package util

import (
	"regexp"
	"strings"
)

// Flag detection rules: [regex, emoji].
// Per review-resolution #16: Go RE2 supports \p{Regional_Indicator} and \uFE0F.
var flagRules []flagRule

type flagRule struct {
	re    *regexp.Regexp
	emoji string
}

func init() {
	rules := []struct {
		pattern string
		emoji   string
	}{
		{`香港|港|hong\s*kong|\bhk\b`, "🇭🇰"},
		{`台湾|台灣|taiwan|\btw\b`, "🇹🇼"},
		{`新加坡|狮城|獅城|singapore|\bsg\b`, "🇸🇬"},
		{`日本|东京|東京|大阪|japan|tokyo|osaka|\bjp\b`, "🇯🇵"},
		{`美国|美國|洛杉矶|洛杉磯|纽约|紐約|united\s*states|los\s*angeles|new\s*york|\bus\b|\busa\b`, "🇺🇸"},
		{`英国|英國|伦敦|倫敦|united\s*kingdom|london|\buk\b`, "🇬🇧"},
		{`德国|德國|法兰克福|法蘭克福|germany|frankfurt|\bde\b`, "🇩🇪"},
		{`韩国|韓國|首尔|首爾|korea|seoul|\bkr\b`, "🇰🇷"},
	}
	for _, r := range rules {
		re, err := regexp.Compile("(?i)" + r.pattern)
		if err != nil {
			continue
		}
		flagRules = append(flagRules, flagRule{re: re, emoji: r.emoji})
	}
}

// DetectFlag returns the flag emoji for a name, or 🏳️ if no match.
func DetectFlag(name string) string {
	text := strings.ToLower(name)
	for _, rule := range flagRules {
		if rule.re.MatchString(text) {
			return rule.emoji
		}
	}
	return "🏳️"
}

// removeFlagRe matches leading flag emoji sequences and whitespace.
// Regional Indicator letters are U+1F1E6–U+1F1FF; ZWJ is U+200D; VS16 is U+FE0F.
var removeFlagRe = regexp.MustCompile(`^[\x{1F1E6}-\x{1F1FF}\x{FE0F}\x{200D}\s]+`)

// RemoveFlag strips leading flag emoji and whitespace from a name.
// Per review-resolution #16: handles ZWJ (\u200D) and variation selector (\uFE0F).
func RemoveFlag(name string) string {
	cleaned := removeFlagRe.ReplaceAllString(name, "")
	// Also strip leading 🏳️
	cleaned = strings.TrimLeft(cleaned, "🏳️ ")
	return strings.TrimSpace(cleaned)
}

// NormalizeTaiwanFlag maps the Taiwan flag to different flags based on `tw` mode.
// Per review-resolution #19: three modes — ws/tw/default.
func NormalizeTaiwanFlag(flag, mode string) string {
	if flag != "🇹🇼" {
		return flag
	}
	switch mode {
	case "ws":
		return "🇼🇸"
	case "tw":
		return "🇹🇼"
	default:
		return "🇨🇳"
	}
}

// IsASCII checks if a string contains only ASCII characters.
func IsASCII(s string) bool {
	for i := 0; i < len(s); i++ {
		if s[i] > 127 {
			return false
		}
	}
	return true
}