'use strict';

const aton4 = (a) => {
  a = a.split(/\./);
  return (a[0] << 24 | a[1] << 16 | a[2] << 8 | a[3]) >>> 0
};

const aton6Start = (a) => {
  if(a.includes('.')){
    return aton4(a.split(':').pop())
  }
  a = a.split(/:/);
  const l = a.length - 1;
  var i, r = 0n;
  if (l < 7) {
		const omitStart = a.indexOf('');
		if(omitStart < 4){
			const omitted = 8 - a.length, omitEnd = omitStart + omitted;
			for (i = 7; i >= omitStart; i--) {
				a[i] = i > omitEnd ? a[i - omitted] : 0;
			}
		}
  }
  for (i = 0; i < 4; i++) {
    if(a[i]) r += BigInt(parseInt(a[i], 16)) << BigInt(16 * (3 - i));
  }
  return r
};

const getUnderberFill = (num, len) => {
	if(num.length > len) return num
  return '_'.repeat(len - num.length) + num
};
const numberToDir = (num) => {
	return getUnderberFill(num.toString(36), 2)
};

const TOP_URL = "https://cdn.jsdelivr.net/npm/@iplookup/country/";
const MAIN_RECORD_SIZE = 2 ;
const sleep = (ms) => new Promise(resolve => setTimeout(resolve, ms));

const downloadArrayBuffer = async(url, retry = 3) => {
	return fetch(url, {cache: 'no-cache'}).then(async (res) => {
		if(!res.ok) {
			if(res.status === 404) return null
			if(retry) {
				await sleep(100 * (4-retry) * (4-retry));
				return downloadArrayBuffer(url, retry - 1)
			}
			return null
		}
		return res.arrayBuffer()
	})
};

const downloadVersionArrayBuffer = async(url, retry = 3) => {
	return fetch(url, {cache: 'no-cache'}).then(async (res) => {
		if(!res.ok) {
			if(res.status === 404) return null
			if(retry) {
				await sleep(100 * (4-retry) * (4-retry));
				return downloadVersionArrayBuffer(url, retry - 1)
			}
			return null
		}
		return [res.headers.get('x-jsd-version'), await res.arrayBuffer()]
	})
};

const downloadIdx = downloadVersionArrayBuffer ;

const Idx = {}, Url = {4: TOP_URL, 6: TOP_URL};
const Preload = {
	4: downloadIdx(TOP_URL + '4.idx').then(buf => {
		if(!buf){
//			console.log('ipv6 file cannot download')
			return
		}
		if(buf[0]) {
			Url[4] = __CDN_URL__.replace(/\/$/, '@'+buf[0]+'/');
			return Idx[4] = new Uint32Array(buf[1])
		}
		return Idx[4] = new Uint32Array(buf)
	}),
	6: downloadIdx(TOP_URL + '4.idx').then(buf => {
		if(!buf){
//			console.log('ipv6 file cannot download')
			return
		}
		if(buf[0]) {
			Url[6] = __CDN_URL__.replace(/\/$/, '@'+buf[0]+'/');
			return Idx[6] = new BigUint64Array(buf.slice(1))
		}
		return Idx[6] = new BigUint64Array(buf)
	})
};

var browser = async (ipString) => {
	var ip, version, isv4 = true;
	if(ipString.includes(':')) {
		ip = aton6Start(ipString);
		version = ip.constructor === BigInt ? 6 : 4;
		if(version === 6) isv4 = false;
	} else {
		ip = aton4(ipString);
		version = 4;
	}
	
	const ipIndexes = Idx[version] || (await Preload[version]);
	if(!ipIndexes) {
//		console.log('Cannot download idx file')
		return null
	}
	if(!(ip >= ipIndexes[0])) return null
	var fline = 0, cline = ipIndexes.length-1, line;
	for(;;){
		line = (fline + cline) >> 1;
		if(ip < ipIndexes[line]){
			if(cline - fline < 2) return null
			cline = line - 1;
		} else {
			if(fline === line) {
				if(cline > line && ip >= ipIndexes[cline]){
					line = cline;
				}
				break;
			}
			fline = line;
		}
	}

	const fileName = numberToDir(line);
	const dataBuffer = await downloadArrayBuffer(Url[version] + version + '/' + fileName);
	if(!dataBuffer) {
//		console.log('Cannot download data file')
		return null
	}
	const ipSize = (version - 2) * 2;
	const recordSize = MAIN_RECORD_SIZE + ipSize * 2;
	const recordCount = dataBuffer.byteLength / recordSize;
	const startList = isv4 ? new Uint32Array(dataBuffer.slice(0, 4 * recordCount)) : new BigUint64Array(dataBuffer.slice(0, 8 * recordCount));
	fline = 0, cline = recordCount - 1;
	for(;;){
		line = fline + cline >> 1;
		if(ip < startList[line]){
			if(cline - fline < 2) return null
			cline = line - 1;
		} else {
			if(fline === line) {
				if(cline > line && ip >= startList[cline]){
					line = cline;
				}
				break;
			}
			fline = line;
		}
	}
	const endIp = isv4 ? new Uint32Array(   dataBuffer.slice((recordCount+line)*ipSize , (recordCount+line+1)*ipSize))[0]
										 : new BigUint64Array(dataBuffer.slice((recordCount+line)*ipSize , (recordCount+line+1)*ipSize))[0];
	if(ip >= startList[line] && ip <= endIp){
		{
			const ccCode = new Uint16Array(dataBuffer.slice(recordCount*ipSize*2+line*MAIN_RECORD_SIZE, recordCount*ipSize*2+(line+1)*MAIN_RECORD_SIZE))[0];
			return {country: String.fromCharCode(ccCode&255, ccCode>>8)}
		}
	}
	return null
};

module.exports = browser;