/**
 * @sutong/dsh-lan-access — host half.
 *
 * Publishes the loopback dsh Web UI on the LAN through a standalone reverse
 * proxy. `dsh web --host 0.0.0.0` is refused by the shipped CLI on purpose
 * (it would expose remote code execution to the network), so this plugin keeps
 * the official server on loopback and adds a second listener that forwards to
 * it. The official browser-trust fence and the launch-token login stay in
 * force; nothing about the composed application is overridden.
 *
 * @module @sutong/dsh-lan-access
 */

import { createServer, request as httpRequest } from 'node:http'
import { connect as netConnect, isIPv4 } from 'node:net'
import { networkInterfaces } from 'node:os'
import z from '@deepseek-ai/schemastery'

/** Stable Cordis plugin name. */
export const name = 'dsh-lan-access'

/** Services required before the LAN listener resolves its upstream. */
export const inject = ['webServer']

/**
 * Configuration for the LAN listener. Every value also lives in the profile's
 * `cordis.patch.yml` row config, so it survives plugin upgrades.
 */
export const Config = z.object({
  /** Whether the LAN listener runs at all. @default true */
  enabled: z.boolean().default(true),
  /** Listener address; `0.0.0.0` publishes on every interface. @default '0.0.0.0' */
  host: z.string().default('0.0.0.0'),
  /**
   * Listener port. The default avoids 3081, which the community
   * `dsh-lan-proxy` plugin also claims by default, so the two can coexist.
   * @default 3082
   */
  port: z.number().default(3082),
  /**
   * Upstream host. Only a loopback authority is accepted, so the plugin can
   * never become an open forward proxy (SSRF guard). @default '127.0.0.1'
   */
  targetHost: z.string().default('127.0.0.1'),
  /**
   * Upstream port, or 0 to follow the live `webServer` port. @default 0
   */
  targetPort: z.number().default(0),
  /** Print the LAN URLs (with launch token) at startup. @default true */
  printBanner: z.boolean().default(true),
  /**
   * Declare the page-side topology fact `ownsHost` for non-loopback pages.
   *
   * The official client derives `isLoopback` from `location.hostname`, and the
   * durable settings surface is loopback-only by that rule: on a LAN page the
   * settings mirror stays in `memory` mode, so the Models/provider pages fail
   * with "settings are unavailable in this browser" and the config-file action
   * disappears. The Host/Origin fence and the launch-token login are unaffected
   * by this fact, so enabling it restores the settings UI rather than granting
   * new server-side authority — but that UI reads and writes server settings,
   * credentials included. Keep it off unless every device on this network is
   * trusted. @default false
   */
  ownsHostCompat: z.boolean().default(false),
})

/** Exact route the Web UI panel reads its LAN facts from. */
export const SUMMARY_PATH = '/api/dsh-lan-access/summary'

/** Connection-owned hop-by-hop headers this proxy never forwards. */
const HOP_BY_HOP = new Set([
  'connection',
  'keep-alive',
  'proxy-authenticate',
  'proxy-authorization',
  'te',
  'trailer',
  'transfer-encoding',
  'upgrade',
])

/** Names that always mean the local machine. */
const LOOPBACK_NAMES = new Set(['localhost', '::1', '0:0:0:0:0:0:0:1'])

/**
 * Whether a host names the local loopback authority.
 * @param host - a bare hostname or IP literal, without a port.
 * @returns true for localhost, IPv6 loopback, or any 127/8 address.
 */
function isLoopbackHost(host) {
  if (typeof host !== 'string' || host === '') return false
  const bare = host.toLowerCase().replaceAll('[', '').replaceAll(']', '')
  if (LOOPBACK_NAMES.has(bare)) return true
  return isIPv4(bare) && bare.startsWith('127.')
}

/**
 * Strip the port from an HTTP `Host` / authority value.
 * @param authority - `host`, `host:port`, or `[v6]:port`.
 * @returns the bare host, or the input when it cannot be split.
 */
function hostnameOf(authority) {
  if (typeof authority !== 'string') return ''
  const value = authority.trim()
  if (value.startsWith('[')) {
    const end = value.indexOf(']')
    return end === -1 ? value : value.slice(1, end)
  }
  const colon = value.indexOf(':')
  return colon === -1 ? value : value.slice(0, colon)
}

/**
 * Every non-internal IPv4 address this machine currently holds. These are the
 * addresses a peer on the same network can reach.
 * @returns addresses in interface order, link-local autoconf excluded.
 */
function lanIPv4Addresses() {
  const found = []
  for (const entries of Object.values(networkInterfaces())) {
    for (const entry of entries ?? []) {
      if (entry.family !== 'IPv4' || entry.internal) continue
      if (entry.address.startsWith('169.254.')) continue
      found.push(entry.address)
    }
  }
  return found
}

/**
 * Rewrite one outbound request's headers for the loopback upstream.
 *
 * `Host` must name a loopback authority because the official `/api` fence
 * accepts only loopback or declared authorities, and the browser cookie is
 * authority-bound. `Origin` must then match the rewritten `Host`, or the fence
 * rejects an otherwise same-origin request. The browser keeps its own cookie
 * jar keyed by the address it actually requested, so cookies need no rewriting
 * on the way back.
 * @param headers - incoming request headers.
 * @param authority - the upstream `host:port` to present.
 * @param preserve - lowercase names to keep even though they are hop-by-hop (the WebSocket handshake).
 * @returns a new header record safe to send upstream.
 */
function upstreamHeaders(headers, authority, preserve = EMPTY_PRESERVE) {
  const out = {}
  for (const [key, value] of Object.entries(headers)) {
    if (value === undefined) continue
    const lower = key.toLowerCase()
    if (HOP_BY_HOP.has(lower) && !preserve.has(lower)) continue
    out[key] = value
  }
  out.host = authority
  if (typeof out.origin === 'string') out.origin = `http://${authority}`
  return out
}

/**
 * Hop-by-hop names the WebSocket handshake itself must keep: stripping them
 * would downgrade the forwarded request to a plain GET, so the upstream would
 * answer 200 with a body instead of switching protocols.
 */
const UPGRADE_PRESERVE = new Set(['connection', 'upgrade'])

/** Shared empty set, so the common path allocates nothing. */
const EMPTY_PRESERVE = new Set()

/**
 * Forward one upgraded (WebSocket) socket to the upstream server.
 *
 * The handshake is re-emitted byte-for-byte with only `Host`/`Origin`
 * rewritten, so `permessage-deflate` and every other extension negotiate
 * end-to-end between the browser and the upstream — this proxy never
 * decompresses a frame.
 * @param req - the incoming upgrade request.
 * @param clientSocket - the browser-side socket, owned on return.
 * @param head - bytes already read past the handshake.
 * @param options - `authority` plus the upstream `host`/`port` to dial.
 */
function forwardUpgrade(req, clientSocket, head, options) {
  const { authority, host, port } = options
  const headers = upstreamHeaders(req.headers, authority, UPGRADE_PRESERVE)
  let raw = `${req.method ?? 'GET'} ${req.url ?? '/'} HTTP/1.1\r\n`
  for (const [key, value] of Object.entries(headers)) {
    for (const item of Array.isArray(value) ? value : [value]) raw += `${key}: ${item}\r\n`
  }
  raw += '\r\n'

  const upstream = netConnect(port, host, () => {
    upstream.write(raw)
    if (head !== undefined && head.length > 0) upstream.write(head)
    upstream.pipe(clientSocket)
    clientSocket.pipe(upstream)
  })
  const bail = () => {
    upstream.destroy()
    clientSocket.destroy()
  }
  upstream.on('error', bail)
  clientSocket.on('error', bail)
}

/**
 * Head script that declares `ownsHost` for a non-loopback page only.
 *
 * It stays inert on a loopback page, where the official client already treats
 * the browser as local, and mutates nothing but the one topology flag.
 */
export const OWNS_HOST_COMPAT_SCRIPT = [
  '(function () {',
  '  try {',
  '    var host = globalThis.location && globalThis.location.hostname;',
  '    if (!host) return;',
  '    if (host === "localhost" || host === "[::1]" || host.indexOf("127.") === 0) return;',
  '    var transport = globalThis.__DSH_TRANSPORT__ || {};',
  '    transport.ownsHost = true;',
  '    globalThis.__DSH_TRANSPORT__ = transport;',
  '  } catch (error) { /* leave the page topology untouched */ }',
  '})();',
].join('\n')

/**
 * Insert an inline classic script immediately before `</head>`, so it runs
 * before the deferred module bundle reads `__DSH_TRANSPORT__`.
 * @param html - the raw index document.
 * @param text - script body; must not contain `</script`.
 * @returns the document with the script inserted.
 */
function withHeadScript(html, text) {
  const tag = `<script>${text}</script>`
  const at = html.indexOf('</head>')
  return at === -1 ? `${tag}${html}` : `${html.slice(0, at)}${tag}${html.slice(at)}`
}

/**
 * Mount the LAN listener, the panel's data route, and the startup banner.
 * @param ctx - plugin context carrying the web server and connection services.
 * @param config - validated {@link Config}.
 */
export function apply(ctx, config) {
  const settings = { ...config }

  if (settings.enabled === false) return
  if (!isLoopbackHost(settings.targetHost)) {
    console.warn(
      `dsh-lan-access: refusing targetHost ${JSON.stringify(settings.targetHost)}; only a loopback upstream is allowed (this plugin is not an open proxy)`,
    )
    return
  }
  if (!Number.isInteger(settings.port) || settings.port <= 0 || settings.port > 65535) {
    console.warn(`dsh-lan-access: refusing invalid port ${String(settings.port)}`)
    return
  }

  /** Resolve the live upstream port; `targetPort: 0` follows the web server. */
  const upstreamPort = () => {
    if (Number.isInteger(settings.targetPort) && settings.targetPort > 0) return settings.targetPort
    const live = ctx.get('webServer')?.port
    return typeof live === 'number' && live > 0 ? live : 3080
  }
  const upstreamAuthority = () => `${settings.targetHost}:${String(upstreamPort())}`

  /** LAN facts for the banner and the Web UI panel. */
  const summary = () => {
    const connection = ctx.get('connection')
    const port = settings.port
    return {
      enabled: true,
      listening: listened,
      ...(bindError === undefined ? {} : { bindError }),
      listen: { host: settings.host, port },
      target: { host: settings.targetHost, port: upstreamPort() },
      lan: lanIPv4Addresses().map((address) => {
        const url = `http://${address}:${String(port)}/`
        return {
          address,
          url,
          tokenUrl: connection === undefined ? url : connection.authenticatedUrl(url),
        }
      }),
    }
  }

  let listened = false
  let announced = false
  /** Set when the listener could not bind; surfaced to the panel. */
  let bindError
  const announce = (connection) => {
    if (announced || !listened || settings.printBanner === false) return
    announced = true
    console.log(
      `dsh-lan-access: 0.0.0.0:${String(settings.port)} → http://${upstreamAuthority()} (LAN listener)`,
    )
    const addresses = lanIPv4Addresses()
    if (addresses.length === 0) {
      console.log('dsh-lan-access: no non-internal IPv4 address found; no LAN URL to print')
    }
    for (const address of addresses) {
      const url = `http://${address}:${String(settings.port)}/`
      const tokenUrl = connection === undefined ? url : connection.authenticatedUrl(url)
      console.log(`dsh-lan-access:   ${tokenUrl}`)
    }
    console.log(
      'dsh-lan-access: that link carries the launch token and grants full dsh control (shell included) — keep it on a trusted network',
    )
  }

  // The browser URL the panel is served from may be the loopback one, so the
  // data route is reachable both directly and through the listener.
  ctx.inject(['webServer', 'connection'], (routeCtx) => {
    routeCtx.effect(
      () =>
        routeCtx.webServer.register({
          kind: 'exact',
          path: SUMMARY_PATH,
          handler: (req, res) => {
            const admission = routeCtx.connection.admit(req)
            if ('rejection' in admission) {
              res.writeHead(admission.rejection, { 'content-type': 'text/plain; charset=utf-8' })
              res.end(admission.rejection === 401 ? 'unauthorized' : 'forbidden')
              return
            }
            const body = JSON.stringify(summary())
            res.writeHead(200, {
              'content-type': 'application/json; charset=utf-8',
              'cache-control': 'no-store',
              'content-length': Buffer.byteLength(body),
            })
            res.end(body)
          },
        }),
      'dsh-lan-access: LAN summary route',
    )
  })

  if (settings.ownsHostCompat) {
    ctx.inject(['webServer'], (compatCtx) => {
      compatCtx.effect(
        () => compatCtx.webServer.tapIndex((html) => withHeadScript(html, OWNS_HOST_COMPAT_SCRIPT)),
        'dsh-lan-access: ownsHost compat index tap',
      )
    })
  }

  const server = createServer((req, res) => {
    const authority = upstreamAuthority()
    const upstream = httpRequest(
      {
        host: settings.targetHost,
        port: upstreamPort(),
        method: req.method,
        path: req.url,
        headers: upstreamHeaders(req.headers, authority),
      },
      (up) => {
        const out = {}
        for (const [key, value] of Object.entries(up.headers)) {
          if (value === undefined) continue
          if (HOP_BY_HOP.has(key.toLowerCase())) continue
          out[key] = value
        }
        res.writeHead(up.statusCode ?? 502, out)
        up.pipe(res)
      },
    )
    upstream.on('error', (error) => {
      if (!res.headersSent) {
        res.writeHead(502, { 'content-type': 'text/plain; charset=utf-8' })
      }
      res.end(`dsh-lan-access: upstream error: ${error.message}`)
    })
    req.pipe(upstream)
  })

  server.on('upgrade', (req, socket, head) => {
    const authority = upstreamAuthority()
    const host = hostnameOf(req.headers.host)
    const isLocal =
      host === '' ||
      host === settings.host ||
      isLoopbackHost(host) ||
      lanIPv4Addresses().includes(host)
    if (!isLocal) {
      // DNS-rebinding guard: only address-literal/localhost authorities may
      // reach the upstream, so a hostile name cannot point here.
      socket.destroy()
      return
    }
    forwardUpgrade(req, socket, head, {
      authority,
      host: settings.targetHost,
      port: upstreamPort(),
    })
  })

  server.on('error', (error) => {
    bindError = error.message
    const hint =
      error.code === 'EADDRINUSE'
        ? ' — another process or plugin already holds that port (the community dsh-lan-proxy plugin defaults to 3081)'
        : ''
    console.warn(
      `dsh-lan-access: LAN listener unavailable on ${settings.host}:${String(settings.port)} because ${error.message}${hint}`,
    )
  })

  ctx.effect(
    () => () => {
      server.closeAllConnections?.()
      server.close()
    },
    'dsh-lan-access: LAN listener',
  )

  server.listen(settings.port, settings.host, () => {
    listened = true
    announce(ctx.get('connection'))
  })

  ctx.inject(['connection'], (connectionCtx) => {
    announce(connectionCtx.connection)
  })
}

/** Test hooks; production never mutates them. */
export const internals = {
  isLoopbackHost,
  hostnameOf,
  lanIPv4Addresses,
  upstreamHeaders,
  withHeadScript,
}