package stringencoding

import (
	"fmt"
	"io/ioutil"
	"strings"

	"github.com/axgle/mahonia"
	"golang.org/x/text/encoding"
	"golang.org/x/text/encoding/charmap"
	"golang.org/x/text/encoding/unicode"
	"golang.org/x/text/encoding/unicode/utf32"
	"golang.org/x/text/transform"
)

func DecodeString(encodingName string, input []byte) (string, error) {
	if encodingName == "" {
		return "", fmt.Errorf("empty encoding string")
	}

	if input == nil || len(input) == 0 {
		return "", fmt.Errorf("empty or null input")
	}

	var decoder *encoding.Decoder

	// Определяем декодер в зависимости от кодировки
	switch strings.ToLower(encodingName) {
	case "utf-8":
		decoder = unicode.UTF8.NewDecoder()
	case "utf-16":
		decoder = unicode.UTF16(unicode.LittleEndian, unicode.UseBOM).NewDecoder()
	case "utf-16be":
		decoder = unicode.UTF16(unicode.BigEndian, unicode.UseBOM).NewDecoder()
	case "utf-32":
		decoder = utf32.UTF32(utf32.LittleEndian, utf32.UseBOM).NewDecoder()
	case "utf-32be":
		decoder = utf32.UTF32(utf32.BigEndian, utf32.UseBOM).NewDecoder()
	case "windows-1252":
		decoder = charmap.Windows1252.NewDecoder()
	case "iso-8859-1":
		decoder = charmap.ISO8859_1.NewDecoder()
	case "iso-8859-2":
		decoder = charmap.ISO8859_2.NewDecoder()
	case "iso-8859-3":
		decoder = charmap.ISO8859_3.NewDecoder()
	case "iso-8859-4":
		decoder = charmap.ISO8859_4.NewDecoder()
	case "iso-8859-5":
		decoder = charmap.ISO8859_5.NewDecoder()
	case "iso-8859-6":
		decoder = charmap.ISO8859_6.NewDecoder()
	case "iso-8859-7":
		decoder = charmap.ISO8859_7.NewDecoder()
	case "iso-8859-8":
		decoder = charmap.ISO8859_8.NewDecoder()
	case "iso-8859-9":
		decoder = charmap.ISO8859_9.NewDecoder()
	case "koi8-r":
		decoder = charmap.KOI8R.NewDecoder()
	case "gb2312":
		return decodeGB2312(input)
	case "gbk":
		return decodeGBK(input)
	case "shift_jis":
		return decodeShiftJIS(input)
	case "euc-jp":
		return decodeEUCJP(input)
	default:
		return "", fmt.Errorf("unsupported encoding: %s", encodingName)
	}

	// Декодируем входные байты
	decodingReader := transform.NewReader(strings.NewReader(string(input)), decoder)
	decodedBytes, err := ioutil.ReadAll(decodingReader)
	if err != nil {
		return "", err
	}

	return string(decodedBytes), nil
}

// Функции для декодирования специфических кодировок с использованием mahonia
func decodeGB2312(input []byte) (string, error) {
	decoder := mahonia.NewDecoder("gb2312")
	return decoder.ConvertString(string(input)), nil
}

func decodeGBK(input []byte) (string, error) {
	decoder := mahonia.NewDecoder("gbk")
	return decoder.ConvertString(string(input)), nil
}

func decodeShiftJIS(input []byte) (string, error) {
	decoder := mahonia.NewDecoder("shift_jis")
	return decoder.ConvertString(string(input)), nil
}

func decodeEUCJP(input []byte) (string, error) {
	decoder := mahonia.NewDecoder("euc-jp")
	return decoder.ConvertString(string(input)), nil
}