IPアドレス判定

export class CIDR {
  #cidr: string;
  #baseIp: number;
  #subnet: number;

  constructor(cidr: string) {
    this.#cidr = cidr;
    const [baseIp, mask] = cidr.split("/");
    this.#baseIp = this.#ipToLong(baseIp);
    this.#subnet = this.#cidrToSubnet(Number.parseInt(mask, 10));
  }

  get cidr() {
    return this.#cidr;
  }

  isInCidrRange(ip: string): boolean {
    const ipLong = this.#ipToLong(ip);
    const subnet = this.#subnet;
    return (ipLong & subnet) === (this.#baseIp & subnet);
  }

  getCidrRange(): string[] {
    const subnet = this.#subnet;
    const startIp = this.#baseIp & subnet;
    const endIp = startIp + (~subnet >>> 0);

    const ips: string[] = [];
    for (let i = startIp; i <= endIp; i++) {
      ips.push(this.#longToIp(i));
    }
    return ips;
  }

  #ipToLong(ip: string): number {
    return (
      ip
        .split(".")
        .reduce((acc, octet) => (acc << 8) + Number.parseInt(octet, 10), 0) >>>
      0
    );
  }

  #longToIp(long: number): string {
    const max = 255;
    return [
      (long >>> 24) & max,
      (long >>> 16) & max,
      (long >>> 8) & max,
      long & max,
    ].join(".");
  }

  #cidrToSubnet(cidr: number): number {
    return (-1 << (32 - cidr)) >>> 0;
  }
}