/**
 * Shared helpers for the multiplayer server tests: a fake Windmill JWKS
 * endpoint, multiplayer token minting and a server.mjs child process.
 */

import { spawn } from 'node:child_process'
import crypto from 'node:crypto'
import http from 'node:http'
import net from 'node:net'
import path from 'node:path'
import { fileURLToPath } from 'node:url'

const SERVER_PATH = path.join(path.dirname(fileURLToPath(import.meta.url)), '..', 'server.mjs')

export function base64url(buffer) {
  return Buffer.from(buffer).toString('base64url')
}

/**
 * Ask the kernel for an unused port. There is an unavoidable gap between giving
 * the port up and the server.mjs child binding it, so `startMultiplayerServer`
 * retries on EADDRINUSE; servers started in-process bind port 0 directly instead.
 */
async function freePort() {
  return new Promise((resolve, reject) => {
    const probe = net.createServer()
    probe.on('error', reject)
    probe.listen(0, '127.0.0.1', () => {
      const { port } = probe.address()
      probe.close(() => resolve(port))
    })
  })
}

/**
 * Mint a multiplayer JWT in exactly the format the backend produces in
 * `sign_multiplayer` (backend/windmill-api-debug/src/lib.rs): an EdDSA JWT with
 * claims workspace_id, email, iat, exp, purpose.
 */
export function mintToken(privateKey, { workspaceId, email = 'test@windmill.dev', ttlSecs = 300 } = {}) {
  const now = Math.floor(Date.now() / 1000)
  const header = base64url(JSON.stringify({ alg: 'EdDSA', typ: 'JWT' }))
  const claims = base64url(
    JSON.stringify({
      workspace_id: workspaceId,
      email,
      iat: now,
      exp: now + ttlSecs,
      purpose: 'multiplayer'
    })
  )
  const message = `${header}.${claims}`
  const signature = base64url(crypto.sign(null, Buffer.from(message), privateKey))
  return `${message}.${signature}`
}

/**
 * A stand-in for the Windmill backend's /api/debug/jwks, serving the public half
 * of an Ed25519 key pair.
 *
 * With `hold: true` the response is parked indefinitely until `release()` is
 * called. That is what makes the cold-start tests deterministic: the server
 * cannot obtain the key, so the pre-auth window stays open for exactly as long
 * as the test wants, rather than for a wall-clock delay that a slow machine
 * could overrun.
 */
export async function startJwksServer({ hold = false } = {}) {
  const { publicKey, privateKey } = crypto.generateKeyPairSync('ed25519')
  const jwk = publicKey.export({ format: 'jwk' })
  const body = JSON.stringify({
    keys: [{ kty: jwk.kty, crv: jwk.crv, x: jwk.x, kid: 'test', use: 'sig', alg: 'EdDSA' }]
  })
  let requests = 0
  let released = !hold
  const held = new Set()

  const respond = (res) => {
    res.writeHead(200, { 'Content-Type': 'application/json' })
    res.end(body)
  }

  const server = http.createServer((req, res) => {
    if (!req.url?.startsWith('/api/debug/jwks')) {
      res.writeHead(404)
      res.end('not found')
      return
    }
    requests++
    if (released) {
      respond(res)
    } else {
      held.add(res)
    }
  })

  await new Promise((resolve, reject) => {
    server.on('error', reject)
    server.listen(0, '127.0.0.1', resolve)
  })
  const { port } = server.address()

  return {
    privateKey,
    baseUrl: `http://127.0.0.1:${port}`,
    get requests() {
      return requests
    },
    /** Answer every parked request, and any that arrive later. */
    release() {
      released = true
      for (const res of held) respond(res)
      held.clear()
    },
    async close() {
      // Destroy the still-parked responses rather than just dropping them:
      // server.close() waits for in-flight requests, so one left hanging would
      // deadlock teardown.
      for (const res of held) res.destroy()
      held.clear()
      const closed = new Promise((resolve) => server.close(resolve))
      server.closeAllConnections()
      await closed
    }
  }
}

/**
 * Start server.mjs as a child process and resolve once it is listening, retrying
 * if another process grabbed the port between `freePort()` and the child binding.
 */
export async function startMultiplayerServer(env = {}, attemptsLeft = 5) {
  const port = await freePort()
  const child = spawn(process.execPath, [SERVER_PATH], {
    // Pin the settings the tests assert on, so an ambient
    // REQUIRE_SIGNED_MULTIPLAYER_REQUESTS=false cannot turn the rejection tests
    // into false passes, and BASE_INTERNAL_URL cannot stand in for the fake JWKS.
    env: {
      ...process.env,
      REQUIRE_SIGNED_MULTIPLAYER_REQUESTS: 'true',
      BASE_INTERNAL_URL: '',
      PORT: String(port),
      HOST: '127.0.0.1',
      ...env
    },
    stdio: ['ignore', 'pipe', 'pipe']
  })

  let output = ''
  const listening = new Promise((resolve, reject) => {
    const onData = (chunk) => {
      output += chunk.toString()
      if (output.includes('Multiplayer server running')) resolve()
    }
    child.stdout.on('data', onData)
    child.stderr.on('data', onData)
    child.once('error', reject)
    child.once('exit', (code) => reject(new Error(`server exited early (code ${code}):\n${output}`)))
  })

  try {
    await listening
  } catch (error) {
    if (output.includes('EADDRINUSE') && attemptsLeft > 1) {
      return startMultiplayerServer(env, attemptsLeft - 1)
    }
    throw error
  }

  return {
    port,
    url: `ws://127.0.0.1:${port}`,
    get output() {
      return output
    },
    /** How the child died, or null while it is still running. */
    get exitStatus() {
      if (child.exitCode !== null) return `exited with code ${child.exitCode}`
      if (child.signalCode !== null) return `killed by ${child.signalCode}`
      return null
    },
    async close() {
      if (child.exitCode !== null) return
      const exited = new Promise((resolve) => child.once('exit', resolve))
      child.kill('SIGKILL')
      await exited
    }
  }
}

/**
 * Start server.mjs and wait for it to exit, for the cases where it is expected
 * to fail rather than come up. Returns how it died and everything it printed.
 */
export async function runMultiplayerServerUntilExit(env = {}, { timeoutMs = 15000 } = {}) {
  const child = spawn(process.execPath, [SERVER_PATH], {
    env: {
      ...process.env,
      REQUIRE_SIGNED_MULTIPLAYER_REQUESTS: 'true',
      BASE_INTERNAL_URL: '',
      HOST: '127.0.0.1',
      ...env
    },
    stdio: ['ignore', 'pipe', 'pipe']
  })

  let output = ''
  child.stdout.on('data', (chunk) => { output += chunk.toString() })
  child.stderr.on('data', (chunk) => { output += chunk.toString() })

  // Record the rescue rather than inferring it from the exit signal: `signal` is
  // null for every child exit on Windows, so a caller checking it could not tell
  // a server that exited on its own from one this had to kill.
  let killedByTimeout = false
  const killer = setTimeout(() => {
    // Claim the rescue only if there was something to rescue. The child may have
    // exited moments ago with 'close' still pending on the stdio drain — the very
    // window this helper waits for — and killing a corpse is not an intervention.
    if (child.exitCode !== null || child.signalCode !== null) return
    killedByTimeout = child.kill('SIGKILL')
  }, timeoutMs)

  try {
    // 'close' rather than 'exit': 'exit' fires when the child terminates, which
    // can be before its stdio pipes have been drained, and the caller reads
    // `output`. A child that never starts emits neither, only 'error'.
    const [code, signal] = await new Promise((resolve, reject) => {
      child.once('close', (exitCode, exitSignal) => resolve([exitCode, exitSignal]))
      child.once('error', reject)
    })
    return { code, signal, output, killedByTimeout }
  } finally {
    clearTimeout(killer)
  }
}

/** Poll `predicate` until it is true, or throw after `timeoutMs`. */
export async function waitFor(predicate, { timeoutMs = 15000, intervalMs = 10, message = 'condition' } = {}) {
  const deadline = Date.now() + timeoutMs
  while (Date.now() < deadline) {
    if (await predicate()) return
    await new Promise((resolve) => setTimeout(resolve, intervalMs))
  }
  throw new Error(`Timed out after ${timeoutMs}ms waiting for ${message}`)
}