import type { BankAccount, Invoice, InvoiceItem, Settings, TaxType } from "./types";
import { computeLineAmount, computeTotals } from "./invoice";
import { amountInWords } from "./numberToWords";

/** The form fields the preview reads. */
export interface PreviewForm {
  invoiceDate: string;
  dueDate: string;
  clientId: number | null;
  clientName: string;
  clientAddress: string;
  clientGstin: string;
  poNumber: string;
  placeOfSupply: string;
  discount: number;
  taxRate: number;
  reverseCharge: boolean;
  signaturePath: string | null;
  notes: string;
  items: InvoiceItem[];
}

/**
 * The tax treatment Rust derives from the supplier state and the place of supply
 * (src-tauri/src/gst.rs); the form shows and sends the same value.
 */
export function deriveTaxType(settings: Settings, placeOfSupply: string): TaxType {
  if (settings.gstRegistration === "unregistered") return "none";
  return !placeOfSupply || placeOfSupply === settings.vendorStateCode ? "cgst_sgst" : "igst";
}

/** Mirrors vendor_snapshot() in src-tauri/src/commands/invoice.rs. */
export function vendorSnapshotJson(settings: Settings): string {
  return JSON.stringify({
    vendorName: settings.vendorName,
    vendorAddress: settings.vendorAddress,
    vendorEmail: settings.vendorEmail,
    vendorPhone: settings.vendorPhone,
    vendorPan: settings.vendorPan,
    vendorGstin: settings.gstRegistration === "unregistered" ? "" : settings.vendorGstin.trim(),
    vendorStateCode: settings.vendorStateCode,
    logoPath: settings.logoPath,
    logoKnockoutPath: settings.logoKnockoutPath,
    logoMeta: settings.logoMeta,
    logoIncludesName: settings.logoIncludesName,
    signaturePath: settings.signaturePath,
    gstRegistration: settings.gstRegistration,
    signatoryName: settings.signatoryName,
    signatoryDesignation: settings.signatoryDesignation,
  });
}

/**
 * A draft-status Invoice built from the live form, so the real renderer can draw it before anything
 * is issued. Totals use the same paise rounding Rust stores. `number` is the next number (a peek),
 * not yet consumed.
 */
export function formToPreviewInvoice(form: PreviewForm, number: string, settings: Settings, bank: BankAccount | null): Invoice {
  const taxType = deriveTaxType(settings, form.placeOfSupply);
  const registered = settings.gstRegistration !== "unregistered";
  const totals = computeTotals(form.items, form.discount, taxType, form.taxRate);
  const items = form.items.map((item, i) => ({ ...item, amount: computeLineAmount(item), sortOrder: i }));
  return {
    id: 0,
    number,
    seriesId: null,
    invoiceDate: form.invoiceDate,
    dueDate: form.dueDate,
    clientId: form.clientId,
    clientName: form.clientName,
    clientAddress: form.clientAddress,
    clientGstin: form.clientGstin,
    poNumber: form.poNumber,
    placeOfSupplyStateCode: form.placeOfSupply,
    subtotal: totals.subtotal,
    discount: totals.discount,
    taxType,
    taxRate: form.taxRate,
    cgstAmount: totals.cgst,
    sgstAmount: totals.sgst,
    igstAmount: totals.igst,
    total: totals.total,
    amountInWords: amountInWords(totals.total),
    bankAccountId: bank?.id ?? null,
    bankSnapshot: bank ? JSON.stringify(bank) : "",
    signaturePath: form.signaturePath,
    notes: form.notes,
    status: "draft",
    createdAt: "",
    updatedAt: "",
    docType: registered ? "tax_invoice" : "invoice",
    reverseCharge: registered && form.reverseCharge,
    vendorSnapshot: vendorSnapshotJson(settings),
    snapshotOrigin: "issued",
    cancelledAt: null,
    cancelReason: "",
    archivedPdfSha256: null,
    renderPrefs: "",
    items,
  };
}