string) Mass {
var m Mass
for _, part := range readingParts {
if cit := fields["reading."+part]; cit != "" {
m.Readings = append(m.Readings, Reading{Part: part, Citation: cit})
}
}
return m
}
// liturgicalYearStart returns the First Sunday of Advent that opened the
// liturgical year containing date.
func liturgicalYearStart(date time.Time) time.Time {
a := adventStart(date.Year())
if date.Before(a) {
return adventStart(date.Year() - 1)
}
return a
}
// sundayCycle: the liturgical year's civil year (Advent year + 1) mod 3 →
// C(0), A(1), B(2).
func sundayCycle(start time.Time) string {
switch (start.Year() + 1) % 3 {
case 0:
return "C"
case 1:
return "A"
default:
return "B"
}
}
// weekdayCycle: odd liturgical-year civil year → I, even → II.
func weekdayCycle(year int) string {
if year%2 == 1 {
return "I"
}
return "II"
}
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