chronus/src/utils/invoice.ts

import { db } from "../db";
import { invoices, invoiceItems } from "../db/schema";
import { eq } from "drizzle-orm";

/**
 * Recalculates the subtotal, tax amount, and total for a specific invoice
 * based on its items and tax rate.
 */
export async function recalculateInvoiceTotals(invoiceId: string) {
  // Fetch invoice to get tax rate
  const invoice = await db
    .select()
    .from(invoices)
    .where(eq(invoices.id, invoiceId))
    .get();

  if (!invoice) return;

  // Fetch all items
  const items = await db
    .select()
    .from(invoiceItems)
    .where(eq(invoiceItems.invoiceId, invoiceId))
    .all();

  // Calculate totals
  // Note: amounts are in cents
  const subtotal = items.reduce((acc, item) => acc + item.amount, 0);

  // Calculate discount
  const discountType = invoice.discountType || "percentage";
  const discountValue = invoice.discountValue || 0;
  let discountAmount = 0;

  if (discountType === "percentage") {
    discountAmount = Math.round(subtotal * (discountValue / 100));
  } else {
    // Fixed amount is assumed to be in cents
    discountAmount = Math.round(discountValue);
  }

  // Ensure discount doesn't exceed subtotal
  discountAmount = Math.max(0, Math.min(discountAmount, subtotal));

  const taxableAmount = subtotal - discountAmount;

  const taxRate = invoice.taxRate || 0;
  const taxAmount = Math.round(taxableAmount * (taxRate / 100));

  const total = taxableAmount + taxAmount;

  // Update invoice
  await db
    .update(invoices)
    .set({
      subtotal,
      discountAmount,
      taxAmount,
      total,
    })
    .where(eq(invoices.id, invoiceId));
}