package phrasebook

import (
	"context"
	"fmt"
	"log/slog"
	"strconv"
	"strings"
	"sync"
	"unicode"
	"unicode/utf8"

	"git.golem15.com/golem15/summercms/backpack"
	"git.golem15.com/golem15/summercms/pact"
	"git.golem15.com/golem15/summercms/towel"
	"github.com/nicksnyder/go-i18n/v2/i18n"
	"github.com/nicksnyder/go-i18n/v2/i18n/template"
	"golang.org/x/text/language"
)

const (
	defaultLocale   = "en"
	defaultFallback = "en"
)

var (
	bundleCache   sync.Map // locale -> *i18n.Bundle
	categoryCache sync.Map // locale -> []string
	identityParse = template.IdentityParser{}
	pluralSamples = []any{
		0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
		20, 21, 22, 23, 24, 25, 100, 101, 102, 111, 1000, 1000000,
		"0.0", "0.1", "0.5", "1.0", "1.1", "1.5", "2.0", "2.5", "10.0", "100.0",
	}
	categoryMessage = &i18n.Message{
		ID:    "phrasebook.plural.category",
		Zero:  "zero",
		One:   "one",
		Two:   "two",
		Few:   "few",
		Many:  "many",
		Other: "other",
	}
)

// Options configures an app-scoped translator.
type Options struct {
	Locale     string
	Fallback   string
	Production bool
}

// Translator resolves namespaced translation keys from a loaded catalog.
type Translator struct {
	cat        *Catalog
	locale     string
	fallback   string
	production bool
	missing    sync.Map
}

// NewTranslator returns a translator that reads from cat. Empty locale or
// fallback values become the framework defaults en/en.
func NewTranslator(cat *Catalog, opts Options) *Translator {
	if cat == nil {
		cat = NewCatalog()
	}
	locale := strings.TrimSpace(opts.Locale)
	if locale == "" {
		locale = defaultLocale
	}
	fallback := strings.TrimSpace(opts.Fallback)
	if fallback == "" {
		fallback = defaultFallback
	}
	return &Translator{
		cat:        cat,
		locale:     locale,
		fallback:   fallback,
		production: opts.Production,
	}
}

// Activate loads HasLang catalogs in plugin order, then publishes one
// Translator on app before Boot. app.locale and app.fallback_locale default to en.
func Activate[P interface{ ID() string }](app *backpack.App, plugins []P) error {
	if app == nil {
		return fmt.Errorf("phrasebook: app is nil")
	}
	cat := NewCatalog()
	if err := cat.Load("lagoon", systemLangFS); err != nil {
		return err
	}
	for _, p := range plugins {
		hl, ok := any(p).(pact.HasLang)
		if !ok {
			continue
		}
		if err := cat.Load(p.ID(), hl.LangFS()); err != nil {
			return err
		}
	}
	opts := Options{Locale: defaultLocale, Fallback: defaultFallback}
	if app.Config != nil {
		if v := strings.TrimSpace(app.Config.String("app.locale")); v != "" {
			opts.Locale = v
		}
		if v := strings.TrimSpace(app.Config.String("app.fallback_locale")); v != "" {
			opts.Fallback = v
		}
		opts.Production = app.Config.Environment() == "production"
	}
	if err := app.Publish(NewTranslator(cat, opts)); err != nil {
		return fmt.Errorf("phrasebook: %w", err)
	}
	return nil
}

// Get returns the translation for key using the request locale when present,
// otherwise the configured app locale.
func (t *Translator) Get(ctx context.Context, key string, params map[string]string) string {
	return t.GetIn(t.localeFrom(ctx), key, params)
}

// GetIn looks up key in an explicit locale.
func (t *Translator) GetIn(locale, key string, params map[string]string) string {
	if t == nil {
		return key
	}
	e, _, ok := t.find(locale, key)
	if !ok {
		return key
	}
	text := e.text
	if text == "" && e.plurals != nil {
		text = e.plurals["other"]
	}
	return interpolate(text, params)
}

// Choice selects a plural form for key using CLDR rules or Laravel pipe conditions.
func (t *Translator) Choice(ctx context.Context, key string, count any, params map[string]string) string {
	return t.ChoiceIn(t.localeFrom(ctx), key, count, params)
}

// ChoiceIn is the explicit-locale form of Choice.
func (t *Translator) ChoiceIn(locale, key string, count any, params map[string]string) string {
	if t == nil {
		return key
	}
	e, found, ok := t.find(locale, key)
	if !ok {
		return key
	}
	text := e.text
	switch {
	case len(e.pipes) > 0:
		text = selectPipe(e.pipes, found, count)
	case e.plurals != nil:
		text = selectMap(e.plurals, found, count)
	}
	return interpolate(text, withCount(params, count))
}

func (t *Translator) find(locale, key string) (entry, string, bool) {
	if t == nil {
		return entry{}, locale, false
	}
	fallback := defaultFallback
	if t.fallback != "" {
		fallback = t.fallback
	}
	for _, step := range fallbackChain(locale, fallback) {
		if e, ok := t.cat.lookup(step, key); ok {
			return e, step, true
		}
	}
	t.logMissing(key)
	return entry{}, locale, false
}

func (t *Translator) logMissing(key string) {
	if t.production {
		return
	}
	if _, loaded := t.missing.LoadOrStore(key, struct{}{}); loaded {
		return
	}
	slog.Warn("phrasebook: missing translation key", "key", key)
}

func fallbackChain(requested, fallback string) []string {
	out := make([]string, 0, 4)
	seen := make(map[string]struct{}, 4)
	add := func(s string) {
		s = strings.TrimSpace(s)
		if s == "" {
			return
		}
		if _, ok := seen[s]; ok {
			return
		}
		seen[s] = struct{}{}
		out = append(out, s)
	}
	add(requested)
	if tag, err := language.Parse(requested); err == nil {
		add(tag.String())
		for p := tag.Parent(); !p.IsRoot(); p = p.Parent() {
			add(p.String())
		}
	} else if i := strings.IndexAny(requested, "-_"); i > 0 {
		add(requested[:i])
	}
	add(fallback)
	return out
}

func selectMap(plurals map[string]string, locale string, count any) string {
	cat, err := cldrCategory(locale, count)
	if err != nil {
		return plurals["other"]
	}
	if s, ok := plurals[cat]; ok {
		return s
	}
	return plurals["other"]
}

func selectPipe(parts []pipePart, locale string, count any) string {
	if n, ok := asFloat(count); ok {
		for _, p := range parts {
			if p.exact != nil && n == *p.exact {
				return p.text
			}
			if p.lo != nil && n >= *p.lo && (p.hi == nil || n <= *p.hi) {
				return p.text
			}
		}
	}
	cat, err := cldrCategory(locale, count)
	if err != nil {
		cat = "other"
	}
	var other, last string
	for _, p := range parts {
		last = p.text
		if p.cat == cat {
			return p.text
		}
		if p.cat == "other" {
			other = p.text
		}
	}
	if other != "" {
		return other
	}
	return last
}

func cldrCategory(locale string, count any) (string, error) {
	if strings.TrimSpace(locale) == "" {
		locale = defaultLocale
	}
	loc := i18n.NewLocalizer(bundleFor(locale), locale)
	return loc.Localize(&i18n.LocalizeConfig{
		DefaultMessage: categoryMessage,
		PluralCount:    coercePluralCount(count),
		TemplateParser: identityParse,
	})
}

func bundleFor(locale string) *i18n.Bundle {
	if v, ok := bundleCache.Load(locale); ok {
		return v.(*i18n.Bundle)
	}
	tag, err := language.Parse(locale)
	if err != nil {
		tag = language.English
	}
	b := i18n.NewBundle(tag)
	actual, _ := bundleCache.LoadOrStore(locale, b)
	return actual.(*i18n.Bundle)
}

func coercePluralCount(count any) any {
	switch count.(type) {
	case float32, float64:
		return formatCount(count)
	default:
		return count
	}
}

func cldrCategories(locale string) ([]string, map[string]struct{}, error) {
	if v, ok := categoryCache.Load(locale); ok {
		ordered := v.([]string)
		return ordered, setFrom(ordered), nil
	}
	seen := make(map[string]struct{})
	for _, n := range pluralSamples {
		cat, err := cldrCategory(locale, n)
		if err != nil {
			return nil, nil, err
		}
		seen[cat] = struct{}{}
	}
	seen["other"] = struct{}{}
	ordered := make([]string, 0, len(cldrOrder))
	for _, cat := range cldrOrder {
		if _, ok := seen[cat]; ok {
			ordered = append(ordered, cat)
		}
	}
	categoryCache.Store(locale, ordered)
	return ordered, seen, nil
}

func cldrCategorySet(locale string) (map[string]struct{}, error) {
	_, set, err := cldrCategories(locale)
	return set, err
}

func setFrom(vals []string) map[string]struct{} {
	out := make(map[string]struct{}, len(vals))
	for _, v := range vals {
		out[v] = struct{}{}
	}
	return out
}

func withCount(params map[string]string, count any) map[string]string {
	out := make(map[string]string, len(params)+1)
	for k, v := range params {
		out[k] = v
	}
	if _, ok := out["count"]; !ok {
		out["count"] = formatCount(count)
	}
	return out
}

func formatCount(count any) string {
	switch v := count.(type) {
	case int:
		return strconv.Itoa(v)
	case int8:
		return strconv.FormatInt(int64(v), 10)
	case int16:
		return strconv.FormatInt(int64(v), 10)
	case int32:
		return strconv.FormatInt(int64(v), 10)
	case int64:
		return strconv.FormatInt(v, 10)
	case uint:
		return strconv.FormatUint(uint64(v), 10)
	case uint64:
		return strconv.FormatUint(v, 10)
	case float32:
		return formatFloat(float64(v))
	case float64:
		return formatFloat(v)
	default:
		return fmt.Sprint(v)
	}
}

func formatFloat(v float64) string {
	if v == float64(int64(v)) {
		return strconv.FormatInt(int64(v), 10)
	}
	return strconv.FormatFloat(v, 'f', -1, 64)
}

func asFloat(count any) (float64, bool) {
	switch v := count.(type) {
	case int:
		return float64(v), true
	case int8:
		return float64(v), true
	case int16:
		return float64(v), true
	case int32:
		return float64(v), true
	case int64:
		return float64(v), true
	case uint:
		return float64(v), true
	case uint64:
		return float64(v), true
	case float32:
		return float64(v), true
	case float64:
		return v, true
	default:
		return 0, false
	}
}

func (t *Translator) localeFrom(ctx context.Context) string {
	if loc, ok := towel.Locale(ctx); ok {
		if loc = strings.TrimSpace(loc); loc != "" {
			return loc
		}
	}
	if t == nil || t.locale == "" {
		return defaultLocale
	}
	return t.locale
}

func interpolate(text string, params map[string]string) string {
	if text == "" || len(params) == 0 {
		return text
	}
	type pair struct {
		placeholder string
		value       string
	}
	pairs := make([]pair, 0, len(params)*3)
	for name, value := range params {
		name = strings.TrimPrefix(name, ":")
		if name == "" {
			continue
		}
		pairs = append(pairs,
			pair{placeholder: ":" + ucfirst(name), value: ucfirst(value)},
			pair{placeholder: ":" + strings.ToUpper(name), value: strings.ToUpper(value)},
			pair{placeholder: ":" + name, value: value},
		)
	}
	for i := 1; i < len(pairs); i++ {
		j := i
		for j > 0 && len(pairs[j].placeholder) > len(pairs[j-1].placeholder) {
			pairs[j], pairs[j-1] = pairs[j-1], pairs[j]
			j--
		}
	}
	for _, p := range pairs {
		text = strings.ReplaceAll(text, p.placeholder, p.value)
	}
	return text
}

func ucfirst(s string) string {
	if s == "" {
		return s
	}
	r, size := utf8.DecodeRuneInString(s)
	if r == utf8.RuneError && size == 1 {
		return s
	}
	return string(unicode.ToUpper(r)) + s[size:]
}