import { NextResponse } from "next/server";
import { getSessionUser } from "@/lib/session";
import { computeInvoiceDraft } from "@/lib/billing";
import { listInvoices } from "@/lib/db";

/**
 * GET /api/billing/current
 *
 * Running total for the current calendar month — what the
 * customer will be billed if no further activity happens. Uses
 * the same compute pipeline as the final invoice (LiteLLM spend,
 * Threema usage, skill day-counting, proration) so the number
 * the customer sees matches what they'll eventually receive
 * within the limits of intra-month drift.
 *
 * If an invoice has ALREADY been issued for the current month
 * (e.g. cron ran early, admin manually generated), we return
 * that issued invoice instead — no point showing a draft that
 * duplicates a real invoice.
 *
 * Returns:
 *   { issued: Invoice }           // current-month invoice exists
 *   { draft: InvoiceDraft }       // still accruing
 *   { error: ... }                // org missing billing config
 *
 * Cost: 1 LiteLLM HTTP call + 1 Threema HTTP call + a handful of
 * DB queries per skill. Sub-second typically. No caching; called
 * on demand from the customer billing page.
 */
export async function GET() {
  const user = await getSessionUser();
  if (!user) {
    return NextResponse.json({ error: "Unauthorized" }, { status: 401 });
  }
  // Resolve current calendar month from UTC. Billing is UTC-day
  // based throughout (see billing.ts iterDays comment), so the
  // running total inherits that same semantics.
  const now = new Date();
  const year = now.getUTCFullYear();
  const month = now.getUTCMonth() + 1; // 1-12
  const periodMonth = `${year}-${String(month).padStart(2, "0")}`;

  // 1. Has the current month already been invoiced?
  const existing = await listInvoices({
    zitadelOrgId: user.orgId,
    periodMonth,
    limit: 1,
  });
  if (existing.length > 0) {
    return NextResponse.json({ issued: existing[0] });
  }

  // 2. Otherwise compute the draft. Falls through to error if the
  //    org doesn't have a billing config yet (no Address on file).
  try {
    const draft = await computeInvoiceDraft({
      zitadelOrgId: user.orgId,
      year,
      month,
    });
    return NextResponse.json({ draft });
  } catch (e: any) {
    // Most likely: org_billing row missing. We surface a 200 with a
    // soft error code rather than 500 — the customer-side widget
    // displays a helpful "complete your billing details" message
    // instead of a stack trace.
    return NextResponse.json(
      {
        error: e?.message ?? "Could not compute running total.",
        code: e?.code ?? "COMPUTE_FAILED",
      },
      { status: 200 }
    );
  }
}