// Ported from filius-ipad (GPLv2/GPLv3):
//   State/TopologyJavaRouteTable.swift (row projection, validation, drafts)
// Java counterpart: filius.software.vermittlungsschicht.Weiterleitungstabelle
//   (holeTabelle: the order of the generated rows).
// The Swift file also carries table geometry for SwiftUI; that belongs to the
// editor and is not ported here.

import { formatIPv4, maskAddress } from './ipv4.js';
import type { InterfaceConfiguration, ManualRoute } from './config.js';

export type RouteOrigin = 'localHost' | 'connected' | 'localhost' | 'manual' | 'defaultGateway' | 'rip';

export interface RouteRow {
  readonly destinationNetwork: string;
  readonly subnetMask: string;
  readonly nextHop: string;
  readonly interfaceIPAddress: string;
  readonly origin: RouteOrigin;
  readonly isEditable: boolean;
  readonly metric?: number;
  readonly expiresAtMilliseconds?: number;
  /** A RIP route: the router that told it, by its first address (Java's hopPublicIp, a hint for the administrator). */
  readonly hopPublicIPAddress?: string;
}

export type RouteTableColumn = 'destination' | 'subnetMask' | 'nextGateway' | 'interface';

/**
 * A Java table octet: digits only, leading zeros allowed, at most three
 * significant digits, 0…255 ("001" is valid, " 1" and "+1" are not).
 */
function parseJavaOctet(segment: string): number | undefined {
  if (segment.length === 0 || !/^[0-9]+$/.test(segment)) return undefined;
  const significant = segment.replace(/^0+/, '');
  if (significant.length === 0) return 0;
  if (significant.length > 3) return undefined;
  const value = Number(significant);
  return value <= 255 ? value : undefined;
}

function parseJavaIPv4(value: string): number | undefined {
  const segments = value.split('.');
  if (segments.length !== 4) return undefined;
  let address = 0;
  for (const segment of segments) {
    const octet = parseJavaOctet(segment);
    if (octet === undefined) return undefined;
    address = ((address << 8) | octet) >>> 0;
  }
  return address;
}

export function isValidJavaIPAddress(value: string): boolean {
  return parseJavaIPv4(value) !== undefined;
}

/**
 * FILIUS uses `musterSubNetz`, a dotted-decimal syntax check. It deliberately
 * accepts non-contiguous masks in the route editor.
 */
export function isValidJavaSubnetMask(value: string): boolean {
  return parseJavaIPv4(value) !== undefined;
}

export function isValidRouteCell(value: string, column: RouteTableColumn): boolean {
  return column === 'subnetMask' ? isValidJavaSubnetMask(value) : isValidJavaIPAddress(value);
}

function sameNetwork(lhs: string, rhs: string, mask: string): boolean {
  const left = parseJavaIPv4(lhs);
  const right = parseJavaIPv4(rhs);
  const netmask = parseJavaIPv4(mask);
  if (left === undefined || right === undefined || netmask === undefined) return false;
  return maskAddress(left, netmask) === maskAddress(right, netmask);
}

function networkAddress(ipAddress: string, subnetMask: string): string | undefined {
  const address = parseJavaIPv4(ipAddress);
  const mask = parseJavaIPv4(subnetMask);
  if (address === undefined || mask === undefined) return undefined;
  return formatIPv4(maskAddress(address, mask));
}

/**
 * The static table as Java shows it: the interfaces' own addresses (newest
 * first), their networks, loopback, the manual rows, then the default route.
 */
export function routeTableRows(
  interfaceConfigurations: readonly InterfaceConfiguration[],
  manualRoutes: readonly ManualRoute[],
  defaultGateway: string | undefined,
): RouteRow[] {
  const validInterfaces = interfaceConfigurations.filter(
    (configuration) =>
      parseJavaIPv4(configuration.ipAddress) !== undefined &&
      parseJavaIPv4(configuration.subnetMask) !== undefined,
  );

  const result: RouteRow[] = manualRoutes.map((route) => ({
    destinationNetwork: route.destinationNetwork,
    subnetMask: route.subnetMask,
    nextHop: route.gateway,
    interfaceIPAddress: route.interfaceIPAddress,
    origin: 'manual',
    isEditable: true,
  }));

  result.unshift({
    destinationNetwork: '127.0.0.0',
    subnetMask: '255.0.0.0',
    nextHop: '127.0.0.1',
    interfaceIPAddress: '127.0.0.1',
    origin: 'localhost',
    isEditable: false,
  });

  for (const configuration of validInterfaces) {
    const network = networkAddress(configuration.ipAddress, configuration.subnetMask);
    if (network === undefined) continue;
    result.unshift({
      destinationNetwork: network,
      subnetMask: configuration.subnetMask,
      nextHop: configuration.ipAddress,
      interfaceIPAddress: configuration.ipAddress,
      origin: 'connected',
      isEditable: false,
    });
  }

  for (const configuration of validInterfaces) {
    result.unshift({
      destinationNetwork: configuration.ipAddress,
      subnetMask: '255.255.255.255',
      nextHop: '127.0.0.1',
      interfaceIPAddress: '127.0.0.1',
      origin: 'localHost',
      isEditable: false,
    });
  }

  const trimmedGateway = defaultGateway?.trim() ?? '';
  const primaryInterface = validInterfaces[0];
  if (parseJavaIPv4(trimmedGateway) !== undefined && primaryInterface !== undefined) {
    let selectedInterface = primaryInterface.ipAddress;
    for (const configuration of validInterfaces) {
      if (sameNetwork(trimmedGateway, configuration.ipAddress, configuration.subnetMask)) {
        selectedInterface = configuration.ipAddress;
      }
    }
    result.push({
      destinationNetwork: '0.0.0.0',
      subnetMask: '0.0.0.0',
      nextHop: trimmedGateway,
      interfaceIPAddress: selectedInterface,
      origin: 'defaultGateway',
      isEditable: false,
    });
  }

  return result;
}

export function visibleRouteRows(rows: readonly RouteRow[], showAllEntries: boolean): RouteRow[] {
  return showAllEntries ? [...rows] : rows.filter((row) => row.isEditable);
}

/** One row being edited in the route editor. */
export interface RouteDraft {
  readonly id: string;
  destinationNetwork: string;
  subnetMask: string;
  nextGateway: string;
  interfaceIPAddress: string;
  isPendingInsertion: boolean;
}

export function blankRouteDraft(id: string): RouteDraft {
  return {
    id,
    destinationNetwork: '',
    subnetMask: '',
    nextGateway: '',
    interfaceIPAddress: '',
    isPendingInsertion: true,
  };
}

export function routeDraftFromRoute(id: string, route: ManualRoute): RouteDraft {
  return {
    id,
    destinationNetwork: route.destinationNetwork,
    subnetMask: route.subnetMask,
    nextGateway: route.gateway,
    interfaceIPAddress: route.interfaceIPAddress,
    isPendingInsertion: false,
  };
}

/** The route a draft stands for — only once all four cells are valid. */
export function manualRouteFromDraft(draft: RouteDraft): ManualRoute | undefined {
  if (
    !isValidRouteCell(draft.destinationNetwork, 'destination') ||
    !isValidRouteCell(draft.subnetMask, 'subnetMask') ||
    !isValidRouteCell(draft.nextGateway, 'nextGateway') ||
    !isValidRouteCell(draft.interfaceIPAddress, 'interface')
  ) {
    return undefined;
  }
  return {
    destinationNetwork: draft.destinationNetwork,
    subnetMask: draft.subnetMask,
    gateway: draft.nextGateway,
    interfaceIPAddress: draft.interfaceIPAddress,
  };
}

/** At most one blank row waits at the end of the editor. */
export function appendingBlankDraftIfNeeded(
  drafts: readonly RouteDraft[],
  newId: () => string,
): RouteDraft[] {
  if (drafts.some((draft) => draft.isPendingInsertion)) return [...drafts];
  return [...drafts, blankRouteDraft(newId())];
}