package caldata

import (
	"sort"
	"strings"
	"time"

	"github.com/lukaszkasprzak/lectio/internal/calendar"
)

var partOrder = map[string]int{"first": 0, "psalm": 1, "second": 2, "acclamation": 3, "gospel": 4}

// ofFerial returns the day's Ordinary-Form ferial (weekday) readings, or nil.
func ofFerial(sel calendar.Selection, date time.Time, day calendar.LiturgicalDay) []calendar.Reading {
	if day.WeekdayCycle == "" || date.Weekday() == time.Sunday {
		return nil
	}
	if temp := calendar.Compute(date, sel, nil); temp.Observed.Layer == "temporal" {
		return TemporalReadings("new", temp.Observed.Slug+"-"+day.WeekdayCycle)
	}
	return nil
}

// Readings resolves a day's Mass readings: the observed celebration's inline
// propers, else the temporal lectionary for its slug, else -- for an EF
// weekday with no proper Mass -- the preceding Sunday's Mass (the 1962 rule
// that green-season ferias repeat the Sunday). Shared by the CLI (cli.dayReadings
// delegates here) and calfeed.Build (injected as its readings func).
func Readings(sel calendar.Selection, layers []calendar.Layer, date time.Time, day calendar.LiturgicalDay) []calendar.Reading {
	var rs []calendar.Reading
	for _, m := range day.Observed.Masses {
		rs = append(rs, m.Readings...)
	}
	if len(rs) > 0 {
		// OF: a memorial with only a PROPER gospel (or only a proper first) takes
		// the missing reading from the day's ferial -- e.g. the Guardian Angels are
		// the ferial first reading + their proper gospel (Matt 18), and St Barnabas
		// is his proper first (Acts 11) + the ferial gospel. A fully-proper feast
		// (first AND gospel present) is left untouched.
		have := map[string]bool{}
		for _, r := range rs {
			have[r.Part] = true
		}
		if sel.Form != "old" && !(have["first"] && have["gospel"]) {
			for _, fr := range ofFerial(sel, date, day) {
				if p := fr.Part; !have[p] && (p == "first" || p == "psalm" || p == "gospel") {
					rs = append(rs, fr)
					have[p] = true
				}
			}
			sort.SliceStable(rs, func(i, j int) bool { return partOrder[rs[i].Part] < partOrder[rs[j].Part] })
		}
		return rs
	}
	// temporal table: EF by bare slug; OF by slug+cycle. Sundays & solemnities
	// use the 3-year Sunday cycle (A/B/C); ferial weekdays use the 2-year
	// weekday cycle (I/II). Sunday-slugs and weekday-slugs are disjoint, so
	// trying both cycle suffixes is unambiguous.
	if sel.Form == "old" {
		if r := efBVMSaturdayReadings(day); len(r) > 0 {
			return r
		}
		if r := TemporalReadings("old", day.Observed.Slug); len(r) > 0 {
			return r
		}
	} else {
		for _, cyc := range []string{day.SundayCycle, day.WeekdayCycle} {
			if cyc == "" {
				continue
			}
			if r := TemporalReadings("new", day.Observed.Slug+"-"+cyc); len(r) > 0 {
				return r
			}
		}
	}
	// OF: a sanctoral memorial / optional memorial with no proper readings of its
	// own reads the FERIAL (weekday) readings of the day -- the ordinary OF rule.
	if sel.Form != "old" && day.Observed.Layer != "temporal" {
		if r := ofFerial(sel, date, day); len(r) > 0 {
			return r
		}
	}
	// EF: a green-season weekday with no proper Mass repeats the preceding
	// Sunday's Mass. Use the Sunday's TEMPORAL slug (not its observed) so the
	// repeat still resolves when that Sunday was a feast (e.g. the Purification).
	if sel.Form == "old" && day.Observed.Layer == "temporal" && date.Weekday() != time.Sunday {
		sun := date.AddDate(0, 0, -int(date.Weekday())) // preceding Sunday (Sunday = 0)
		return TemporalReadings(sel.Form, calendar.TemporalSlug(sun, sel))
	}
	return nil
}

// efBVMSaturdayReadings returns the Mass of Our Lady on Saturday, when that is
// the day's office.
//
// RG 78 keeps the office on a Saturday whose feria is IV class (see
// temporal_ef.go, which gives the day its white colour). RG 309(a) then says
// which Mass is said: "Missae de sancta Maria in sabbato ... iuxta temporum
// diversitatem" -- the Missal prints five formularies and the season selects
// among them. Without this the day was kept as Our Lady's but read the feria's
// Mass, so a Saturday in Septuagesima announced Our Lady and then read the
// parable of the labourers.
//
// Citations are colitur's, which verified each against both photographic scans
// of the 1962 Missal; see its lib/rites/rite_ef/lectionary_ef.ml,
// bvm_saturday_citations, for the per-formulary scan references.
//
// The Advent formulary is included and is STRUCTURALLY UNREACHABLE as the
// Saturday office: Advent has no IV-class ferias, so the office never falls
// there. It is kept because RG 309's subject is the Masses themselves, not
// only the days they land on -- the Mass exists -- and because a missing
// branch would silently fall through if the rank rules ever changed.
func efBVMSaturdayReadings(day calendar.LiturgicalDay) []calendar.Reading {
	// The office, not merely the day: a Saturday IV-class feria that nothing
	// outranked. A sanctoral feast that won the day keeps its own readings, so
	// the observed slug must still be the temporal one -- which the office
	// deliberately reuses rather than replacing (see temporal_ef.go).
	if day.Weekday != time.Saturday || day.Observed.Rank != calendar.RankClass4 {
		return nil
	}
	if !strings.HasPrefix(day.Observed.Slug, "ef-") || !strings.HasSuffix(day.Observed.Slug, "-saturday") {
		return nil
	}
	first, gospel := "", ""
	switch day.Season {
	case calendar.Advent:
		first, gospel = "Isa 7:10-15", "Luke 1:26-38"
	case calendar.Christmas:
		first, gospel = "Titus 3:4-7", "Luke 2:15-20"
	case calendar.TimeAfterEpiphany:
		// The Christmastide formulary runs on until the Purification (2
		// February), not merely to the end of Christmas Time.
		if m := day.Date.Month(); m == time.January || (m == time.February && day.Date.Day() <= 2) {
			first, gospel = "Titus 3:4-7", "Luke 2:15-20"
		} else {
			first, gospel = "Ecclus 24:14-16", "Luke 11:27-28"
		}
	case calendar.Easter_:
		first, gospel = "Ecclus 24:14-16", "John 19:25-27"
	default: // Septuagesima, Lent, Passiontide, Time after Pentecost
		first, gospel = "Ecclus 24:14-16", "Luke 11:27-28"
	}
	return []calendar.Reading{
		{Part: "first", Citation: first},
		{Part: "gospel", Citation: gospel},
	}
}