/**
 * Webhook endpoint — receives album update events from Immich and
 * invalidates the corresponding in-memory cache entries.
 *
 * Security: requests must include an HMAC-SHA256 signature in the
 * `x-immich-signature` header, computed as:
 *
 *   HMAC-SHA256(WEBHOOK_SECRET, raw request body)
 *
 * If WEBHOOK_SECRET is not set, the endpoint returns 501. Bodies over
 * MAX_BODY_BYTES are refused with 413 before the signature is checked.
 *
 * Supported Immich event types:
 *   - album.updated      → invalidates the specific album
 *   - album.assetAdded   → invalidates the specific album
 *   - album.assetRemoved → invalidates the specific album
 *   - *                  → any other event clears the full cache
 *
 * POST /api/webhook
 */

import { NextRequest, NextResponse } from 'next/server';
import { createHmac, timingSafeEqual } from 'crypto';
import { immich } from '@/lib/immich';
import { env } from '@/lib/env';
import { checkRateLimit, getClientIp } from '@/lib/rate-limit';
import { readBytesCapped } from '@/lib/requestBody';

// Tight rate limit — webhooks should come from one trusted source only
const WEBHOOK_RPM = 60;

/**
 * Largest body the route reads before the signature is checked. The payload
 * is a small JSON object (`{ "event": "album.updated", "albumId": "<uuid>" }`,
 * well under 1 KiB), so 64 KiB leaves ample headroom for extra fields while
 * keeping an unauthenticated sender from making the server buffer and hash
 * an arbitrarily large body.
 */
const MAX_BODY_BYTES = 64 * 1024;

/** An HMAC-SHA256 hex digest: exactly 64 hex characters. */
const SIGNATURE_PATTERN = /^[0-9a-f]{64}$/i;

/** Album-scoped Immich webhook events. */
const ALBUM_EVENTS = new Set(['album.updated', 'album.assetAdded', 'album.assetRemoved']);

export async function POST(request: NextRequest) {
  // ── Feature guard ──────────────────────────────────
  if (!env.WEBHOOK_SECRET) {
    return NextResponse.json(
      { error: 'Webhook is not configured. Set WEBHOOK_SECRET in your environment.' },
      { status: 501 },
    );
  }

  // ── Rate limiting ──────────────────────────────────
  const ip = getClientIp(request);
  const { success } = checkRateLimit(`webhook:${ip}`, WEBHOOK_RPM);
  if (!success) {
    return NextResponse.json({ error: 'Too many requests' }, { status: 429 });
  }

  // ── Body size ──────────────────────────────────────
  // The declared length is refused before a byte is read; the capped reader
  // covers a missing or understated Content-Length and chunked bodies.
  const declared = Number(request.headers.get('content-length') ?? '');
  if (Number.isFinite(declared) && declared > MAX_BODY_BYTES) {
    return NextResponse.json({ error: 'Payload too large' }, { status: 413 });
  }

  // ── Read body (needed for HMAC verification) ───────
  let rawBody: Buffer | null;
  try {
    rawBody = await readBytesCapped(request, MAX_BODY_BYTES);
  } catch {
    return NextResponse.json({ error: 'Failed to read request body' }, { status: 400 });
  }
  if (rawBody === null) {
    return NextResponse.json({ error: 'Payload too large' }, { status: 413 });
  }

  // ── Signature verification ─────────────────────────
  const signature = request.headers.get('x-immich-signature');
  if (!signature) {
    console.warn('[Webhook] ⚠️ Missing x-immich-signature header');
    return NextResponse.json({ error: 'Missing signature' }, { status: 401 });
  }

  const expected = createHmac('sha256', env.WEBHOOK_SECRET).update(rawBody).digest('hex');

  // Anything but a 64-character hex digest is refused before decoding, so a
  // malformed or over-long header gets the same answer as a wrong one.
  const signatureValid =
    SIGNATURE_PATTERN.test(signature) &&
    timingSafeEqual(Buffer.from(signature, 'hex'), Buffer.from(expected, 'hex'));

  if (!signatureValid) {
    console.warn(`[Webhook] ⚠️ Invalid signature from ${ip}`);
    return NextResponse.json({ error: 'Invalid signature' }, { status: 401 });
  }

  // ── Parse payload ──────────────────────────────────
  let payload: { event?: string; albumId?: string } = {};
  try {
    payload = JSON.parse(new TextDecoder().decode(rawBody));
  } catch {
    return NextResponse.json({ error: 'Invalid JSON payload' }, { status: 400 });
  }

  const { event, albumId } = payload;

  if (!event) {
    return NextResponse.json({ error: 'Missing event field in payload' }, { status: 400 });
  }

  // ── Cache invalidation ─────────────────────────────
  if (ALBUM_EVENTS.has(event) && albumId && typeof albumId === 'string') {
    immich.invalidateAlbum(albumId);
    return NextResponse.json({ ok: true, invalidated: albumId });
  }

  // Any unrecognised event → full cache clear
  immich.invalidateAll();
  return NextResponse.json({ ok: true, invalidated: 'all' });
}