// Ported from filius-ipad (GPLv2/GPLv3):
//   State/TopologyNetworkRuntimeEngine.swift (parseIPv4, sameSubnet)
//   State/TopologyEditorState.swift (TopologyRuntimeManualRoute.parseIPv4)
//
// Two parsers exist on purpose, as in the Swift source: the runtime reads an
// octet the way Swift's `UInt8(String)` does, the route editor the way Java
// FILIUS validates its table cells (see routeTable.ts).

/**
 * Swift `UInt8(segment)`: an optional sign, then decimal digits, value 0…255.
 * Leading zeros are allowed ("007" is 7), whitespace is not.
 */
function parseSwiftOctet(segment: string): number | undefined {
  if (!/^[+-]?[0-9]+$/.test(segment)) return undefined;
  const value = Number(segment);
  if (!Number.isInteger(value) || value < 0 || value > 255) return undefined;
  return Object.is(value, -0) ? 0 : value;
}

/** Dotted quad to an unsigned 32-bit number, or undefined. */
export function parseIPv4(value: string): number | undefined {
  const segments = value.split('.');
  if (segments.length !== 4) return undefined;
  let address = 0;
  for (const segment of segments) {
    const octet = parseSwiftOctet(segment);
    if (octet === undefined) return undefined;
    address = ((address << 8) | octet) >>> 0;
  }
  return address;
}

export function formatIPv4(address: number): string {
  return [24, 16, 8, 0].map((shift) => String((address >>> shift) & 0xff)).join('.');
}

export function sameSubnet(lhs: string, rhs: string, mask: string): boolean {
  const left = parseIPv4(lhs);
  const right = parseIPv4(rhs);
  const netmask = parseIPv4(mask);
  if (left === undefined || right === undefined || netmask === undefined) return false;
  return ((left & netmask) >>> 0) === ((right & netmask) >>> 0);
}

/** `address & mask` as an unsigned number. */
export function maskAddress(address: number, mask: number): number {
  return (address & mask) >>> 0;
}