package caldata

import (
	"time"

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

// 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 {
		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 := 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.
	// Compute the pure temporal (no sanctoral) to get the day's ferial slug.
	if sel.Form != "old" && day.Observed.Layer != "temporal" &&
		day.WeekdayCycle != "" && date.Weekday() != time.Sunday {
		temp := calendar.Compute(date, sel, nil)
		if temp.Observed.Layer == "temporal" {
			if r := TemporalReadings("new", temp.Observed.Slug+"-"+day.WeekdayCycle); len(r) > 0 {
				return r
			}
		}
	}
	// EF: a green-season weekday with no proper Mass repeats the preceding Sunday.
	if sel.Form == "old" && day.Observed.Layer == "temporal" && date.Weekday() != time.Sunday {
		sun := date.AddDate(0, 0, -int(date.Weekday())) // preceding Sunday (Sunday = 0)
		sd := calendar.Compute(sun, sel, layers)
		return TemporalReadings(sel.Form, sd.Observed.Slug)
	}
	return nil
}