// GET /api/offline/mail?kind=mailboxes|list|message - the OFFLINE READ SURFACE.
//
// THIS ROUTE MUST NEVER MAKE A NETWORK CALL. That is the whole feature: it is
// consulted precisely when the backend is unreachable, so a JMAP session fetch to
// learn the account id would fail for the exact reason the route was called. The
// account is resolved from the request's own encrypted `jmap_stalwart_ctx` cookie
// (a local decrypt) and from the account ids the store already holds rows for.
//
// It is a FALLBACK, not a cache in front of the server - see `read.ts`'s header
// for the coherence rules that depend on that, and `lib/offline-fallback-client.ts`
// for the one place that decides a read has genuinely failed.
import { NextRequest, NextResponse } from 'next/server';
import {
  readEnvelopePage, readMailboxes, readMessage,
} from '@/lib/offline-replica/read';
import {
  resolveIndexSession, resolveReadAccountId, withReplica,
} from '@/lib/offline-replica/engine';
import { gateReplicaRoute, NO_STORE, replicaErrorResponse } from '@/lib/offline-replica/route-gate';

export const runtime = 'nodejs';
export const dynamic = 'force-dynamic';

const MAX_LIMIT = 200;

export async function GET(request: NextRequest) {
  const gated = gateReplicaRoute();
  if (gated) return gated;

  const params = request.nextUrl.searchParams;
  const kind = params.get('kind') ?? 'mailboxes';
  if (kind !== 'mailboxes' && kind !== 'list' && kind !== 'message') {
    return NextResponse.json({ error: 'kind must be mailboxes, list or message' }, { status: 400 });
  }

  try {
    const session = await resolveIndexSession(request);
    const payload = await withReplica(session.accountId, (store) => {
      const jmapAccountId = resolveReadAccountId(store, params.get('jmapAccountId'));
      if (!jmapAccountId) {
        // Nothing synced yet for this account. Not an error - the caller falls
        // back to whatever it would have shown without a replica.
        return { empty: true as const };
      }

      if (kind === 'mailboxes') {
        return { empty: false as const, jmapAccountId, mailboxes: readMailboxes(store, jmapAccountId) };
      }

      if (kind === 'list') {
        const rawLimit = Number(params.get('limit') ?? '50');
        const limit = Number.isFinite(rawLimit)
          ? Math.min(Math.max(Math.trunc(rawLimit), 1), MAX_LIMIT)
          : 50;
        const rawOffset = Number(params.get('offset') ?? '0');
        const offset = Number.isFinite(rawOffset) ? Math.max(Math.trunc(rawOffset), 0) : 0;
        // An absent mailboxId means "everything", which is what the unified views
        // ask for; an empty string is a caller bug and must not silently widen.
        const mailboxParam = params.get('mailboxId');
        const mailboxId = mailboxParam === null ? null : mailboxParam;
        if (mailboxId === '') {
          return { empty: true as const };
        }
        const page = readEnvelopePage(store, jmapAccountId, mailboxId, limit, offset);
        return { empty: false as const, jmapAccountId, ...page };
      }

      const id = params.get('id');
      if (!id || id.length > 256) return { empty: true as const };
      const message = readMessage(store, jmapAccountId, id);
      if (!message) return { empty: false as const, jmapAccountId, email: null, hasBody: false };
      return {
        empty: false as const,
        jmapAccountId,
        email: message.email,
        hasBody: message.hasBody,
      };
    });

    if (payload.empty) {
      return NextResponse.json({ ok: true, available: false }, { headers: NO_STORE });
    }
    return NextResponse.json({ ok: true, available: true, ...payload }, { headers: NO_STORE });
  } catch (error) {
    return replicaErrorResponse(error, 'offline read');
  }
}