// Package locale defines a Locale type that represents a POSIX locale value, as
// required by desktop-entry-spec.
package locale

import "fmt"
import "strings"

type localeError string
func (err localeError) Error () string { return string(err) }

const (
	// ErrUnexpectedRune indicates an unexpected rune was encountered while
	// parsing a locale string.
	ErrUnexpectedRune = localeError("unexpected rune")
	// ErrLangEmpty indicates that a lang value was not specified.
	ErrLangEmpty = localeError("lang empty")
)

// Locale represents a POSIX locale value.
type Locale struct {
	Lang     string
	Country  string
	Encoding string
	Modifier string
}

// String returns the string representation of the Locale. Unspecified values
// are left out.
func (locale Locale) String () string {
	str := locale.Lang
	if locale.Country != "" {
		str = fmt.Sprint(str, "_", locale.Country)
	}
	if locale.Encoding != "" {
		str = fmt.Sprint(str, ".", locale.Encoding)
	}
	if locale.Modifier != "" {
		str = fmt.Sprint(str, "@", locale.Modifier)
	}
	return str
}

// Parse parses a formatted locale string and returns the corresponding Locale.
func Parse (value string) (Locale, error) {
	locale := Locale { }
	value, locale.Modifier, _ = strings.Cut(value, "@")
	value, locale.Encoding, _ = strings.Cut(value, ".")
	value, locale.Country,  _ = strings.Cut(value, "_")
	locale.Lang = value

	if hasIllegalRunes(locale.Lang) ||
		hasIllegalRunes(locale.Country) ||
		hasIllegalRunes(locale.Encoding) ||
		hasIllegalRunes(locale.Modifier) {
		
		return Locale { }, ErrUnexpectedRune
	}

	if locale.Lang == "" {
		return Locale { }, ErrLangEmpty
	}
	
	return locale, nil
}

func hasIllegalRunes (value string) bool {
	return strings.ContainsAny(value, "@._ ")
}