import crypto from 'node:crypto'
import { createRemoteJWKSet, jwtVerify } from 'jose'

const SESSION_COOKIE = 'template_studio_session'
const FLOW_COOKIE = 'template_studio_oidc'
let jwks

function config() {
  return {
    issuer: process.env.KEYCLOAK_ISSUER?.replace(/\/$/, '') || '',
    clientId: process.env.KEYCLOAK_CLIENT_ID || '',
    clientSecret: process.env.KEYCLOAK_CLIENT_SECRET || '',
    baseUrl: process.env.APP_BASE_URL?.replace(/\/$/, '') || ''
  }
}

function authRequired() {
  return process.env.AUTH_REQUIRED !== 'false'
}

function parseCookies(req) {
  const values = {}
  for (const pair of String(req.headers.cookie || '').split(';')) {
    const index = pair.indexOf('=')
    if (index <= 0) continue
    values[pair.slice(0, index).trim()] = decodeURIComponent(pair.slice(index + 1).trim())
  }
  return values
}

function keyFor(purpose) {
  const { clientSecret } = config()
  if (!clientSecret) throw new Error('KEYCLOAK_CLIENT_SECRET is required')
  return crypto.createHash('sha256').update(`template-studio:${purpose}:${clientSecret}`).digest()
}

function pack(value, purpose) {
  const body = Buffer.from(JSON.stringify(value)).toString('base64url')
  const signature = crypto.createHmac('sha256', keyFor(purpose)).update(body).digest('base64url')
  return `${body}.${signature}`
}

function unpack(value, purpose) {
  if (!value) return null
  const [body, signature] = String(value).split('.')
  if (!body || !signature) return null
  const expected = crypto.createHmac('sha256', keyFor(purpose)).update(body).digest()
  const received = Buffer.from(signature, 'base64url')
  if (expected.length !== received.length || !crypto.timingSafeEqual(expected, received)) return null
  try {
    return JSON.parse(Buffer.from(body, 'base64url').toString('utf8'))
  } catch {
    return null
  }
}

function cookie(name, value, maxAge) {
  return `${name}=${encodeURIComponent(value)}; Path=/; HttpOnly; Secure; SameSite=Lax; Max-Age=${maxAge}`
}

function clearCookie(name) {
  return `${name}=; Path=/; HttpOnly; Secure; SameSite=Lax; Max-Age=0`
}

function redirectUri(req) {
  const { baseUrl } = config()
  if (baseUrl) return `${baseUrl}/auth/callback`
  const proto = req.headers['x-forwarded-proto'] || req.protocol || 'https'
  return `${proto}://${req.get('host')}/auth/callback`
}

function readSession(req) {
  if (!authRequired()) {
    return { sub: 'local-dev', preferred_username: 'local-dev', name: 'Local developer', exp: Math.floor(Date.now() / 1000) + 3600 }
  }
  const session = unpack(parseCookies(req)[SESSION_COOKIE], 'session')
  if (!session || Number(session.exp || 0) <= Math.floor(Date.now() / 1000)) return null
  return session
}

function ensureConfigured() {
  const { issuer, clientId, clientSecret } = config()
  if (!issuer || !clientId || !clientSecret) throw new Error('Keycloak OIDC is not fully configured')
}

export function registerAuthRoutes(app) {
  app.get('/auth/login', (req, res, next) => {
    try {
      if (!authRequired()) return res.redirect('/')
      ensureConfigured()
      const { issuer, clientId } = config()
      const state = crypto.randomBytes(24).toString('base64url')
      const nonce = crypto.randomBytes(24).toString('base64url')
      const verifier = crypto.randomBytes(48).toString('base64url')
      const challenge = crypto.createHash('sha256').update(verifier).digest('base64url')
      const flow = pack({ state, nonce, verifier, exp: Math.floor(Date.now() / 1000) + 600 }, 'oidc')
      res.setHeader('Set-Cookie', cookie(FLOW_COOKIE, flow, 600))

      const url = new URL(`${issuer}/protocol/openid-connect/auth`)
      url.search = new URLSearchParams({
        client_id: clientId,
        response_type: 'code',
        scope: 'openid profile email',
        redirect_uri: redirectUri(req),
        state,
        nonce,
        code_challenge: challenge,
        code_challenge_method: 'S256'
      }).toString()
      res.redirect(url.toString())
    } catch (error) {
      next(error)
    }
  })

  app.get('/auth/callback', async (req, res, next) => {
    try {
      ensureConfigured()
      const { issuer, clientId, clientSecret } = config()
      const flow = unpack(parseCookies(req)[FLOW_COOKIE], 'oidc')
      if (!flow || flow.exp <= Math.floor(Date.now() / 1000) || flow.state !== req.query.state || !req.query.code) {
        return res.status(400).send('Invalid or expired sign-in request.')
      }

      const tokenResponse = await fetch(`${issuer}/protocol/openid-connect/token`, {
        method: 'POST',
        headers: { 'content-type': 'application/x-www-form-urlencoded' },
        body: new URLSearchParams({
          grant_type: 'authorization_code',
          client_id: clientId,
          client_secret: clientSecret,
          redirect_uri: redirectUri(req),
          code: String(req.query.code),
          code_verifier: flow.verifier
        })
      })
      if (!tokenResponse.ok) throw new Error(`OIDC token exchange failed: ${tokenResponse.status}`)
      const tokens = await tokenResponse.json()
      if (!tokens.id_token) throw new Error('OIDC response did not contain an ID token')

      jwks ||= createRemoteJWKSet(new URL(`${issuer}/protocol/openid-connect/certs`))
      const { payload } = await jwtVerify(tokens.id_token, jwks, {
        issuer,
        audience: clientId
      })
      if (payload.nonce !== flow.nonce) throw new Error('OIDC nonce mismatch')

      const now = Math.floor(Date.now() / 1000)
      const session = {
        sub: payload.sub,
        preferred_username: payload.preferred_username || payload.email || payload.sub,
        email: payload.email,
        name: payload.name || payload.preferred_username || payload.email,
        exp: Math.min(Number(payload.exp || now + 8 * 3600), now + 8 * 3600)
      }
      res.setHeader('Set-Cookie', [
        cookie(SESSION_COOKIE, pack(session, 'session'), Math.max(1, session.exp - now)),
        clearCookie(FLOW_COOKIE)
      ])
      res.redirect('/')
    } catch (error) {
      next(error)
    }
  })

  app.get('/auth/logout', (_req, res) => {
    res.setHeader('Set-Cookie', clearCookie(SESSION_COOKIE))
    res.redirect('/')
  })

  app.get('/api/session', (req, res) => {
    const session = readSession(req)
    if (!session) return res.status(401).json({ authenticated: false })
    res.setHeader('Cache-Control', 'no-store')
    res.json({ authenticated: true, user: session })
  })
}

export function requireAuth(req, res, next) {
  try {
    const session = readSession(req)
    if (!session) return res.status(401).json({ error: 'authentication_required' })
    req.user = session
    next()
  } catch (error) {
    next(error)
  }
}