/**
 * IP Range utility functions for network scanning
 */

/**
 * Validates an IPv4 address
 */
export function isValidIp(ip: string): boolean {
  const parts = ip.split('.');
  if (parts.length !== 4) return false;

  return parts.every((part) => {
    const num = parseInt(part, 10);
    return !isNaN(num) && num >= 0 && num <= 255 && part === num.toString();
  });
}

/**
 * Converts an IPv4 address to a 32-bit number
 */
export function ipToNumber(ip: string): number {
  const parts = ip.split('.').map((p) => parseInt(p, 10));
  return ((parts[0] << 24) | (parts[1] << 16) | (parts[2] << 8) | parts[3]) >>> 0;
}

/**
 * Converts a 32-bit number to an IPv4 address
 */
export function numberToIp(num: number): string {
  return [
    (num >>> 24) & 255,
    (num >>> 16) & 255,
    (num >>> 8) & 255,
    num & 255,
  ].join('.');
}

/**
 * Generates an array of IP addresses from a start to end range
 * Excludes network address (.0) and broadcast address (.255) for /24 ranges
 */
export function ipRangeToIps(startIp: string, endIp: string): string[] {
  if (!isValidIp(startIp) || !isValidIp(endIp)) {
    throw new Error(`Invalid IP address: ${!isValidIp(startIp) ? startIp : endIp}`);
  }

  const start = ipToNumber(startIp);
  const end = ipToNumber(endIp);

  if (start > end) {
    throw new Error(`Start IP (${startIp}) must be less than or equal to end IP (${endIp})`);
  }

  const ips: string[] = [];
  for (let i = start; i <= end; i++) {
    ips.push(numberToIp(i));
  }

  return ips;
}

/**
 * Parses CIDR notation and returns an array of usable host IPs
 * Excludes network address and broadcast address
 * Example: "192.168.1.0/24" returns 192.168.1.1 through 192.168.1.254
 */
export function cidrToIps(cidr: string): string[] {
  const match = cidr.match(/^(\d+\.\d+\.\d+\.\d+)\/(\d+)$/);
  if (!match) {
    throw new Error(`Invalid CIDR notation: ${cidr}`);
  }

  const [, networkIp, prefixStr] = match;
  const prefix = parseInt(prefixStr, 10);

  if (!isValidIp(networkIp)) {
    throw new Error(`Invalid network address: ${networkIp}`);
  }

  if (prefix < 0 || prefix > 32) {
    throw new Error(`Invalid prefix length: ${prefix}`);
  }

  // For /32, just return the single IP
  if (prefix === 32) {
    return [networkIp];
  }

  // For /31 (point-to-point), return both IPs
  if (prefix === 31) {
    const networkNum = ipToNumber(networkIp);
    const mask = (0xffffffff << (32 - prefix)) >>> 0;
    const network = (networkNum & mask) >>> 0;
    return [numberToIp(network), numberToIp(network + 1)];
  }

  // Calculate network and broadcast addresses
  const networkNum = ipToNumber(networkIp);
  const mask = (0xffffffff << (32 - prefix)) >>> 0;
  const network = (networkNum & mask) >>> 0;
  const broadcast = (network | (~mask >>> 0)) >>> 0;

  // Generate usable host IPs (exclude network and broadcast)
  const ips: string[] = [];
  for (let i = network + 1; i < broadcast; i++) {
    ips.push(numberToIp(i));
  }

  return ips;
}

/**
 * Gets the local network interfaces and returns the first non-loopback IPv4 subnet
 * Returns CIDR notation (e.g., "192.168.1.0/24")
 */
export function getLocalSubnet(): string | null {
  try {
    const os = require('os');
    const interfaces = os.networkInterfaces();

    for (const name of Object.keys(interfaces)) {
      const iface = interfaces[name];
      if (!iface) continue;

      for (const info of iface) {
        // Skip loopback and non-IPv4
        if (info.family !== 'IPv4' || info.internal) continue;

        // Calculate the network address from IP and netmask
        const ip = ipToNumber(info.address);
        const mask = ipToNumber(info.netmask);
        const network = (ip & mask) >>> 0;

        // Calculate prefix length from netmask
        const maskBits = info.netmask.split('.').reduce((acc: number, octet: string) => {
          const byte = parseInt(octet, 10);
          let bits = 0;
          for (let i = 7; i >= 0; i--) {
            if ((byte >> i) & 1) bits++;
            else break;
          }
          return acc + bits;
        }, 0);

        return `${numberToIp(network)}/${maskBits}`;
      }
    }
  } catch {
    // os module might not be available
  }

  return null;
}

/**
 * Counts the number of IPs in a CIDR range (excluding network and broadcast)
 */
export function countIpsInCidr(cidr: string): number {
  const match = cidr.match(/^(\d+\.\d+\.\d+\.\d+)\/(\d+)$/);
  if (!match) {
    throw new Error(`Invalid CIDR notation: ${cidr}`);
  }

  const prefix = parseInt(match[2], 10);

  if (prefix === 32) return 1;
  if (prefix === 31) return 2;

  // 2^(32-prefix) - 2 (minus network and broadcast)
  return Math.pow(2, 32 - prefix) - 2;
}