package language

import (
	"errors"
	"regexp"
	"slices"
	"strings"
)

var (
	ErrInvalidLanguage     = errors.New("invalid language tag")
	ErrUnsupportedLanguage = errors.New("unsupported language")
	ErrNoDefaultLanguage   = errors.New("the site has no default language")
)

const (
	Unassigned   = ""
	MaxTagLength = 35
)

var supported = []string{"en", "en-GB", "en-US", "fr", "fr-CA", "pt", "pt-BR", "es", "de", "ar"}

var tagPattern = regexp.MustCompile(`^([A-Za-z]{2,3})(?:-([A-Za-z]{2}))?$`)

func Supported() []string {
	return slices.Clone(supported)
}

func Normalize(tag string) (string, error) {
	parts := tagPattern.FindStringSubmatch(strings.TrimSpace(tag))
	if parts == nil {
		return "", ErrInvalidLanguage
	}
	normalized := strings.ToLower(parts[1])
	if parts[2] != "" {
		normalized += "-" + strings.ToUpper(parts[2])
	}
	if !slices.Contains(supported, normalized) {
		return "", ErrUnsupportedLanguage
	}
	return normalized, nil
}

type Suggestion struct {
	Tag         string
	Found       bool
	Substituted bool
}

func Suggest(locale *string) Suggestion {
	if locale == nil {
		return Suggestion{}
	}
	tag, err := Normalize(*locale)
	if err == nil {
		return Suggestion{Tag: tag, Found: true}
	}
	if !errors.Is(err, ErrUnsupportedLanguage) {
		return Suggestion{}
	}
	base, _, _ := strings.Cut(strings.TrimSpace(*locale), "-")
	if fallback, err := Normalize(base); err == nil {
		return Suggestion{Tag: fallback, Found: true, Substituted: true}
	}
	return Suggestion{}
}

type SiteLanguage struct {
	SiteID    uint32
	Tag       string
	IsDefault bool
	Enabled   bool
	Confirmed bool
}