import * as plugins from './plugins.js';
import type { INetworkManagerOptions, ITapDevice } from './interfaces/index.js';
import { SmartVMError } from './interfaces/index.js';

type TShellExecResult = Awaited<ReturnType<InstanceType<typeof plugins.smartshell.Smartshell>['execSpawn']>>;

interface IParsedSubnet {
  networkAddress: number;
  broadcastAddress: number;
  cidr: number;
  subnetMask: string;
}

/**
 * Manages host networking for Firecracker VMs.
 * Creates TAP devices, Linux bridges, and configures NAT for VM internet access.
 */
export class NetworkManager {
  private bridgeName: string;
  private subnetBase: string;
  private subnetCidr: number;
  private gatewayIp: string;
  private subnetMask: string;
  private nextIpAddress: number;
  private lastUsableIpAddress: number;
  private activeTaps: Map<string, ITapDevice> = new Map();
  private bridgeCreated: boolean = false;
  private defaultRouteInterface: string | null = null;
  private shell: InstanceType<typeof plugins.smartshell.Smartshell>;

  constructor(options: INetworkManagerOptions = {}) {
    this.bridgeName = options.bridgeName || 'svbr0';
    this.validateInterfaceName(this.bridgeName, 'bridgeName');
    const subnet = options.subnet || '172.30.0.0/24';
    const parsedSubnet = this.parseSubnet(subnet);

    this.subnetBase = this.intToIp(parsedSubnet.networkAddress);
    this.subnetCidr = parsedSubnet.cidr;
    this.subnetMask = parsedSubnet.subnetMask;
    this.gatewayIp = this.intToIp(parsedSubnet.networkAddress + 1);
    this.nextIpAddress = parsedSubnet.networkAddress + 2;
    this.lastUsableIpAddress = parsedSubnet.broadcastAddress - 1;

    this.shell = new plugins.smartshell.Smartshell({ executor: 'bash' });
  }

  /**
   * Parse an IPv4 CIDR subnet and ensure there is room for a gateway and guests.
   */
  private parseSubnet(subnet: string): IParsedSubnet {
    const [ip, cidrText, extra] = subnet.split('/');
    const cidr = Number(cidrText);
    if (!ip || !cidrText || extra !== undefined || !Number.isInteger(cidr) || cidr < 1 || cidr > 30) {
      throw new SmartVMError(
        `Invalid subnet '${subnet}': expected IPv4 CIDR with prefix length 1-30`,
        'INVALID_SUBNET',
      );
    }

    const ipAddress = this.ipToInt(ip);
    const mask = this.cidrToMask(cidr);
    const networkAddress = (ipAddress & mask) >>> 0;
    const hostCount = 2 ** (32 - cidr);
    const broadcastAddress = networkAddress + hostCount - 1;
    if (hostCount < 4) {
      throw new SmartVMError(
        `Invalid subnet '${subnet}': at least two usable host addresses are required`,
        'INVALID_SUBNET',
      );
    }

    return {
      networkAddress,
      broadcastAddress,
      cidr,
      subnetMask: this.intToIp(mask),
    };
  }

  private ipToInt(ip: string): number {
    const octets = ip.split('.');
    if (octets.length !== 4) {
      throw new SmartVMError(`Invalid IPv4 address '${ip}'`, 'INVALID_SUBNET');
    }

    if (octets.some((octet) => !/^[0-9]+$/.test(octet))) {
      throw new SmartVMError(`Invalid IPv4 address '${ip}'`, 'INVALID_SUBNET');
    }

    const numbers = octets.map((octet) => Number(octet));
    if (numbers.some((octet) => !Number.isInteger(octet) || octet < 0 || octet > 255)) {
      throw new SmartVMError(`Invalid IPv4 address '${ip}'`, 'INVALID_SUBNET');
    }

    return (
      numbers[0] * 256 ** 3 +
      numbers[1] * 256 ** 2 +
      numbers[2] * 256 +
      numbers[3]
    ) >>> 0;
  }

  private intToIp(address: number): string {
    return [
      Math.floor(address / 256 ** 3) % 256,
      Math.floor(address / 256 ** 2) % 256,
      Math.floor(address / 256) % 256,
      address % 256,
    ].join('.');
  }

  private cidrToMask(cidr: number): number {
    return (0xffffffff << (32 - cidr)) >>> 0;
  }

  private validateInterfaceName(name: string, fieldName: string): void {
    if (!/^[a-zA-Z0-9][a-zA-Z0-9_.:-]{0,14}$/.test(name)) {
      throw new SmartVMError(
        `${fieldName} '${name}' is not a valid Linux interface name`,
        'INVALID_INTERFACE_NAME',
      );
    }
  }

  /**
   * Allocate the next available IP address in the subnet.
   */
  public allocateIp(): string {
    if (this.nextIpAddress > this.lastUsableIpAddress) {
      throw new SmartVMError(
        `Subnet ${this.subnetBase}/${this.subnetCidr} has no available guest IP addresses`,
        'IP_EXHAUSTED',
      );
    }

    const ip = this.intToIp(this.nextIpAddress);
    this.nextIpAddress++;
    return ip;
  }

  /**
   * Generate a deterministic locally-administered MAC address.
   */
  public generateMac(vmId: string, ifaceId: string): string {
    // Create a simple hash from vmId + ifaceId for deterministic MAC generation
    const input = `${vmId}:${ifaceId}`;
    let hash = 0;
    for (let i = 0; i < input.length; i++) {
      const char = input.charCodeAt(i);
      hash = ((hash << 5) - hash) + char;
      hash = hash & hash; // Convert to 32-bit integer
    }

    // Ensure hash is positive
    const h = Math.abs(hash);

    // Generate MAC octets from hash, using locally-administered prefix (02:xx:xx:xx:xx:xx)
    const mac = [
      0x02,
      (h >> 0) & 0xff,
      (h >> 8) & 0xff,
      (h >> 16) & 0xff,
      (h >> 24) & 0xff,
      ((h >> 4) ^ (h >> 12)) & 0xff,
    ];

    return mac.map((b) => b.toString(16).padStart(2, '0')).join(':');
  }

  /**
   * Generate a TAP device name that fits within IFNAMSIZ (15 chars).
   * Format: sv<4charVmId><ifaceId truncated>
   */
  public generateTapName(vmId: string, ifaceId: string): string {
    const vmPart = vmId.replace(/-/g, '').substring(0, 4);
    const ifacePart = ifaceId.substring(0, 6);
    const tapName = `sv${vmPart}${ifacePart}`;
    // Ensure max 15 chars (Linux IFNAMSIZ)
    return tapName.substring(0, 15);
  }

  private async run(command: string, args: string[]): Promise<TShellExecResult> {
    return this.shell.execSpawn(command, args, { silent: true });
  }

  private async runChecked(command: string, args: string[]): Promise<TShellExecResult> {
    const result = await this.run(command, args);
    if (result.exitCode !== 0) {
      const output = (result.stderr || result.stdout || '').trim();
      throw new Error(`${command} ${args.join(' ')} exited with code ${result.exitCode}${output ? `: ${output}` : ''}`);
    }
    return result;
  }

  private async getDefaultRouteInterface(): Promise<string> {
    if (this.defaultRouteInterface) {
      return this.defaultRouteInterface;
    }

    const result = await this.runChecked('ip', ['route', 'show', 'default']);
    const match = result.stdout.match(/\bdev\s+([^\s]+)/);
    if (!match) {
      throw new Error('Could not determine default route interface');
    }

    const iface = match[1];
    this.validateInterfaceName(iface, 'default route interface');
    this.defaultRouteInterface = iface;
    return iface;
  }

  /**
   * Ensure the Linux bridge is created and configured.
   */
  public async ensureBridge(): Promise<void> {
    if (this.bridgeCreated) return;

    try {
      // Check if bridge already exists
      const result = await this.run('ip', ['link', 'show', this.bridgeName]);
      if (result.exitCode !== 0) {
        // Create bridge
        await this.runChecked('ip', ['link', 'add', this.bridgeName, 'type', 'bridge']);
        await this.runChecked('ip', ['addr', 'add', `${this.gatewayIp}/${this.subnetCidr}`, 'dev', this.bridgeName]);
        await this.runChecked('ip', ['link', 'set', this.bridgeName, 'up']);
      }

      // Enable IP forwarding
      await this.runChecked('sysctl', ['-w', 'net.ipv4.ip_forward=1']);

      // Set up NAT masquerade (idempotent with -C check)
      const defaultIface = await this.getDefaultRouteInterface();
      const natArgs = [
        '-t',
        'nat',
        '-C',
        'POSTROUTING',
        '-s',
        `${this.subnetBase}/${this.subnetCidr}`,
        '-o',
        defaultIface,
        '-j',
        'MASQUERADE',
      ];
      const checkResult = await this.run('iptables', natArgs);
      if (checkResult.exitCode !== 0) {
        await this.runChecked('iptables', [
          '-t',
          'nat',
          '-A',
          'POSTROUTING',
          '-s',
          `${this.subnetBase}/${this.subnetCidr}`,
          '-o',
          defaultIface,
          '-j',
          'MASQUERADE',
        ]);
      }

      this.bridgeCreated = true;
    } catch (err) {
      const message = err instanceof Error ? err.message : String(err);
      throw new SmartVMError(
        `Failed to set up network bridge: ${message}`,
        'BRIDGE_SETUP_FAILED',
      );
    }
  }

  /**
   * Create a TAP device for a VM and attach it to the bridge.
   */
  public async createTapDevice(vmId: string, ifaceId: string): Promise<ITapDevice> {
    await this.ensureBridge();

    const tapName = this.generateTapName(vmId, ifaceId);
    this.validateInterfaceName(tapName, 'tapName');
    const guestIp = this.allocateIp();
    const mac = this.generateMac(vmId, ifaceId);
    let tapCreated = false;

    try {
      // Create TAP device
      await this.runChecked('ip', ['tuntap', 'add', 'dev', tapName, 'mode', 'tap']);
      tapCreated = true;
      // Attach to bridge
      await this.runChecked('ip', ['link', 'set', tapName, 'master', this.bridgeName]);
      // Bring TAP device up
      await this.runChecked('ip', ['link', 'set', tapName, 'up']);

      const tap: ITapDevice = {
        tapName,
        guestIp,
        gatewayIp: this.gatewayIp,
        subnetMask: this.subnetMask,
        mac,
      };

      this.activeTaps.set(tapName, tap);
      return tap;
    } catch (err) {
      if (tapCreated) {
        await this.removeTapDevice(tapName);
      }
      const message = err instanceof Error ? err.message : String(err);
      throw new SmartVMError(
        `Failed to create TAP device ${tapName}: ${message}`,
        'TAP_CREATE_FAILED',
      );
    }
  }

  /**
   * Remove a TAP device and free its resources.
   */
  public async removeTapDevice(tapName: string): Promise<void> {
    this.validateInterfaceName(tapName, 'tapName');
    try {
      await this.run('ip', ['link', 'del', tapName]);
      this.activeTaps.delete(tapName);
    } catch {
      // Device may already be gone
    }
  }

  /**
   * Generate kernel boot args for guest networking.
   * Returns the `ip=` parameter for the kernel command line.
   */
  public getGuestNetworkBootArgs(tap: ITapDevice): string {
    // Format: ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>::<device>:off
    return `ip=${tap.guestIp}::${tap.gatewayIp}:${tap.subnetMask}::eth0:off`;
  }

  /**
   * Get all active TAP devices.
   */
  public getActiveTaps(): ITapDevice[] {
    return Array.from(this.activeTaps.values());
  }

  /**
   * Clean up all TAP devices and the bridge.
   */
  public async cleanup(): Promise<void> {
    // Remove all TAP devices
    for (const tapName of Array.from(this.activeTaps.keys())) {
      await this.removeTapDevice(tapName);
    }

    // Remove bridge if we created it
    if (this.bridgeCreated) {
      try {
        await this.run('ip', ['link', 'set', this.bridgeName, 'down']);
        await this.run('ip', ['link', 'del', this.bridgeName]);
      } catch {
        // Bridge may already be gone
      }

      // Remove NAT rule
      try {
        const defaultIface = this.defaultRouteInterface || await this.getDefaultRouteInterface();
        await this.run('iptables', [
          '-t',
          'nat',
          '-D',
          'POSTROUTING',
          '-s',
          `${this.subnetBase}/${this.subnetCidr}`,
          '-o',
          defaultIface,
          '-j',
          'MASQUERADE',
        ]);
      } catch {
        // Rule may not exist
      }

      this.bridgeCreated = false;
    }
  }
}