package core

import "strings"

// Five bytes per entry, alpha-3 then alpha-2, sorted by alpha-3.
const iso3166Packed = "ABWAWAFGAFAGOAOAIAAIALAAXALBALANDADAREAEARGARARMAMASMASATAAQ" +
	"ATFTFATGAGAUSAUAUTATAZEAZBDIBIBELBEBENBJBESBQBFABFBGDBDBGRBG" +
	"BHRBHBHSBSBIHBABLMBLBLRBYBLZBZBMUBMBOLBOBRABRBRBBBBRNBNBTNBT" +
	"BVTBVBWABWCAFCFCANCACCKCCCHECHCHLCLCHNCNCIVCICMRCMCODCDCOGCG" +
	"COKCKCOLCOCOMKMCPVCVCRICRCUBCUCUWCWCXRCXCYMKYCYPCYCZECZDEUDE" +
	"DJIDJDMADMDNKDKDOMDODZADZECUECEGYEGERIERESHEHESPESESTEEETHET" +
	"FINFIFJIFJFLKFKFRAFRFROFOFSMFMGABGAGBRGBGEOGEGGYGGGHAGHGIBGI" +
	"GINGNGLPGPGMBGMGNBGWGNQGQGRCGRGRDGDGRLGLGTMGTGUFGFGUMGUGUYGY" +
	"HKGHKHMDHMHNDHNHRVHRHTIHTHUNHUIDNIDIMNIMINDINIOTIOIRLIEIRNIR" +
	"IRQIQISLISISRILITAITJAMJMJEYJEJORJOJPNJPKAZKZKENKEKGZKGKHMKH" +
	"KIRKIKNAKNKORKRKWTKWLAOLALBNLBLBRLRLBYLYLCALCLIELILKALKLSOLS" +
	"LTULTLUXLULVALVMACMOMAFMFMARMAMCOMCMDAMDMDGMGMDVMVMEXMXMHLMH" +
	"MKDMKMLIMLMLTMTMMRMMMNEMEMNGMNMNPMPMOZMZMRTMRMSRMSMTQMQMUSMU" +
	"MWIMWMYSMYMYTYTNAMNANCLNCNERNENFKNFNGANGNICNINIUNUNLDNLNORNO" +
	"NPLNPNRUNRNZLNZOMNOMPAKPKPANPAPCNPNPERPEPHLPHPLWPWPNGPGPOLPL" +
	"PRIPRPRKKPPRTPTPRYPYPSEPSPYFPFQATQAREUREROURORUSRURWARWSAUSA" +
	"SDNSDSENSNSGPSGSGSGSSHNSHSJMSJSLBSBSLESLSLVSVSMRSMSOMSOSPMPM" +
	"SRBRSSSDSSSTPSTSURSRSVKSKSVNSISWESESWZSZSXMSXSYCSCSYRSYTCATC" +
	"TCDTDTGOTGTHATHTJKTJTKLTKTKMTMTLSTLTONTOTTOTTTUNTNTURTRTUVTV" +
	"TWNTWTZATZUGAUGUKRUAUMIUMURYUYUSAUSUZBUZVATVAVCTVCVENVEVGBVG" +
	"VIRVIVNMVNVUTVUWLFWFWSMWSYEMYEZAFZAZMBZMZWEZW"

// normalizeRegion folds a country code to the alpha-2 form Dart renders a flag
// from, or "" when it is not one. Only Gemini reports alpha-3.
func normalizeRegion(code string) string {
	code = strings.ToUpper(strings.TrimSpace(code))
	switch len(code) {
	case 2:
		if isAsciiUpper(code) {
			return code
		}
		return ""
	case 3:
		if !isAsciiUpper(code) {
			return ""
		}
		low, high := 0, len(iso3166Packed)/5
		for low < high {
			mid := (low + high) / 2
			entry := iso3166Packed[mid*5 : mid*5+3]
			switch {
			case entry < code:
				low = mid + 1
			case entry > code:
				high = mid
			default:
				return iso3166Packed[mid*5+3 : mid*5+5]
			}
		}
		return ""
	default:
		return ""
	}
}

func isAsciiUpper(value string) bool {
	for _, char := range value {
		if char < 'A' || char > 'Z' {
			return false
		}
	}
	return true
}