// Package naming renders human-readable liturgical day names from the calendar // engine's computed slugs, in any language. English is the built-in baseline // (builtinEN, below); every other language is data: an embedded lang/
.ini
// shipped with lectio, and/or a user file at /.ini that
// overrides it key by key. A partial translation never breaks -- any string a
// language omits falls back to English.
//
// Two things are localised here: the generated TEMPORAL day names (e.g. "3rd
// Sunday in Ordinary Time"), composed from a small vocabulary plus per-language
// format templates so word order and grammatical case can differ; and the
// display name of any celebration (CelebrationName), which prefers the
// calendar entry's own name. and falls back through English, Latin, and
// finally the humanized slug. Saint names themselves live in the calendar data
// (name.), not here.
package naming

import (
	"embed"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"sync"

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

//go:embed lang
var langFS embed.FS

// Table is one language's temporal-naming data. Every field is optional in a
// language file: a missing entry falls back to the English baseline (for maps,
// per key), so a translator fills in only what they want to change.
type Table struct {
	Weekdays   map[string]string // mon,tue,wed,thu,fri,sat,sun -> weekday name
	NamedDays  map[string]string // temporal slug -> proper name (Good Friday, ...)
	Seasons    map[string]string // season slug -> localised season name
	SeasonPrep map[string]string // season slug -> preposition joining it to a week/Sunday
	Months     []string          // 12 month names (index 0 = January), for dated ferias
	Templates  map[string]string // template id -> format with {ord}{wd}{season}{prep}{day}{month}
	Ordinals   map[string]string // "1".."40" -> localised ordinal (optional; overrides OrdinalFmt)
	OrdinalFmt string            // printf-style fallback ordinal, e.g. "%d." (optional)
}

// ---- temporal slug patterns (the calendar engine's own slug shapes) ---------

var (
	reSeasonSun = regexp.MustCompile(`^(.+)-sunday-(\d+)$`)                 // -sunday-N (all numbered Sundays)
	reOctave    = regexp.MustCompile(`^easter-octave-([a-z]+)$`)            // Octave of Easter weekday
	reAfterAsh  = regexp.MustCompile(`^lent-after-ashes-([a-z]+)$`)         // Thu/Fri/Sat after Ash Wednesday
	reHolyWeek  = regexp.MustCompile(`^holy-week-([a-z]+)$`)                // Mon-Wed of Holy Week
	reAdventDec = regexp.MustCompile(`^advent-dec-(\d+)$`)                  // late-Advent dated feria
	reXmasDate  = regexp.MustCompile(`^christmas-(dec|jan)-(\d+)$`)         // Christmastide dated feria
	reAftEpiph  = regexp.MustCompile(`^christmas-after-epiphany-([a-z]+)$`) // weekday after Epiphany
	reEmber     = regexp.MustCompile(`^(september|advent)-ember-([a-z]+)$`) // Ember day
	reWeekday   = regexp.MustCompile(`^(.+)-(\d+)-([a-z]+)$`)               // --
	rePlacehold = regexp.MustCompile(`\{[a-z]+\}`)                          // leftover {token} cleanup
)

// weekdayAbbrev maps any weekday token the slugs use (abbreviated or full) to
// the canonical three-letter key the Table's Weekdays map is keyed by.
var weekdayAbbrev = map[string]string{
	"mon": "mon", "tue": "tue", "wed": "wed", "thu": "thu", "fri": "fri", "sat": "sat", "sun": "sun",
	"monday": "mon", "tuesday": "tue", "wednesday": "wed", "thursday": "thu",
	"friday": "fri", "saturday": "sat", "sunday": "sun",
}

// builtinEN is the English baseline every other language overlays. The season
// name/preposition and ordinal for English are computed (enSeasonName,
// enSeasonPrep, enOrdinal) rather than tabulated, so unlisted seasons still
// read correctly; a language file supplies Seasons/SeasonPrep/Ordinals to
// override them.
var builtinEN = Table{
	Weekdays: map[string]string{
		"mon": "Monday", "tue": "Tuesday", "wed": "Wednesday", "thu": "Thursday",
		"fri": "Friday", "sat": "Saturday", "sun": "Sunday",
	},
	NamedDays: map[string]string{
		"triduum-thu": "Holy Thursday", "triduum-fri": "Good Friday", "triduum-sat": "Holy Saturday",
		"maundy-thursday": "Holy Thursday", "good-friday": "Good Friday", "holy-saturday": "Holy Saturday",
		"palm-sunday": "Palm Sunday", "passion-sunday": "Passion Sunday", "low-sunday": "Second Sunday of Easter",
		"trinity-sunday": "The Most Holy Trinity", "trinity": "Trinity Sunday",
		"corpus-christi": "The Body and Blood of Christ", "sacred-heart": "The Most Sacred Heart of Jesus",
		"christ-the-king": "Our Lord Jesus Christ, King of the Universe",
		"easter-sunday":   "Easter Sunday", "pentecost": "Pentecost Sunday", "ascension": "The Ascension of the Lord",
		"holy-family": "The Holy Family of Jesus, Mary and Joseph", "baptism-of-the-lord": "The Baptism of the Lord",
		"epiphany": "The Epiphany of the Lord", "christmas": "The Nativity of the Lord", "nativity": "The Nativity of the Lord",
		"circumcision": "The Circumcision of the Lord", "ash-wednesday": "Ash Wednesday",
		"ascension-vigil": "Vigil of the Ascension", "pentecost-vigil": "Vigil of Pentecost",
		"christmas-sunday-sun":                   "Second Sunday after the Nativity",
		"mary-mother-of-god-octave-of-christmas": "Mary, the Holy Mother of God",
	},
	Months: []string{"January", "February", "March", "April", "May", "June",
		"July", "August", "September", "October", "November", "December"},
	Templates: map[string]string{
		"sunday":          "{ord} Sunday {prep} {season}",
		"weekday":         "{wd} of the {ord} Week {prep} {season}",
		"weekday_no_week": "{wd} {prep} {season}",
		"octave_easter":   "{wd} in the Octave of Easter",
		"after_ashes":     "{wd} after Ash Wednesday",
		"holy_week":       "{wd} of Holy Week",
		"after_epiphany":  "{wd} after the Epiphany",
		"ember":           "Ember {wd} of {season}",
		"passion_week":    "{wd} of Passion Week",
		"date":            "{month} {day}",
	},
	Seasons:    map[string]string{},
	SeasonPrep: map[string]string{},
	Ordinals:   map[string]string{},
}

// ---- table resolution + caching ---------------------------------------------

var (
	tblMu    sync.Mutex
	tblCache = map[string]Table{}
	userDir  string
)

// SetUserDir points naming at the drop-in dir holding user language files
// (/.ini) and invalidates the cache. Empty string disables it.
func SetUserDir(dir string) {
	tblMu.Lock()
	userDir = dir
	tblCache = map[string]Table{}
	tblMu.Unlock()
}

// tableFor returns the merged table for lang: the English baseline, overlaid by
// the embedded lang/.ini (if lectio ships one), overlaid by the user's
// /.ini (if present).
func tableFor(lang string) Table {
	tblMu.Lock()
	defer tblMu.Unlock()
	if t, ok := tblCache[lang]; ok {
		return t
	}
	t := builtinEN.clone()
	if lang != "" && lang != "en" {
		if data, err := langFS.ReadFile("lang/" + lang + ".ini"); err == nil {
			t.overlay(parseTable(data))
		}
	}
	if userDir != "" && lang != "" {
		if data, err := os.ReadFile(filepath.Join(userDir, lang+".ini")); err == nil {
			t.overlay(parseTable(data))
		}
	}
	tblCache[lang] = t
	return t
}

func (t Table) clone() Table {
	c := Table{
		Weekdays: cloneMap(t.Weekdays), NamedDays: cloneMap(t.NamedDays),
		Seasons: cloneMap(t.Seasons), SeasonPrep: cloneMap(t.SeasonPrep),
		Templates: cloneMap(t.Templates), Ordinals: cloneMap(t.Ordinals),
		OrdinalFmt: t.OrdinalFmt,
	}
	c.Months = append([]string(nil), t.Months...)
	return c
}

// overlay copies o's non-empty entries onto t (per key), so a partial language
// file overrides only the strings it provides.
func (t *Table) overlay(o Table) {
	mergeMap(t.Weekdays, o.Weekdays)
	mergeMap(t.NamedDays, o.NamedDays)
	mergeMap(t.Seasons, o.Seasons)
	mergeMap(t.SeasonPrep, o.SeasonPrep)
	mergeMap(t.Templates, o.Templates)
	mergeMap(t.Ordinals, o.Ordinals)
	if o.OrdinalFmt != "" {
		t.OrdinalFmt = o.OrdinalFmt
	}
	for i, m := range o.Months {
		if m != "" && i < len(t.Months) {
			t.Months[i] = m
		}
	}
}

func cloneMap(m map[string]string) map[string]string {
	c := make(map[string]string, len(m))
	for k, v := range m {
		c[k] = v
	}
	return c
}

// mergeMap copies every entry of src over dst, including empty values: an empty
// override is respected where it is meaningful (a season_prep a language leaves
// blank because it joins by grammatical case) and harmless elsewhere, since the
// getters fall back to English when a looked-up string is empty.
func mergeMap(dst, src map[string]string) {
	for k, v := range src {
		dst[k] = v
	}
}

// ---- public API -------------------------------------------------------------

// DayName renders a temporal day slug as a proper name in lang, e.g.
// DayName("ordinary-sunday-11", "en") == "11th Sunday in Ordinary Time".
func DayName(slug, lang string) string {
	return tableFor(lang).day(slug)
}

// CelebrationName is a celebration's display name in lang: its own name.
// if present, else name.en, else name.la, else the humanized temporal slug.
// Returns "" only for an unnamed celebration with an empty slug (the caller
// decides how to render a bare feria).
func CelebrationName(lang string, c calendar.Celebration) string {
	if lang != "" {
		if n := c.Name[lang]; n != "" {
			return n
		}
	}
	if n := c.Name["en"]; n != "" {
		return n
	}
	if n := c.Name["la"]; n != "" {
		return n
	}
	if c.Slug == "" {
		return ""
	}
	return DayName(c.Slug, lang)
}

// ---- composition ------------------------------------------------------------

func (t Table) day(slug string) string {
	s := strings.TrimPrefix(slug, "ef-")
	if n, ok := t.NamedDays[s]; ok {
		return n
	}
	if m := reSeasonSun.FindStringSubmatch(s); m != nil {
		return t.render("sunday", map[string]string{
			"ord": t.ordinal(atoi(m[2])), "prep": t.prep(m[1]), "season": t.season(m[1]),
		})
	}
	if m := reOctave.FindStringSubmatch(s); m != nil {
		return t.render("octave_easter", map[string]string{"wd": t.weekday(m[1])})
	}
	if m := reAfterAsh.FindStringSubmatch(s); m != nil {
		if weekdayAbbrev[m[1]] == "wed" {
			return t.NamedDays["ash-wednesday"] // the day the ferias hang off of
		}
		return t.render("after_ashes", map[string]string{"wd": t.weekday(m[1])})
	}
	if m := reHolyWeek.FindStringSubmatch(s); m != nil {
		return t.render("holy_week", map[string]string{"wd": t.weekday(m[1])})
	}
	if m := reAdventDec.FindStringSubmatch(s); m != nil {
		return t.render("date", map[string]string{"month": t.month(12), "day": m[1]})
	}
	if m := reXmasDate.FindStringSubmatch(s); m != nil {
		mon := 12
		if m[1] == "jan" {
			mon = 1
		}
		return t.render("date", map[string]string{"month": t.month(mon), "day": m[2]})
	}
	if m := reAftEpiph.FindStringSubmatch(s); m != nil {
		return t.render("after_epiphany", map[string]string{"wd": t.weekday(m[1])})
	}
	if m := reEmber.FindStringSubmatch(s); m != nil {
		return t.render("ember", map[string]string{"wd": t.weekday(m[2]), "season": t.season(m[1])})
	}
	if m := reWeekday.FindStringSubmatch(s); m != nil {
		if _, ok := weekdayAbbrev[m[3]]; ok {
			n := atoi(m[2])
			if n == 0 { // Passiontide's pre-Palm-Sunday week carries no number
				if m[1] == "passiontide" {
					return t.render("passion_week", map[string]string{"wd": t.weekday(m[3])})
				}
				return t.render("weekday_no_week", map[string]string{
					"wd": t.weekday(m[3]), "prep": t.prep(m[1]), "season": t.season(m[1]),
				})
			}
			return t.render("weekday", map[string]string{
				"wd": t.weekday(m[3]), "ord": t.ordinal(n), "prep": t.prep(m[1]), "season": t.season(m[1]),
			})
		}
	}
	return titleCase(strings.ReplaceAll(s, "-", " "))
}

// render fills a template's {tokens}, drops any left unfilled, and collapses
// whitespace -- so a language with an empty preposition (case-joined seasons)
// never leaves a double space.
func (t Table) render(id string, vars map[string]string) string {
	f := t.Templates[id]
	if f == "" {
		f = builtinEN.Templates[id]
	}
	for k, v := range vars {
		f = strings.ReplaceAll(f, "{"+k+"}", v)
	}
	f = rePlacehold.ReplaceAllString(f, "")
	return strings.Join(strings.Fields(f), " ")
}

func (t Table) weekday(tok string) string {
	if ab, ok := weekdayAbbrev[tok]; ok {
		if name := t.Weekdays[ab]; name != "" {
			return name
		}
	}
	return titleCase(tok)
}

func (t Table) month(n int) string {
	if n >= 1 && n <= len(t.Months) && t.Months[n-1] != "" {
		return t.Months[n-1]
	}
	return builtinEN.Months[n-1]
}

func (t Table) ordinal(n int) string {
	if s, ok := t.Ordinals[strconv.Itoa(n)]; ok {
		return s
	}
	if t.OrdinalFmt != "" {
		return fmt.Sprintf(t.OrdinalFmt, n)
	}
	return enOrdinal(n)
}

func (t Table) season(slug string) string {
	if s, ok := t.Seasons[slug]; ok {
		return s
	}
	return enSeasonName(slug)
}

func (t Table) prep(slug string) string {
	if p, ok := t.SeasonPrep[slug]; ok {
		return p // may be intentionally empty
	}
	return enSeasonPrep(slug)
}

// ---- English fallbacks (match the historical HumanizeSlug behaviour) ---------

func enSeasonName(slug string) string {
	if slug == "ordinary" {
		return "Ordinary Time"
	}
	if rest := strings.TrimPrefix(slug, "time-after-"); rest != slug {
		return titleCase(rest)
	}
	return titleCase(strings.ReplaceAll(slug, "-", " "))
}

func enSeasonPrep(slug string) string {
	if slug == "ordinary" {
		return "in"
	}
	if strings.HasPrefix(slug, "time-after-") {
		return "after"
	}
	return "of"
}

func enOrdinal(n int) string {
	s := strconv.Itoa(n)
	if n%100 >= 11 && n%100 <= 13 {
		return s + "th"
	}
	switch n % 10 {
	case 1:
		return s + "st"
	case 2:
		return s + "nd"
	case 3:
		return s + "rd"
	}
	return s + "th"
}

func titleCase(s string) string {
	small := map[string]bool{"of": true, "the": true, "in": true, "after": true, "before": true}
	words := strings.Fields(s)
	for i, w := range words {
		if i > 0 && small[w] {
			continue
		}
		if w != "" {
			words[i] = strings.ToUpper(w[:1]) + w[1:]
		}
	}
	return strings.Join(words, " ")
}

func atoi(s string) int { n, _ := strconv.Atoi(s); return n }

// ---- language-file parsing --------------------------------------------------

// parseTable reads a language INI into a (partial) Table. Sections:
//
//	[templates]   id = format
//	[weekdays]    mon..sun = name
//	[months]      1..12 = name
//	[seasons]      = name
//	[season_prep]  = preposition (may be empty)
//	[named]        = name
//	[ordinal]     format = %d.   |   1 = 1st, 2 = 2nd, ...
func parseTable(data []byte) Table {
	t := Table{
		Weekdays: map[string]string{}, NamedDays: map[string]string{},
		Seasons: map[string]string{}, SeasonPrep: map[string]string{},
		Templates: map[string]string{}, Ordinals: map[string]string{},
		Months: make([]string, 12),
	}
	secs, err := ini.Parse(data)
	if err != nil {
		return t
	}
	for _, s := range secs {
		for _, p := range s.Pairs {
			switch s.Name {
			case "templates":
				t.Templates[p.Key] = p.Val
			case "weekdays":
				if ab, ok := weekdayAbbrev[p.Key]; ok {
					t.Weekdays[ab] = p.Val
				}
			case "months":
				if i := atoi(p.Key); i >= 1 && i <= 12 {
					t.Months[i-1] = p.Val
				}
			case "seasons":
				t.Seasons[p.Key] = p.Val
			case "season_prep":
				t.SeasonPrep[p.Key] = p.Val
			case "named":
				t.NamedDays[p.Key] = p.Val
			case "ordinal":
				if p.Key == "format" {
					t.OrdinalFmt = p.Val
				} else {
					t.Ordinals[p.Key] = p.Val
				}
			}
		}
	}
	return t
}