import { NextResponse } from "next/server"

// ============================================================================
// Fixed-window rate limiting for endpoints Better Auth does not cover.
//
// Better Auth throttles its own /api/auth/* endpoints (see lib/auth.ts). Nothing
// else was limited: the public v1 API, uploads, and the unauthenticated tenant
// portal maintenance submission were all unbounded. This closes that gap.
//
// SCOPE / LIMITATION: counters live in the process, so the limit is enforced
// PER INSTANCE. On a single container (the current Dokploy deployment) that is
// the real limit; if the app is ever scaled horizontally, an attacker's
// effective ceiling multiplies by the replica count. That is still a bounded,
// large improvement over "no limit at all", and the swap to a shared store
// (Postgres or Redis) only has to replace `hit()` below. Do NOT let the absence
// of a shared store be a reason to ship no limit.
// ============================================================================

type Counter = { count: number; resetAt: number }

const buckets = new Map<string, Counter>()

// Drop expired counters so a long-lived process doesn't accumulate a key per
// distinct IP forever. Runs opportunistically on write, not on a timer.
let lastSweep = 0
function sweep(now: number): void {
  if (now - lastSweep < 60_000) return
  lastSweep = now
  for (const [key, c] of buckets) {
    if (c.resetAt <= now) buckets.delete(key)
  }
}

export type RateLimitResult = {
  ok: boolean
  /** Requests remaining in the current window. */
  remaining: number
  /** Seconds until the window resets — sent as Retry-After on a 429. */
  retryAfter: number
  limit: number
}

/**
 * Record a hit against `key` and report whether it is within `limit` per
 * `windowSeconds`. Callers pass a namespaced key (e.g. `v1:<userId>`) so
 * different endpoints never share a bucket.
 */
export function hit(key: string, limit: number, windowSeconds: number): RateLimitResult {
  const now = Date.now()
  sweep(now)

  const existing = buckets.get(key)
  if (!existing || existing.resetAt <= now) {
    const resetAt = now + windowSeconds * 1000
    buckets.set(key, { count: 1, resetAt })
    return { ok: true, remaining: limit - 1, retryAfter: windowSeconds, limit }
  }

  existing.count++
  const retryAfter = Math.max(1, Math.ceil((existing.resetAt - now) / 1000))
  return {
    ok: existing.count <= limit,
    remaining: Math.max(0, limit - existing.count),
    retryAfter,
    limit,
  }
}

/**
 * The caller's IP, taken from the proxy headers Traefik/Dokploy set. Falls back
 * to a constant so a missing header degrades to one shared bucket (fail closed
 * on volume) rather than to no limit at all.
 */
export function clientIp(request: Request): string {
  const fwd = request.headers.get("x-forwarded-for")?.split(",")[0]?.trim()
  return fwd || request.headers.get("x-real-ip") || "unknown"
}

/** Standard 429 with rate-limit headers, or null when the request is allowed. */
export function rateLimitResponse(result: RateLimitResult): NextResponse | null {
  if (result.ok) return null
  return NextResponse.json(
    { error: "Too many requests. Please slow down and try again shortly." },
    {
      status: 429,
      headers: {
        "Retry-After": String(result.retryAfter),
        "X-RateLimit-Limit": String(result.limit),
        "X-RateLimit-Remaining": "0",
      },
    }
  )
}

/**
 * Convenience wrapper: hit the bucket and return a ready 429 if over the limit.
 *
 *   const limited = enforceRateLimit(`upload:${ownerId}`, 30, 60)
 *   if (limited) return limited
 */
export function enforceRateLimit(
  key: string,
  limit: number,
  windowSeconds: number
): NextResponse | null {
  return rateLimitResponse(hit(key, limit, windowSeconds))
}