package whois

import (
	"bytes"
	"strings"
	"unicode"
	"unicode/utf8"

	"golang.org/x/text/encoding"
	"golang.org/x/text/encoding/simplifiedchinese"
	"golang.org/x/text/encoding/traditionalchinese"
)

func decodeWhoisPayload(raw []byte) (string, string) {
	trimmed := bytes.Trim(raw, "\x00")
	if len(trimmed) == 0 {
		return "", "unknown"
	}

	if bytes.HasPrefix(trimmed, []byte{0xEF, 0xBB, 0xBF}) {
		trimmed = trimmed[3:]
	}
	if utf8.Valid(trimmed) {
		return string(trimmed), "utf-8"
	}

	type candidate struct {
		name string
		enc  encoding.Encoding
	}
	candidates := []candidate{
		{name: "gb18030", enc: simplifiedchinese.GB18030},
		{name: "gbk", enc: simplifiedchinese.GBK},
		{name: "big5", enc: traditionalchinese.Big5},
	}

	bestText := string(trimmed)
	bestName := "binary"
	bestScore := -1 << 30

	for _, c := range candidates {
		decoded, err := c.enc.NewDecoder().Bytes(trimmed)
		if err != nil {
			continue
		}
		text := string(decoded)
		score := scoreDecodedText(text)
		if score > bestScore {
			bestScore = score
			bestText = text
			bestName = c.name
		}
	}
	return bestText, bestName
}

func scoreDecodedText(s string) int {
	if strings.TrimSpace(s) == "" {
		return -10000
	}

	score := 0
	for _, r := range s {
		switch {
		case r == utf8.RuneError:
			score -= 80
		case r == '\n' || r == '\r' || r == '\t':
			score += 2
		case unicode.IsLetter(r) || unicode.IsDigit(r):
			score += 3
		case unicode.IsPrint(r):
			score += 1
		default:
			score -= 2
		}
	}
	return score
}