import { NextResponse } from 'next/server'
import { authenticateUser, seedAdminIfEmpty } from '@/lib/users'
import { createSession } from '@/lib/session'

// ── In-memory rate limiter (single-instance, resets on restart) ──────────────
interface RateLimitEntry {
  attempts: number
  lockedUntil: number
}
const rateLimitMap = new Map<string, RateLimitEntry>()
const MAX_ATTEMPTS = 5
const LOCKOUT_MS = 15 * 60 * 1000 // 15 minutes

function getClientIp(req: Request): string {
  return (
    req.headers.get('x-forwarded-for')?.split(',')[0].trim() ??
    req.headers.get('x-real-ip') ??
    'unknown'
  )
}

function checkRateLimit(ip: string): { allowed: boolean; retryAfterSecs?: number } {
  const now = Date.now()
  const entry = rateLimitMap.get(ip)
  if (!entry) return { allowed: true }
  if (entry.lockedUntil > now) {
    return { allowed: false, retryAfterSecs: Math.ceil((entry.lockedUntil - now) / 1000) }
  }
  // Lock has expired — reset
  rateLimitMap.delete(ip)
  return { allowed: true }
}

function recordFailedAttempt(ip: string): void {
  const now = Date.now()
  const entry = rateLimitMap.get(ip) ?? { attempts: 0, lockedUntil: 0 }
  entry.attempts++
  if (entry.attempts >= MAX_ATTEMPTS) {
    entry.lockedUntil = now + LOCKOUT_MS
    entry.attempts = 0
  }
  rateLimitMap.set(ip, entry)
}

function clearAttempts(ip: string): void {
  rateLimitMap.delete(ip)
}

// ── Handler ───────────────────────────────────────────────────────────────────
export async function POST(request: Request) {
  const ip = getClientIp(request)
  const { allowed, retryAfterSecs } = checkRateLimit(ip)

  if (!allowed) {
    return NextResponse.json(
      { error: `Too many attempts. Try again in ${retryAfterSecs} seconds.` },
      {
        status: 429,
        headers: { 'Retry-After': String(retryAfterSecs) },
      },
    )
  }

  let body: { username?: string; password?: string }
  try {
    body = (await request.json()) as { username?: string; password?: string }
  } catch {
    return NextResponse.json({ error: 'Invalid JSON' }, { status: 400 })
  }

  const username = String(body.username ?? '').trim()
  const password = String(body.password ?? '')

  if (!username || !password) {
    return NextResponse.json({ error: 'Username and password are required' }, { status: 400 })
  }

  // Seed admin on first login attempt if no users exist yet
  await seedAdminIfEmpty()

  const user = await authenticateUser(username, password)
  if (!user) {
    recordFailedAttempt(ip)
    // Return generic error — don't reveal whether the username exists
    return NextResponse.json({ error: 'Invalid username or password' }, { status: 401 })
  }

  clearAttempts(ip)
  await createSession({ userId: user.id, username: user.username, role: user.role })
  return NextResponse.json({ ok: true, username: user.username, role: user.role })
}