const XOR_CODE = 23442827791579n;
const MASK_CODE = 2251799813685247n;
const MAX_AID = 1n << 51n;
const BASE = 58n;

const data = "FcwAPNKTMug3GV5Lj7EJnHpWsx4tb8haYeviqBz6rkCy12mUSDQX9RdoZf";

export function av2bv(aid: number) {
	const bytes = ["B", "V", "1", "0", "0", "0", "0", "0", "0", "0", "0", "0"];
	let bvIndex = bytes.length - 1;
	let tmp = (MAX_AID | BigInt(aid)) ^ XOR_CODE;
	while (tmp > 0) {
		bytes[bvIndex] = data[Number(tmp % BigInt(BASE))];
		tmp = tmp / BASE;
		bvIndex -= 1;
	}
	[bytes[3], bytes[9]] = [bytes[9], bytes[3]];
	[bytes[4], bytes[7]] = [bytes[7], bytes[4]];
	return bytes.join("") as `BV1${string}`;
}

export function bv2av(bvid: `BV1${string}`) {
	const bvidArr = Array.from<string>(bvid);
	[bvidArr[3], bvidArr[9]] = [bvidArr[9], bvidArr[3]];
	[bvidArr[4], bvidArr[7]] = [bvidArr[7], bvidArr[4]];
	bvidArr.splice(0, 3);
	const tmp = bvidArr.reduce((pre, bvidChar) => pre * BASE + BigInt(data.indexOf(bvidChar)), 0n);
	return Number((tmp & MASK_CODE) ^ XOR_CODE);
}
