import type { ShopSettings } from "@prisma/client";

import type { RawOrderForInvoice, RawShippingLine, RawTaxLine } from "./loadOrderForInvoice.server";
import type {
  InvoiceLine,
  InvoiceNotice,
  InvoiceTotals,
  InvoiceViewModel,
  IssuerData,
  RecipientData,
  TrackingInfo,
  VatBreakdownEntry,
} from "./types";
import { addDays } from "./format";
import { derivePaymentStatus, getStrings, pickLanguage, type InvoiceLanguage } from "./i18n";

interface ComposeArgs {
  order: RawOrderForInvoice;
  settings: ShopSettings;
  invoiceNumber: string;
  /** Language override (e.g. for Storno copies). */
  forceLanguage?: InvoiceLanguage;
  /**
   * When set, produces a Stornorechnung view model: line and total amounts
   * are negated, `kind` is `"storno"`, and `cancelsNumber` references the
   * original invoice number. Notices, GiroCode and payment-due date are
   * suppressed (a storno is informational, not a request for payment).
   */
  storno?: { cancelsNumber: string };
  /** Optional override for invoice/delivery date (defaults to order date). */
  issueDate?: Date;
  /**
   * When true, render as an Angebot/Offer instead of an invoice:
   * - `kind = "offer"`
   * - no payment-due date (the dueDate field is repurposed by the renderer
   *   as the offer's validity expiry).
   * - GiroCode and payment-terms text are suppressed.
   */
  offer?: boolean;
}

export function composeInvoice({
  order,
  settings,
  invoiceNumber,
  forceLanguage,
  storno,
  issueDate,
  offer,
}: ComposeArgs): InvoiceViewModel {
  const language = forceLanguage
    ?? pickLanguage(order.customer?.locale ?? settings.defaultLanguage);

  const issuer = mapIssuer(settings);
  const recipient = mapRecipient(order);
  const isB2B = !!order.purchasingEntity?.company;
  const recipientVatId = order.purchasingEntity?.company?.vatId ?? undefined;

  const strings = getStrings(language);
  let { lines, totals } = mapLinesAndTotals(order, {
    shippingItemPrefix: strings.shippingItemPrefix,
  });
  let notices = deriveNotices({ order, settings, isB2B });

  const separateShippingAddress = mapSeparateShippingAddress(order);
  const shippingMethod = order.shippingLine?.title?.trim() || undefined;
  const tracking = mapTracking(order);

  const invoiceDate = issueDate ?? new Date(order.processedAt ?? order.createdAt);
  const deliveryDate = invoiceDate;
  // For offers we treat `dueDate` as the offer's validity expiry (default 30
  // days from issue). The PDF renderer renders a different label.
  const dueDate = offer
    ? addDays(invoiceDate, 30)
    : !storno && settings.paymentTermDays > 0
      ? addDays(invoiceDate, settings.paymentTermDays)
      : undefined;

  const paid = (order.displayFinancialStatus || "").toUpperCase() === "PAID";
  const paymentStatus = derivePaymentStatus(order.displayFinancialStatus);
  const paymentGatewayNames = (order.paymentGatewayNames ?? []).filter(
    (n) => typeof n === "string" && n.trim().length > 0,
  );

  if (storno) {
    lines = lines.map((l) => ({
      ...l,
      unitPriceNet: -l.unitPriceNet,
      totalNet: -l.totalNet,
    }));
    totals = {
      net: -totals.net,
      vatBreakdown: totals.vatBreakdown.map((v) => ({
        ratePct: v.ratePct,
        net: -v.net,
        tax: -v.tax,
      })),
      totalVat: -totals.totalVat,
      gross: -totals.gross,
    };
    // Notices are still relevant (e.g. reverse-charge), but the storno is not
    // a payment request — leave them in place for legal symmetry.
  }

  return {
    language,
    currency: order.currencyCode,
    kind: storno ? "storno" : offer ? "offer" : "invoice",
    number: invoiceNumber,
    cancelsNumber: storno?.cancelsNumber,
    invoiceDate,
    deliveryDate,
    dueDate,
    issuer,
    recipient,
    isB2B,
    recipientVatId,
    lines,
    totals,
    notices,
    paid,
    paymentStatus,
    paymentGatewayNames,
    orderName: order.name,
    separateShippingAddress,
    shippingMethod,
    tracking,
  };
}

function mapIssuer(s: ShopSettings): IssuerData {
  return {
    companyName: s.companyName,
    legalForm: s.legalForm,
    ownerName: s.ownerName,
    addressLine1: s.addressLine1,
    addressLine2: s.addressLine2,
    postalCode: s.postalCode,
    city: s.city,
    countryCode: s.countryCode,
    phone: s.phone,
    email: s.email,
    website: s.website,
    vatId: s.vatId,
    taxNumber: s.taxNumber,
    registrationNo: s.registrationNo,
    registrationCourt: s.registrationCourt,
    bankName: s.bankName,
    iban: s.iban,
    bic: s.bic,
    footerNote: s.footerNote,
    footerNoteEn: s.footerNoteEn,
  };
}

function mapRecipient(order: RawOrderForInvoice): RecipientData {
  // Prefer billingAddress; fall back to shippingAddress; fall back to customer name only.
  const a = order.billingAddress ?? order.shippingAddress ?? null;
  const customerFullName = [order.customer?.firstName, order.customer?.lastName]
    .filter(Boolean)
    .join(" ")
    .trim();

  if (!a) {
    return {
      name: customerFullName,
      company: order.purchasingEntity?.company?.name ?? "",
      addressLine1: "",
      addressLine2: "",
      postalCode: "",
      city: "",
      countryCode: "",
    };
  }

  return {
    name: a.name ?? customerFullName,
    company: a.company ?? order.purchasingEntity?.company?.name ?? "",
    addressLine1: a.address1 ?? "",
    addressLine2: a.address2 ?? "",
    postalCode: a.zip ?? "",
    city: a.city ?? "",
    countryCode: a.countryCode ?? "",
  };
}

function mapLinesAndTotals(
  order: RawOrderForInvoice,
  opts: { shippingItemPrefix: string },
): {
  lines: InvoiceLine[];
  totals: InvoiceTotals;
} {
  const taxesIncluded = order.taxesIncluded;
  const linesOut: InvoiceLine[] = [];
  const vatMap = new Map<number, VatBreakdownEntry>();
  let netSum = 0;

  order.lineItems.forEach((li, idx) => {
    const qty = li.quantity;
    const grossOrNetUnit = parseFloat(li.originalUnitPriceSet.shopMoney.amount);
    // Total tax for this line summed across its tax lines.
    const lineTax = li.taxLines.reduce(
      (acc, t) => acc + parseFloat(t.priceSet.shopMoney.amount),
      0,
    );
    // If taxes are included in the unit price, subtract them to get net.
    const lineGross = grossOrNetUnit * qty + (taxesIncluded ? 0 : lineTax);
    const lineNet = taxesIncluded ? grossOrNetUnit * qty - lineTax : grossOrNetUnit * qty;
    const unitNet = qty > 0 ? lineNet / qty : 0;

    linesOut.push({
      position: idx + 1,
      title: li.title,
      sku: li.sku ?? undefined,
      quantity: qty,
      unitPriceNet: round2(unitNet),
      totalNet: round2(lineNet),
      imageUrl: li.imageUrl ?? undefined,
    });

    netSum += lineNet;

    li.taxLines.forEach((t) => accumulateVat(vatMap, t, parseFloat(t.priceSet.shopMoney.amount), lineNet));
    void lineGross;
  });

  // Prefer order-level taxLines for the breakdown grouping if line-level is missing.
  if (vatMap.size === 0 && order.taxLines.length > 0) {
    order.taxLines.forEach((t) => {
      const tax = parseFloat(t.priceSet.shopMoney.amount);
      // We don't have per-rate net from the order level; approximate by inferring from rate.
      const rate = normaliseRate(t);
      const net = rate > 0 ? tax / (rate / 100) : 0;
      const entry = vatMap.get(rate) || { ratePct: rate, net: 0, tax: 0 };
      entry.net += net;
      entry.tax += tax;
      vatMap.set(rate, entry);
    });
  }

  // Append the shipping line as a synthetic invoice row when the order has
  // a shipping cost > 0. This makes shipping appear in the items table
  // (visible to the customer) and folds its tax into the VAT breakdown.
  const shippingLineNet = appendShippingLine(
    order.shippingLine,
    taxesIncluded,
    linesOut,
    vatMap,
    opts.shippingItemPrefix,
  );
  netSum += shippingLineNet;

  const vatBreakdown = Array.from(vatMap.values())
    .map((e) => ({ ratePct: e.ratePct, net: round2(e.net), tax: round2(e.tax) }))
    .filter((e) => e.tax > 0)
    .sort((a, b) => a.ratePct - b.ratePct);

  const totalVat = vatBreakdown.reduce((acc, e) => acc + e.tax, 0);
  const grossFromOrder = order.totalPriceSet
    ? parseFloat(order.totalPriceSet.shopMoney.amount)
    : netSum + totalVat;

  return {
    lines: linesOut,
    totals: {
      net: round2(netSum),
      vatBreakdown,
      totalVat: round2(totalVat),
      gross: round2(grossFromOrder),
    },
  };
}

function accumulateVat(
  vatMap: Map<number, VatBreakdownEntry>,
  t: RawTaxLine,
  taxAmount: number,
  lineNet: number,
) {
  if (taxAmount <= 0) return;
  const rate = normaliseRate(t);
  const entry = vatMap.get(rate) || { ratePct: rate, net: 0, tax: 0 };
  entry.net += lineNet;
  entry.tax += taxAmount;
  vatMap.set(rate, entry);
}

function normaliseRate(t: RawTaxLine): number {
  if (t.ratePercentage != null) return Number(t.ratePercentage);
  if (t.rate != null) {
    const r = Number(t.rate);
    return r <= 1 ? r * 100 : r;
  }
  return 0;
}

function round2(n: number): number {
  return Math.round(n * 100) / 100;
}

function deriveNotices({
  order,
  settings,
  isB2B,
}: {
  order: RawOrderForInvoice;
  settings: ShopSettings;
  isB2B: boolean;
}): InvoiceNotice[] {
  const notices: InvoiceNotice[] = [];
  const totalTax = order.totalTaxSet
    ? parseFloat(order.totalTaxSet.shopMoney.amount)
    : 0;
  const recipientCountry =
    order.billingAddress?.countryCode || order.shippingAddress?.countryCode || "";
  const issuerCountry = settings.countryCode || "AT";

  if (settings.kleinunternehmer) {
    notices.push({ kind: "kleinunternehmer" });
    return notices; // exclusive of the others
  }

  if (totalTax === 0) {
    if (
      isB2B &&
      recipientCountry &&
      recipientCountry !== issuerCountry &&
      isEuCountry(recipientCountry)
    ) {
      notices.push({ kind: "reverseCharge" });
    } else if (recipientCountry && !isEuCountry(recipientCountry)) {
      notices.push({ kind: "export" });
    }
  }

  return notices;
}

const EU_COUNTRIES = new Set([
  "AT","BE","BG","CY","CZ","DE","DK","EE","ES","FI","FR","GR","HR","HU","IE",
  "IT","LT","LU","LV","MT","NL","PL","PT","RO","SE","SI","SK",
]);

function isEuCountry(code: string): boolean {
  return EU_COUNTRIES.has(code.toUpperCase());
}

/**
 * Add a synthetic line item for the order's shipping cost. Returns the net
 * amount added (used to keep the running net subtotal in sync). Returns 0
 * when there's no shipping line or the shipping price is zero (e.g. free
 * shipping or digital orders).
 */
function appendShippingLine(
  shippingLine: RawShippingLine | null,
  taxesIncluded: boolean,
  linesOut: InvoiceLine[],
  vatMap: Map<number, VatBreakdownEntry>,
  prefix: string,
): number {
  if (!shippingLine) return 0;
  const priceSet = shippingLine.discountedPriceSet ?? shippingLine.originalPriceSet;
  const grossOrNet = priceSet ? parseFloat(priceSet.shopMoney.amount) : 0;
  if (!Number.isFinite(grossOrNet) || grossOrNet === 0) return 0;

  const tax = shippingLine.taxLines.reduce(
    (acc, t) => acc + parseFloat(t.priceSet.shopMoney.amount),
    0,
  );
  const net = taxesIncluded ? grossOrNet - tax : grossOrNet;

  const title = shippingLine.title?.trim()
    ? `${prefix}: ${shippingLine.title.trim()}`
    : prefix;

  linesOut.push({
    position: linesOut.length + 1,
    title,
    quantity: 1,
    unitPriceNet: round2(net),
    totalNet: round2(net),
  });

  shippingLine.taxLines.forEach((t) =>
    accumulateVat(vatMap, t, parseFloat(t.priceSet.shopMoney.amount), net),
  );

  return net;
}

/**
 * Returns the shipping address as a recipient block when it differs in any
 * meaningful way from the billing address. Returns undefined when both are
 * the same (so the renderer doesn't show a redundant block) or when there
 * is no shipping address at all.
 */
function mapSeparateShippingAddress(
  order: RawOrderForInvoice,
): RecipientData | undefined {
  const ship = order.shippingAddress;
  const bill = order.billingAddress;
  if (!ship) return undefined;
  // No billing address → just use the existing recipient block, no need to
  // duplicate.
  if (!bill) return undefined;

  const sameAddress =
    (ship.name ?? "") === (bill.name ?? "") &&
    (ship.company ?? "") === (bill.company ?? "") &&
    (ship.address1 ?? "") === (bill.address1 ?? "") &&
    (ship.address2 ?? "") === (bill.address2 ?? "") &&
    (ship.zip ?? "") === (bill.zip ?? "") &&
    (ship.city ?? "") === (bill.city ?? "") &&
    (ship.countryCode ?? "") === (bill.countryCode ?? "");
  if (sameAddress) return undefined;

  const customerFullName = [order.customer?.firstName, order.customer?.lastName]
    .filter(Boolean)
    .join(" ")
    .trim();

  return {
    name: ship.name ?? customerFullName,
    company: ship.company ?? "",
    addressLine1: ship.address1 ?? "",
    addressLine2: ship.address2 ?? "",
    postalCode: ship.zip ?? "",
    city: ship.city ?? "",
    countryCode: ship.countryCode ?? "",
  };
}

/**
 * Flatten tracking info from all fulfillments. Skips entries without a
 * tracking number. Deduplicates on `number`.
 */
function mapTracking(order: RawOrderForInvoice): TrackingInfo[] {
  const out: TrackingInfo[] = [];
  const seen = new Set<string>();
  for (const f of order.fulfillments ?? []) {
    for (const t of f.trackingInfo ?? []) {
      const number = (t.number ?? "").trim();
      if (!number || seen.has(number)) continue;
      seen.add(number);
      out.push({
        number,
        url: t.url?.trim() || undefined,
        company: t.company?.trim() || undefined,
      });
    }
  }
  return out;
}