lan.ts

import { Socket, createSocket, RemoteInfo } from 'dgram'
import { EventEmitter } from 'events'

export const LAN_MULTICAST_ADDR = '224.0.2.60'
export const LAN_MULTICAST_ADDR_V6 = 'FF75:230::60'
export const LAN_MULTICAST_PORT = 4445

export interface MinecraftLanDiscover {
  on(channel: 'discover', listener: (event: LanServerInfo & { remote: RemoteInfo }) => void): this
  once(channel: 'discover', listener: (event: LanServerInfo & { remote: RemoteInfo }) => void): this
  addListener(channel: 'discover', listener: (event: LanServerInfo & { remote: RemoteInfo }) => void): this
  removeListener(channel: 'discover', listener: (event: LanServerInfo & { remote: RemoteInfo }) => void): this
}

export class MinecraftLanDiscover extends EventEmitter {
  readonly socket: Socket

  #ready = false
  #group: string

  get isReady() {
    return this.#ready
  }

  constructor(type: 'udp4' | 'udp6' = 'udp4') {
    super()
    const sock = createSocket({ type, reuseAddr: true })

    this.#group = type === 'udp4' ? LAN_MULTICAST_ADDR : LAN_MULTICAST_ADDR_V6

    sock.on('listening', () => {
      const address = sock.address()
      sock.addMembership(this.#group, type === 'udp4' ? address.address : undefined)
      sock.setMulticastTTL(128)
      sock.setBroadcast(true)
      this.#ready = true
    })

    sock.on('message', (buf, remote) => {
      const content = buf.toString('utf-8')

      const motdRegx = /\[MOTD\](.+)\[\/MOTD\]/g
      const portRegx = /\[AD\](.+)\[\/AD\]/g

      const portResult = portRegx.exec(content)
      if (!portResult || !portResult[1]) {
        // emit error
      } else {
        const motd = motdRegx.exec(content)?.[1] ?? ''
        const port = Number.parseInt(portResult[1])
        this.emit('discover', { motd, port, remote })
      }
    })

    this.socket = sock
  }

  broadcast(inf: LanServerInfo) {
    return new Promise<number>((resolve, reject) => {
      this.socket.send(`[MOTD]${inf.motd}[/MOTD][AD]${inf.port}[/AD]`, LAN_MULTICAST_PORT, this.#group, (err, bytes) => {
        if (err) reject(err)
        else resolve(bytes)
      })
    })
  }

  bind(): Promise<void> {
    return new Promise((resolve, reject) => {
      this.socket.bind(LAN_MULTICAST_PORT, () => {
        resolve()
      }).once('error', (e) => {
        reject(e)
      })
    })
  }

  destroy(): Promise<void> {
    return new Promise((resolve) => {
      this.socket.close(resolve)
    })
  }
}

export interface LanServerInfo {
  motd: string
  port: number
}