/**
 * dsh-fleet-control — host half.
 *
 * Persists the set of session ids that "Stop All" gracefully cancelled so that
 * "Resume All" can re-prompt exactly those sessions later — including after an
 * app restart. State lives in ~/.dsh/fleet-control/stopped.json.
 *
 * Exposes one loopback-only route, GET/POST /fleet/stopped:
 *   GET  -> { ok: true, value: { ids: string[], updatedAt: string } }
 *   POST { ids: string[] } -> replaces the set, returns the same envelope.
 *
 * @module dsh-fleet-control
 */
import { mkdir, readFile, rename, writeFile } from 'node:fs/promises'
import { homedir } from 'node:os'
import { dirname, join } from 'node:path'

const STORE_FILE = join(process.env.DSH_HOME?.trim() || join(homedir(), '.dsh'), 'fleet-control', 'stopped.json')

export const name = 'dsh-fleet-control'
export const inject = ['webServer']

const JSON_HEADERS = {
  'content-type': 'application/json; charset=utf-8',
  'referrer-policy': 'no-referrer',
}

function writeJson(response, status, body) {
  response.writeHead(status, JSON_HEADERS)
  response.end(JSON.stringify(body))
}

// ---- loopback guards (mirrors dsh-open-in-smerge) -------------------------
function isIPv4Loopback(address) {
  const parts = address.split('.')
  return parts.length === 4
    && parts[0] === '127'
    && parts.every(part => /^\d{1,3}$/.test(part) && Number(part) <= 255)
}

function isLoopbackAddress(address) {
  if (address === undefined) return false
  const normalized = address.toLowerCase()
  if (normalized === '::1') return true
  if (normalized.startsWith('::ffff:')) return isIPv4Loopback(normalized.slice('::ffff:'.length))
  return isIPv4Loopback(normalized)
}

function isLoopbackHostname(hostname) {
  return hostname === 'localhost' || hostname === '[::1]' || isIPv4Loopback(hostname)
}

export function isLoopbackRequest(request) {
  if (!isLoopbackAddress(request.socket?.remoteAddress)) return false

  const host = request.headers.host
  if (typeof host !== 'string') return false

  let hostUrl
  try {
    hostUrl = new URL(`http://${host}`)
  } catch {
    return false
  }

  if (!isLoopbackHostname(hostUrl.hostname)) return false
  if (request.headers['sec-fetch-site'] === 'cross-site') return false

  const origin = request.headers.origin
  if (origin === undefined) return true

  try {
    return new URL(origin).host === hostUrl.host
  } catch {
    return false
  }
}
// --------------------------------------------------------------------------

async function readJsonBody(request) {
  const chunks = []
  let size = 0

  for await (const chunk of request) {
    size += chunk.length
    if (size > 64 * 1024) {
      request.destroy()
      return null
    }
    chunks.push(chunk)
  }

  if (chunks.length === 0) return null

  try {
    const parsed = JSON.parse(Buffer.concat(chunks).toString('utf8'))
    return typeof parsed === 'object' && parsed !== null && !Array.isArray(parsed) ? parsed : null
  } catch {
    return null
  }
}

function sanitizeIds(value) {
  if (!Array.isArray(value)) return []
  const out = []
  for (const entry of value) {
    if (typeof entry === 'string' && entry !== '' && out.indexOf(entry) === -1) out.push(entry)
  }
  return out
}

export class StoppedSessionStore {
  constructor(filePath = STORE_FILE) {
    this.filePath = filePath
    this.ids = []
    this.updatedAt = new Date(0).toISOString()
    this.ready = this.load()
    this.pendingWrite = Promise.resolve()
  }

  async load() {
    try {
      const parsed = JSON.parse(await readFile(this.filePath, 'utf8'))
      if (typeof parsed !== 'object' || parsed === null || Array.isArray(parsed)) return
      this.ids = sanitizeIds(parsed.ids)
      if (typeof parsed.updatedAt === 'string') this.updatedAt = parsed.updatedAt
    } catch {
      this.ids = []
    }
  }

  async get() {
    await this.ready
    return { ids: this.ids.slice(), updatedAt: this.updatedAt }
  }

  async set(ids) {
    await this.ready
    this.ids = sanitizeIds(ids)
    this.updatedAt = new Date().toISOString()
    this.pendingWrite = this.pendingWrite.then(() => this.persist())
    await this.pendingWrite
    return { ids: this.ids.slice(), updatedAt: this.updatedAt }
  }

  async persist() {
    await mkdir(dirname(this.filePath), { recursive: true })
    const temporaryPath = `${this.filePath}.tmp-${process.pid}`
    const body = JSON.stringify({ ids: this.ids, updatedAt: this.updatedAt }, null, 2)
    await writeFile(temporaryPath, `${body}\n`, 'utf8')
    await rename(temporaryPath, this.filePath)
  }
}

export function apply(context) {
  const store = new StoppedSessionStore()

  const handler = async (request, response) => {
    const method = (request.method ?? 'GET').toUpperCase()

    if (method !== 'GET' && method !== 'POST') {
      writeJson(response, 405, { ok: false, error: { code: 'method-not-allowed', message: 'method not allowed' } })
      return
    }

    if (!isLoopbackRequest(request)) {
      writeJson(response, 403, { ok: false, error: { code: 'forbidden', message: 'loopback only' } })
      return
    }

    if (method === 'GET') {
      writeJson(response, 200, { ok: true, value: await store.get() })
      return
    }

    const body = await readJsonBody(request)
    const value = await store.set(body && body.ids)
    writeJson(response, 200, { ok: true, value })
  }

  context.effect(() => {
    const disposers = [
      context.webServer.register({ kind: 'exact', path: '/fleet/stopped', handler }),
    ]

    return () => {
      for (const dispose of disposers.reverse()) dispose()
    }
  }, 'fleet-control: stopped-session store route')
}