// Package geoflag maps server/profile names to ISO 3166-1 alpha-2 and emoji flags.
package geoflag

import (
	"regexp"
	"strings"
	"unicode"
)

var (
	reBracketCC = regexp.MustCompile(`(?i)[\[(]([a-z]{2})[\])]`)
	rePrefixCC  = regexp.MustCompile(`(?i)^([a-z]{2})(?:\s*[-_|/]\s*|\s+)`)
	reTokenCC   = regexp.MustCompile(`(?i)(?:^|[^a-z])([a-z]{2})(?:\s*[-_|]|$)`)
	reEmojiFlag = regexp.MustCompile(`[\x{1F1E6}-\x{1F1FF}]{2}`)
)

// FromText returns ISO2 (upper) and emoji flag, or empty if unknown.
func FromText(name string) (iso2, emoji string) {
	name = strings.TrimSpace(name)
	if name == "" {
		return "", ""
	}
	if m := reEmojiFlag.FindString(name); m != "" {
		if cc := emojiToISO(m); cc != "" {
			return cc, m
		}
	}
	lower := strings.ToLower(name)
	for _, pair := range countryNames {
		if strings.Contains(lower, pair.name) {
			return pair.code, ISOToEmoji(pair.code)
		}
	}
	if m := reBracketCC.FindStringSubmatch(name); len(m) == 2 {
		cc := strings.ToUpper(m[1])
		if Known(cc) {
			return cc, ISOToEmoji(cc)
		}
	}
	if m := rePrefixCC.FindStringSubmatch(name); len(m) == 2 {
		cc := strings.ToUpper(m[1])
		if Known(cc) {
			return cc, ISOToEmoji(cc)
		}
	}
	if m := reTokenCC.FindStringSubmatch(name); len(m) == 2 {
		cc := strings.ToUpper(m[1])
		if Known(cc) {
			return cc, ISOToEmoji(cc)
		}
	}
	return "", ""
}

// Known reports whether cc is a mapped ISO2 code.
func Known(cc string) bool {
	cc = strings.ToUpper(strings.TrimSpace(cc))
	_, ok := isoSet[cc]
	return ok
}

// ISOToEmoji converts "DE" → "🇩🇪". Invalid → "".
func ISOToEmoji(cc string) string {
	cc = strings.ToUpper(strings.TrimSpace(cc))
	if len(cc) != 2 {
		return ""
	}
	a, b := rune(cc[0]), rune(cc[1])
	if a < 'A' || a > 'Z' || b < 'A' || b > 'Z' {
		return ""
	}
	return string(rune(0x1F1E6+a-'A')) + string(rune(0x1F1E6+b-'A'))
}

func emojiToISO(flag string) string {
	rs := []rune(flag)
	if len(rs) != 2 {
		return ""
	}
	a, b := rs[0]-0x1F1E6, rs[1]-0x1F1E6
	if a < 0 || a > 25 || b < 0 || b > 25 {
		return ""
	}
	cc := string([]byte{byte('A' + a), byte('A' + b)})
	if !Known(cc) {
		// Still return regional indicator pair as ISO guess for display.
		if unicode.IsLetter(rune('A'+a)) {
			return cc
		}
		return ""
	}
	return cc
}

type nameCode struct {
	name string
	code string
}

// Longer / more specific names first where needed.
var countryNames = []nameCode{
	{"netherlands", "NL"}, {"deutschland", "DE"}, {"germany", "DE"},
	{"united kingdom", "GB"}, {"great britain", "GB"}, {"england", "GB"},
	{"united states", "US"}, {"america", "US"}, {"finland", "FI"},
	{"sweden", "SE"}, {"norway", "NO"}, {"denmark", "DK"}, {"poland", "PL"},
	{"france", "FR"}, {"spain", "ES"}, {"italy", "IT"}, {"portugal", "PT"},
	{"switzerland", "CH"}, {"austria", "AT"}, {"belgium", "BE"},
	{"czech", "CZ"}, {"slovakia", "SK"}, {"hungary", "HU"}, {"romania", "RO"},
	{"bulgaria", "BG"}, {"ukraine", "UA"}, {"russia", "RU"}, {"turkey", "TR"},
	{"israel", "IL"}, {"uae", "AE"}, {"emirates", "AE"}, {"dubai", "AE"},
	{"singapore", "SG"}, {"hong kong", "HK"}, {"japan", "JP"}, {"korea", "KR"},
	{"taiwan", "TW"}, {"india", "IN"}, {"canada", "CA"}, {"mexico", "MX"},
	{"brazil", "BR"}, {"argentina", "AR"}, {"australia", "AU"},
	{"new zealand", "NZ"}, {"latvia", "LV"}, {"lithuania", "LT"},
	{"estonia", "EE"}, {"moldova", "MD"}, {"georgia", "GE"}, {"armenia", "AM"},
	{"kazakhstan", "KZ"}, {"uzbekistan", "UZ"}, {"serbia", "RS"},
	{"croatia", "HR"}, {"slovenia", "SI"}, {"greece", "GR"}, {"cyprus", "CY"},
	{"ireland", "IE"}, {"iceland", "IS"}, {"luxembourg", "LU"},
	{"malaysia", "MY"}, {"thailand", "TH"}, {"vietnam", "VN"},
	{"indonesia", "ID"}, {"philippines", "PH"}, {"south africa", "ZA"},
}

var isoSet = map[string]struct{}{
	"AD": {}, "AE": {}, "AF": {}, "AL": {}, "AM": {}, "AR": {}, "AT": {}, "AU": {},
	"AZ": {}, "BA": {}, "BD": {}, "BE": {}, "BG": {}, "BH": {}, "BR": {}, "BY": {},
	"CA": {}, "CH": {}, "CL": {}, "CN": {}, "CO": {}, "CY": {}, "CZ": {}, "DE": {},
	"DK": {}, "EE": {}, "EG": {}, "ES": {}, "FI": {}, "FR": {}, "GB": {}, "GE": {},
	"GR": {}, "HK": {}, "HR": {}, "HU": {}, "ID": {}, "IE": {}, "IL": {}, "IN": {},
	"IQ": {}, "IR": {}, "IS": {}, "IT": {}, "JP": {}, "KG": {}, "KR": {}, "KZ": {},
	"LT": {}, "LU": {}, "LV": {}, "MD": {}, "MK": {}, "MX": {}, "MY": {}, "NL": {},
	"NO": {}, "NZ": {}, "PH": {}, "PK": {}, "PL": {}, "PT": {}, "RO": {}, "RS": {},
	"RU": {}, "SA": {}, "SE": {}, "SG": {}, "SI": {}, "SK": {}, "TH": {}, "TJ": {},
	"TM": {}, "TR": {}, "TW": {}, "UA": {}, "US": {}, "UZ": {}, "VN": {}, "ZA": {},
}