// ── SSO (OAuth2 / OIDC) controller ─────────────────────────────────────────
//
// Drives the redirect flow for built-in (Google, Discord) and custom providers:
//   GET /auth/providers            → public discovery (enabled + valid providers)
//   GET /auth/sso/:provider/start  → begin login (redirect to the IdP)
//   GET /auth/sso/:provider/link   → begin account linking (requireAuth)
//   GET /auth/sso/:provider/callback → exchange code, then log in OR link
//
// LINK-ONLY policy: a login succeeds only if the external identity is already
// linked to an internal account. Unknown identities are refused, never
// auto-provisioned. Every successful login goes through sessionService, so the
// resulting session is identical to a local login (same cookie, logging, RBAC).

const users = require('../../../model/users/users.model')
const activity = require('../../../model/activity/activity.model')
const authProviders = require('../../../model/authProviders/authProviders.model')
const userIdentities = require('../../../model/userIdentities/userIdentities.model')
const registry = require('../../../auth/providers/registry')
const sessionService = require('../../../auth/session.service')
const ssoState = require('../../../auth/ssoState')
const token = require('../../../auth/token')

const log = require('../../../utils/logger')('sso')

const PROVIDER_ID_RE = /^[a-z0-9-]+$/

// Redirect targets (front-end routes). Errors surface as a query param the login
// / account pages can render.
const loginError = (code) => `/admin/login?sso_error=${code}`
const accountError = (code) => `/admin/account?link_error=${code}`

// Only allow returning to an internal /admin path (prevents open redirect).
function sanitizeReturn(returnTo) {
  if (typeof returnTo === 'string' && /^\/admin(?:[/?]|$)/.test(returnTo) && !returnTo.startsWith('//')) {
    return returnTo
  }
  return null
}

// Public base URL used to build the OAuth redirect_uri. Prefer APP_BASE_URL;
// fall back to the request's own origin with a warning if it is unset.
function appBaseUrl(req) {
  const configured = process.env.APP_BASE_URL
  if (configured) return configured.replace(/\/+$/, '')
  const derived = `${req.protocol}://${req.get('host')}`
  log.warn('APP_BASE_URL not set — deriving redirect_uri from the request', { derived })
  return derived
}
function redirectUriFor(req, providerId) {
  return `${appBaseUrl(req)}/api/v1/auth/sso/${providerId}/callback`
}

// httpOnly cookie carrying the signed tx (nonce + PKCE verifier + mode). Reuse the
// app's standard cookie options (httpOnly, sameSite=lax, secure=auto) + a TTL.
function txCookieOptions(req) {
  return { ...token.cookieOptions(req), maxAge: 10 * 60 * 1000 }
}

// GET /auth/providers — public discovery. Never touches secrets.
async function listProviders(req, res) {
  try {
    return res.json(await registry.listEnabledValid())
  } catch (err) {
    log.error('listProviders', err)
    return res.status(500).json({ message: 'Internal Server Error' })
  }
}

// Shared start for both login and link. `mode` ∈ 'login' | 'link'. For link,
// requireAuth has already run so req.user is the account to attach the identity to.
async function beginFlow(req, res, mode) {
  const providerId = req.params.provider
  const failUrl = mode === 'link' ? accountError('error') : loginError('error')
  try {
    if (!PROVIDER_ID_RE.test(providerId)) return res.redirect(failUrl)
    const row = await authProviders.getWithSecret(providerId)
    if (!row || !row.enabled || !registry.validateConfig(row).valid) {
      log.warn('sso start: provider unavailable', { provider: providerId, mode })
      return res.redirect(mode === 'link' ? accountError('unavailable') : loginError('unavailable'))
    }
    const provider = registry.instantiate(row)
    const tx = ssoState.createTx({
      provider: providerId,
      mode,
      linkUserId: mode === 'link' ? req.user.id : undefined,
      returnTo: sanitizeReturn(req.query.returnTo) || undefined,
    })
    res.cookie(ssoState.TX_COOKIE, tx.txToken, txCookieOptions(req))
    const url = provider.getAuthorizationUrl(tx.nonce, {
      redirectUri: redirectUriFor(req, providerId),
      codeChallenge: tx.codeChallenge,
    })
    return res.redirect(url)
  } catch (err) {
    log.error('sso start', err)
    return res.redirect(failUrl)
  }
}

const start = (req, res) => beginFlow(req, res, 'login')
const linkStart = (req, res) => beginFlow(req, res, 'link')

// GET /auth/sso/:provider/callback
async function callback(req, res) {
  const providerId = req.params.provider
  const txToken = req.cookies && req.cookies[ssoState.TX_COOKIE]
  const { code, state, error: oauthError } = req.query
  // The tx cookie is single-use — clear it no matter the outcome.
  res.clearCookie(ssoState.TX_COOKIE, token.cookieOptions(req))

  if (oauthError) {
    log.warn('sso callback: provider returned error', { provider: providerId, error: String(oauthError).slice(0, 60) })
    return res.redirect(loginError('denied'))
  }
  const tx = ssoState.verifyTx(txToken, state)
  if (!tx || tx.provider !== providerId || !code) {
    log.warn('sso callback: bad state', { provider: providerId })
    return res.redirect(loginError('bad_state'))
  }

  try {
    const row = await authProviders.getWithSecret(providerId)
    if (!row || !row.enabled || !registry.validateConfig(row).valid) {
      return res.redirect(loginError('unavailable'))
    }
    const provider = registry.instantiate(row)
    const profile = await provider.handleCallback({
      code,
      redirectUri: redirectUriFor(req, providerId),
      codeVerifier: tx.verifier,
    })
    if (tx.mode === 'link') return finishLink(req, res, providerId, tx, profile)
    return finishLogin(req, res, providerId, row.kind, tx, profile)
  } catch (err) {
    log.error('sso callback', err)
    return res.redirect(loginError('error'))
  }
}

// Link-only login: require an existing (provider, subject) identity → session.
async function finishLogin(req, res, providerId, kind, tx, profile) {
  const identity = await userIdentities.findByProviderSubject(providerId, profile.subject)
  if (!identity) {
    log.warn('sso login refused: no linked account', { provider: providerId })
    return res.redirect(loginError('not_linked'))
  }
  const user = await users.getById(identity.user_id)
  if (!user) return res.redirect(loginError('not_linked'))

  const authMethod = sessionService.AUTH_METHODS.includes(kind) ? kind : 'sso'
  const { token: sessionToken } = sessionService.createSession(user, authMethod)
  token.setAuthCookie(req, res, sessionToken)
  await users.recordLogin(user.id)
  await activity.log({ req, userId: user.id, action: 'auth.sso.login', detail: { provider: providerId } })
  log.info('sso login success', { provider: providerId, id: user.id, ip: req.ip })
  return res.redirect(sanitizeReturn(tx.returnTo) || '/admin')
}

// Attach the external identity to the account that initiated linking (tx.linkUserId
// was captured behind requireAuth at /link start, so the signed tx authorizes it).
async function finishLink(req, res, providerId, tx, profile) {
  const userId = tx.linkUserId
  if (!userId) return res.redirect(loginError('error'))
  const existing = await userIdentities.findByProviderSubject(providerId, profile.subject)
  if (existing && existing.user_id !== userId) {
    return res.redirect(accountError('in_use')) // that external identity belongs to another account
  }
  if (!existing) {
    await userIdentities.link({ userId, provider: providerId, subject: profile.subject, email: profile.email })
    await activity.log({ req, userId, action: 'auth.sso.link', detail: { provider: providerId } })
    log.info('sso account linked', { provider: providerId, userId })
  }
  return res.redirect(`/admin/account?linked=${providerId}`)
}

module.exports = { listProviders, start, linkStart, callback, beginFlow, finishLogin, finishLink }