import crypto from 'node:crypto'
import fs from 'node:fs'
import path from 'node:path'
import { fileURLToPath } from 'node:url'
import { signSession, verifySession, parseCookies } from './util.js'
import { sessionSecret } from './store.js'

const __an_dirname = path.dirname(fileURLToPath(import.meta.url))
export const BUILD_ID = (() => {
  try {
    return fs.readFileSync(path.join(__an_dirname, '..', 'public', 'build-id'), 'utf8').trim() || 'dev'
  } catch {
    return 'dev'
  }
})()

const SECRET = sessionSecret()
const PROVIDER = process.env.OPENID_PROVIDER_URL || 'https://huggingface.co'
const CLIENT_ID = process.env.OAUTH_CLIENT_ID
const CLIENT_SECRET = process.env.OAUTH_CLIENT_SECRET
export const OAUTH_ENABLED = Boolean(CLIENT_ID && CLIENT_SECRET)
export const HOST = process.env.SPACE_HOST
  ? `https://${process.env.SPACE_HOST}`
  : `http://localhost:${process.env.PORT || 3000}`

const COOKIE = 'ie_session'

export function sessionFromCookieHeader(cookieHeader) {
  const cookies = parseCookies(cookieHeader)
  const session = verifySession(cookies[COOKIE], SECRET)
  if (session?.u) return { username: session.u, name: session.n || session.u, avatar: session.p || null }
  return null
}

// --- HF token -> username (agents authenticate with a personal HF token) ---

const tokenCache = new Map() // token -> { user, exp }

export async function userFromToken(token) {
  if (!token) return null
  if (!OAUTH_ENABLED && token.startsWith('dev:')) {
    const u = token.slice(4)
    return u ? { username: u, name: u, avatar: null } : null
  }
  const cached = tokenCache.get(token)
  if (cached && cached.exp > Date.now()) return cached.user
  try {
    const res = await fetch('https://huggingface.co/api/whoami-v2', {
      headers: { authorization: `Bearer ${token}` },
    })
    if (!res.ok) return null
    const body = await res.json()
    if (!body?.name) return null
    const user = { username: body.name, name: body.fullname || body.name, avatar: body.avatarUrl || null }
    tokenCache.set(token, { user, exp: Date.now() + 5 * 60 * 1000 })
    return user
  } catch {
    return null
  }
}

export function bearerFromRequest(req) {
  const auth = req.headers['authorization']
  if (auth?.startsWith('Bearer ')) return auth.slice(7)
  if (req.headers['x-hf-token']) return req.headers['x-hf-token']
  return null
}

// Express middleware: resolves req.user from session cookie, app-issued agent
// key (Bearer ak_...), or HF token. Agent keys also set req.agent = { handle }.
export function resolveUser() {
  return async (req, res, next) => {
    const session = sessionFromCookieHeader(req.headers.cookie)
    if (session) {
      req.user = session
      return next()
    }
    const bearer = bearerFromRequest(req)
    if (bearer?.startsWith('ak_')) {
      const { agentByKey } = await import('./store.js')
      const agent = agentByKey(bearer)
      if (agent) {
        req.user = { username: agent.owner, name: agent.owner, avatar: null }
        req.agent = { handle: agent.handle }
      }
      return next()
    }
    req.user = await userFromToken(bearer)
    next()
  }
}

// Some routes are for humans only (accepting suggestions, creating docs, sharing…)
export function requireHuman(req, res, next) {
  if (req.agent) return res.status(403).json({ error: 'agent keys cannot perform this action — it requires a signed-in human' })
  next()
}

// The Space owner is the instance admin (SPACE_AUTHOR_NAME is set by HF Spaces).
const ADMIN_USER = process.env.SPACE_AUTHOR_NAME || process.env.ADMIN_USER || null

export function isAdmin(username) {
  return Boolean(ADMIN_USER && username === ADMIN_USER)
}

export function requireUser(req, res, next) {
  if (!req.user) return res.status(401).json({ error: 'authentication required (sign in, or pass an HF token as Authorization: Bearer)' })
  next()
}

// --- routes ---

export function registerAuthRoutes(app) {
  app.get('/api/me', (req, res) => {
    res.json({ user: req.user || null, oauth: OAUTH_ENABLED, is_admin: req.user ? isAdmin(req.user.username) : false, build_id: BUILD_ID })
  })

  app.get('/auth/logout', (req, res) => {
    res.setHeader('set-cookie', `${COOKIE}=; Path=/; Max-Age=0;${cookieFlags()}`)
    res.redirect('/')
  })

  if (!OAUTH_ENABLED) {
    // Dev-only login: /auth/dev?u=alice
    app.get('/auth/dev', (req, res) => {
      const u = String(req.query.u || '').trim()
      if (!/^[a-zA-Z0-9_.-]{1,40}$/.test(u)) return res.status(400).send('bad username')
      setSessionCookie(res, { u, n: u, p: null })
      res.redirect(String(req.query.next || '/'))
    })
    app.get('/auth/login', (req, res) => {
      res.redirect('/auth/dev?u=dev-user&next=' + encodeURIComponent(String(req.query.next || '/')))
    })
    return
  }

  // CSRF state lives server-side (like tfrere/research-article-template-editor):
  // a state cookie would be third-party inside the huggingface.co iframe and
  // silently dropped by the browser, breaking the callback check.
  const pendingStates = new Map() // state -> { ts, next }
  const cleanupStates = () => {
    const now = Date.now()
    for (const [state, v] of pendingStates) {
      if (now - v.ts > 10 * 60 * 1000) pendingStates.delete(state)
    }
  }

  app.get('/auth/login', (req, res) => {
    cleanupStates()
    const state = crypto.randomBytes(16).toString('hex')
    pendingStates.set(state, { ts: Date.now(), next: safeNext(req.query.next) })
    const url = new URL(`${PROVIDER}/oauth/authorize`)
    url.searchParams.set('client_id', CLIENT_ID)
    url.searchParams.set('redirect_uri', `${HOST}/auth/callback`)
    url.searchParams.set('response_type', 'code')
    url.searchParams.set('scope', 'openid profile')
    url.searchParams.set('state', state)
    res.redirect(url.toString())
  })

  app.get('/auth/callback', async (req, res) => {
    try {
      const state = String(req.query.state || '')
      const pending = pendingStates.get(state)
      if (!req.query.code || !pending) {
        return res.status(400).send('Sign-in session expired or unknown — please go back and sign in again.')
      }
      pendingStates.delete(state)
      const tokenRes = await fetch(`${PROVIDER}/oauth/token`, {
        method: 'POST',
        headers: { 'content-type': 'application/x-www-form-urlencoded' },
        body: new URLSearchParams({
          grant_type: 'authorization_code',
          code: String(req.query.code || ''),
          redirect_uri: `${HOST}/auth/callback`,
          client_id: CLIENT_ID,
          client_secret: CLIENT_SECRET,
        }),
      })
      if (!tokenRes.ok) return res.status(502).send('token exchange failed: ' + (await tokenRes.text()).slice(0, 200))
      const { access_token } = await tokenRes.json()
      const infoRes = await fetch(`${PROVIDER}/oauth/userinfo`, { headers: { authorization: `Bearer ${access_token}` } })
      if (!infoRes.ok) return res.status(502).send('userinfo failed')
      const info = await infoRes.json()
      const username = info.preferred_username || info.sub
      setSessionCookie(res, { u: username, n: info.name || username, p: info.picture || null })
      res.redirect(pending.next || '/')
    } catch (err) {
      res.status(500).send('auth error: ' + err.message)
    }
  })
}

function safeNext(next) {
  const s = String(next || '/')
  return s.startsWith('/') && !s.startsWith('//') ? s : '/'
}

function setSessionCookie(res, payload) {
  const value = signSession(payload, SECRET)
  res.setHeader('set-cookie', `${COOKIE}=${value}; Path=/; Max-Age=${30 * 24 * 3600};${cookieFlags()}`)
}

// The Space is often used embedded in an iframe on huggingface.co, where the app
// origin (hf.space) is cross-site: SameSite=Lax cookies are never sent there.
// SameSite=None lets the session cookie work embedded.
function cookieFlags() {
  return OAUTH_ENABLED ? ' HttpOnly; SameSite=None; Secure' : ' HttpOnly; SameSite=Lax'
}