package phrasebook

import (
	"context"
	"fmt"
	"strings"
	"unicode"
	"unicode/utf8"

	"git.golem15.com/golem15/summercms/backpack"
	"git.golem15.com/golem15/summercms/pact"
	"git.golem15.com/golem15/summercms/towel"
)

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

// 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
}

// 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()
	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.cat.lookup(locale, key)
	if !ok {
		return key
	}
	return interpolate(e.text, params)
}

// Choice selects a translation for key. Plural selection is added in a later
// task; a non-plural value is returned as Get would.
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 {
	_ = count
	return t.GetIn(locale, key, params)
}

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:]
}