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 pickupInfo = detectPickup(order);
  const isPickup = pickupInfo != null;
  const separateShippingAddress = isPickup ? undefined : mapSeparateShippingAddress(order);
  // For shipping orders we surface the carrier label (e.g. "Standardversand").
  // For pickup orders the meta row uses a different label entirely
  // ("Abholort: <location>") — see the renderer.
  const shippingMethod = isPickup
    ? undefined
    : order.shippingLine?.title?.trim() || undefined;
  const tracking = mapTracking(order);

  const invoiceDate = issueDate ?? new Date(order.processedAt ?? order.createdAt);
  // §11 UStG: deliveryDate is the date goods/services were rendered. Prefer
  // the latest fulfillment timestamp; fall back to invoice date when the
  // order is unfulfilled (e.g. immediate-render services or digital orders).
  const deliveryDate = pickDeliveryDate(order, 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";
  // Refunded gross amount, mirrored from Shopify's `totalRefundedSet`.
  // Storno/offer documents don't carry a refund row — a storno *is*
  // already the cancellation document, and offers have no payments yet.
  const refundedAmount = storno || offer
    ? 0
    : Math.max(0, parseFloat(order.totalRefundedSet?.shopMoney.amount ?? "0") || 0);
  let paymentStatus = derivePaymentStatus(order.displayFinancialStatus);
  // Reclassification: Shopify flips `displayFinancialStatus` to
  // PARTIALLY_REFUNDED as soon as *any* refund is posted against a
  // paid order, even when the customer only got back a small fraction.
  // For our purposes such an order is still "paid" — the merchant kept
  // the difference — and showing "Erstattet" / "Refunded" in the
  // status row would falsely imply the customer got everything back.
  // Only when the refund equals (or, defensively, exceeds) the gross
  // do we keep the "refunded" status.
  if (
    paymentStatus === "refunded" &&
    refundedAmount > 0 &&
    refundedAmount < totals.gross
  ) {
    paymentStatus = "paid";
  }
  // A document only requires payment when it's a regular invoice (not a
  // storno or an offer) AND money is still actually owed. Refunded and
  // paid orders both have a 0 outstanding balance — the difference is
  // just whether the money was kept (`paid`) or returned (`refunded`).
  const requiresPayment =
    !storno && !offer && paymentStatus !== "paid" && paymentStatus !== "refunded";
  const paymentGatewayNames = (order.paymentGatewayNames ?? []).filter(
    (n) => typeof n === "string" && n.trim().length > 0,
  );

  if (storno) {
    lines = lines.map((l) => ({
      ...l,
      unitPriceNet: -l.unitPriceNet,
      originalUnitPriceNet:
        l.originalUnitPriceNet != null ? -l.originalUnitPriceNet : undefined,
      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,
    requiresPayment,
    refundedAmount,
    paymentGatewayNames,
    orderName: order.name,
    separateShippingAddress,
    shippingMethod,
    tracking,
    discountCodes: order.discountCodes ?? [],
    isPickup,
    pickupLocationName: pickupInfo?.locationName ?? undefined,
  };
}

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;
    // Prefer the post-discount unit price when Shopify provides one (it
    // reflects both line-level and cart-level discount allocations). Fall
    // back to original price when no discount applied.
    const grossOrNetUnit = parseFloat(
      (li.discountedUnitPriceSet ?? li.originalUnitPriceSet).shopMoney.amount,
    );
    const originalGrossOrNetUnit = 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;
    // For the strikethrough original, compute net the same way the line is
    // computed: when taxesIncluded, derive an equivalent net per unit using
    // the line's effective tax rate; when not, the original IS the net.
    const effectiveRate = qty > 0 && grossOrNetUnit > 0
      ? lineTax / (grossOrNetUnit * qty)
      : 0;
    const originalUnitNet = taxesIncluded
      ? originalGrossOrNetUnit / (1 + effectiveRate)
      : originalGrossOrNetUnit;
    const hasDiscount =
      Math.round(originalGrossOrNetUnit * 100) !== Math.round(grossOrNetUnit * 100);

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

/**
 * Detects whether the order is a "local pickup" order using three signals
 * (any one is enough). All rely only on the `read_orders` scope.
 *
 *  1. **No shipping address** despite `requiresShipping == true`. Shopify
 *     never lets a regular ship-to-customer order check out without one,
 *     so this combination is a textbook pickup. This is the *only* signal
 *     for the built-in "Shop location" rate, which leaves
 *     `deliveryCategory` null and the title/code as the bare location
 *     name (e.g. "Shop location" / "Lager Graz").
 *  2. `shippingLine.deliveryCategory` contains "pickup"/"local_pickup".
 *     Set by some Local Pickup integrations.
 *  3. Regex on `shippingLine.{source,code,title,carrierIdentifier}` for
 *     custom rates titled "Abholung"/"Pickup".
 *
 * (We deliberately do NOT query `Order.fulfillmentOrders.deliveryMethod`:
 * that field requires the `read_merchant_managed_fulfillment_orders` scope,
 * which would force every install to re-grant permissions.)
 *
 * Location name is taken from `shippingLine.title` — for the Shopify
 * Local Pickup app and the built-in "Shop location" rate, the title IS
 * the chosen location name.
 *
 * Returns the pickup descriptor or `null` when the order is a normal
 * shipping order. Callers should not render the pickup-location address
 * as a separate "delivery address".
 */
function detectPickup(
  order: RawOrderForInvoice,
): { locationName: string | null } | null {
  const sl = order.shippingLine;
  // Strongest signal: shipping is required but there's no shipping address.
  // Shopify rejects checkout otherwise, so this is conclusive.
  const noShipAddrButRequired =
    order.requiresShipping && order.shippingAddress == null;
  // Secondary: explicit pickup category from Local Pickup apps.
  const dc = (sl?.deliveryCategory ?? "").toLowerCase();
  const isPickupCategory = dc.includes("pickup") || dc.includes("pick_up") || dc.includes("pick-up");
  // Tertiary: regex on title/code/source/carrier — covers merchants who
  // model pickup as a custom shipping rate.
  const haystack = [sl?.source, sl?.code, sl?.title, sl?.carrierIdentifier]
    .filter(Boolean)
    .join(" ")
    .toLowerCase();
  const isPickupString = /pick[\s-]?up|abholung|abhol\b/.test(haystack);
  if (!noShipAddrButRequired && !isPickupCategory && !isPickupString) return null;
  return { locationName: sl?.title?.trim() || null };
}

/**
 * Picks the delivery date for §11 UStG: the latest fulfillment timestamp
 * when the order is fulfilled, otherwise the invoice date itself (best
 * approximation for unfulfilled / digital orders).
 */
function pickDeliveryDate(order: RawOrderForInvoice, invoiceDate: Date): Date {
  const stamps = (order.fulfillments ?? [])
    .map((f) => (f.createdAt ? new Date(f.createdAt).getTime() : NaN))
    .filter((n) => Number.isFinite(n));
  if (stamps.length === 0) return invoiceDate;
  return new Date(Math.max(...stamps));
}