/**
 * Mobile auth helper — validates Bearer token and returns userId
 * Token format: base64url(userId:timestamp:hmac)
 */
import { createHmac, timingSafeEqual } from 'crypto'

function getSecret(): string {
  const secret = process.env.NEXTAUTH_SECRET
  if (!secret) {
    throw new Error('NEXTAUTH_SECRET is required for mobile auth')
  }
  return secret
}

export function createMobileToken(userId: string): string {
  const ts = Date.now()
  const payload = `${userId}:${ts}`
  const sig = createHmac('sha256', getSecret()).update(payload).digest('hex')
  return Buffer.from(`${payload}:${sig}`).toString('base64url')
}

export function verifyMobileToken(token: string): string | null {
  try {
    const decoded = Buffer.from(token, 'base64url').toString('utf-8')
    const lastColon = decoded.lastIndexOf(':')
    if (lastColon === -1) return null
    const sig = decoded.slice(lastColon + 1)
    const payload = decoded.slice(0, lastColon)
    const secondColon = payload.lastIndexOf(':')
    if (secondColon === -1) return null
    const userId = payload.slice(0, secondColon)
    const ts = payload.slice(secondColon + 1)
    const expected = createHmac('sha256', getSecret()).update(payload).digest('hex')
    const sigBuf = Buffer.from(sig)
    const expectedBuf = Buffer.from(expected)
    if (sigBuf.length !== expectedBuf.length || !timingSafeEqual(sigBuf, expectedBuf)) return null
    if (Date.now() - Number(ts) > 90 * 24 * 60 * 60 * 1000) return null
    return userId
  } catch {
    return null
  }
}

export function getMobileUserId(request: Request): string | null {
  const auth = request.headers.get('Authorization')
  if (!auth?.startsWith('Bearer ')) return null
  return verifyMobileToken(auth.slice(7))
}