package protocol

// isISO3166Alpha2 reports whether code is a valid ISO 3166-1 alpha-2 country code.
// Officially-assigned codes and user-assigned codes (AA, QM–QZ, XA–XZ, ZZ) are both
// accepted; the W3C WebAuthn test vectors use AA, so rejecting user-assigned codes
// would fail §16 conformance. Codes of the wrong length, wrong case, or containing
// non-letters are rejected.
func isISO3166Alpha2(code string) bool {
	if _, ok := iso3166Alpha2Codes[code]; ok {
		return true
	}

	return isISO3166Alpha2UserAssigned(code)
}

// isISO3166Alpha2UserAssigned reports whether code is a user-assignable code per
// ISO 3166-1 (AA, QM–QZ, XA–XZ, ZZ).
func isISO3166Alpha2UserAssigned(code string) bool {
	if len(code) != 2 {
		return false
	}

	switch code {
	case "AA", "ZZ":
		return true
	}

	switch code[0] {
	case 'Q':
		return code[1] >= 'M' && code[1] <= 'Z'
	case 'X':
		return code[1] >= 'A' && code[1] <= 'Z'
	}

	return false
}

var iso3166Alpha2Codes = map[string]struct{}{
	"AD": {}, "AE": {}, "AF": {}, "AG": {}, "AI": {}, "AL": {}, "AM": {}, "AO": {},
	"AQ": {}, "AR": {}, "AS": {}, "AT": {}, "AU": {}, "AW": {}, "AX": {}, "AZ": {},
	"BA": {}, "BB": {}, "BD": {}, "BE": {}, "BF": {}, "BG": {}, "BH": {}, "BI": {},
	"BJ": {}, "BL": {}, "BM": {}, "BN": {}, "BO": {}, "BQ": {}, "BR": {}, "BS": {},
	"BT": {}, "BV": {}, "BW": {}, "BY": {}, "BZ": {},
	"CA": {}, "CC": {}, "CD": {}, "CF": {}, "CG": {}, "CH": {}, "CI": {}, "CK": {},
	"CL": {}, "CM": {}, "CN": {}, "CO": {}, "CR": {}, "CU": {}, "CV": {}, "CW": {},
	"CX": {}, "CY": {}, "CZ": {},
	"DE": {}, "DJ": {}, "DK": {}, "DM": {}, "DO": {}, "DZ": {},
	"EC": {}, "EE": {}, "EG": {}, "EH": {}, "ER": {}, "ES": {}, "ET": {},
	"FI": {}, "FJ": {}, "FK": {}, "FM": {}, "FO": {}, "FR": {},
	"GA": {}, "GB": {}, "GD": {}, "GE": {}, "GF": {}, "GG": {}, "GH": {}, "GI": {},
	"GL": {}, "GM": {}, "GN": {}, "GP": {}, "GQ": {}, "GR": {}, "GS": {}, "GT": {},
	"GU": {}, "GW": {}, "GY": {},
	"HK": {}, "HM": {}, "HN": {}, "HR": {}, "HT": {}, "HU": {},
	"ID": {}, "IE": {}, "IL": {}, "IM": {}, "IN": {}, "IO": {}, "IQ": {}, "IR": {},
	"IS": {}, "IT": {},
	"JE": {}, "JM": {}, "JO": {}, "JP": {},
	"KE": {}, "KG": {}, "KH": {}, "KI": {}, "KM": {}, "KN": {}, "KP": {}, "KR": {},
	"KW": {}, "KY": {}, "KZ": {},
	"LA": {}, "LB": {}, "LC": {}, "LI": {}, "LK": {}, "LR": {}, "LS": {}, "LT": {},
	"LU": {}, "LV": {}, "LY": {},
	"MA": {}, "MC": {}, "MD": {}, "ME": {}, "MF": {}, "MG": {}, "MH": {}, "MK": {},
	"ML": {}, "MM": {}, "MN": {}, "MO": {}, "MP": {}, "MQ": {}, "MR": {}, "MS": {},
	"MT": {}, "MU": {}, "MV": {}, "MW": {}, "MX": {}, "MY": {}, "MZ": {},
	"NA": {}, "NC": {}, "NE": {}, "NF": {}, "NG": {}, "NI": {}, "NL": {}, "NO": {},
	"NP": {}, "NR": {}, "NU": {}, "NZ": {},
	"OM": {},
	"PA": {}, "PE": {}, "PF": {}, "PG": {}, "PH": {}, "PK": {}, "PL": {}, "PM": {},
	"PN": {}, "PR": {}, "PS": {}, "PT": {}, "PW": {}, "PY": {},
	"QA": {},
	"RE": {}, "RO": {}, "RS": {}, "RU": {}, "RW": {},
	"SA": {}, "SB": {}, "SC": {}, "SD": {}, "SE": {}, "SG": {}, "SH": {}, "SI": {},
	"SJ": {}, "SK": {}, "SL": {}, "SM": {}, "SN": {}, "SO": {}, "SR": {}, "SS": {},
	"ST": {}, "SV": {}, "SX": {}, "SY": {}, "SZ": {},
	"TC": {}, "TD": {}, "TF": {}, "TG": {}, "TH": {}, "TJ": {}, "TK": {}, "TL": {},
	"TM": {}, "TN": {}, "TO": {}, "TR": {}, "TT": {}, "TV": {}, "TW": {}, "TZ": {},
	"UA": {}, "UG": {}, "UM": {}, "US": {}, "UY": {}, "UZ": {},
	"VA": {}, "VC": {}, "VE": {}, "VG": {}, "VI": {}, "VN": {}, "VU": {},
	"WF": {}, "WS": {},
	"YE": {}, "YT": {},
	"ZA": {}, "ZM": {}, "ZW": {},
}