import { useEffect, useMemo, useState } from "react";
import {
  Button,
  Column,
  Dropdown,
  Grid,
  InlineNotification,
  NumberInput,
  RadioButton,
  RadioButtonGroup,
  Select,
  SelectItem,
  TextArea,
  TextInput,
  Toggle,
} from "@carbon/react";
import { Add, Save, TrashCan } from "@carbon/icons-react";
import { api } from "../lib/api";
import { EMPTY_ITEM, INDIAN_STATES, UNIT_LABELS } from "../lib/types";
import type {
  BankAccount,
  Client,
  InvoiceInput,
  InvoiceItem,
  LineMode,
  LineUnit,
  Settings,
  TaxType,
} from "../lib/types";
import { computeLineAmount, computeTotals } from "../lib/invoice";
import { amountInWords } from "../lib/numberToWords";
import { addDays, formatAmount, todayIso } from "../lib/format";
import { buildPdfProps, exportPdfFromProps } from "../lib/pdf";
import { InvoicePreview } from "../components/InvoicePreview";
import { ImagePicker } from "../components/ImagePicker";
import type { InvoicePdfProps } from "../pdf/InvoiceDocument";

interface NewInvoiceProps {
  settings: Settings;
  onSettingsChange: () => void;
}

export default function NewInvoice({ settings }: NewInvoiceProps) {
  const today = todayIso();
  const [invoiceDate, setInvoiceDate] = useState(today);
  const [dueDate, setDueDate] = useState(addDays(today, settings.paymentTermsDays));
  const [number, setNumber] = useState("");

  const [clients, setClients] = useState<Client[]>([]);
  const [clientId, setClientId] = useState<number | null>(null);
  const [clientName, setClientName] = useState("");
  const [clientAddress, setClientAddress] = useState("");
  const [clientGstin, setClientGstin] = useState("");
  const [poNumber, setPoNumber] = useState("");
  const [placeOfSupply, setPlaceOfSupply] = useState(settings.vendorStateCode);
  const [saveClient, setSaveClient] = useState(false);

  const [items, setItems] = useState<InvoiceItem[]>([{ ...EMPTY_ITEM }]);
  const [discount, setDiscount] = useState(0);

  const [taxesApplicable, setTaxesApplicable] = useState(settings.defaultTaxType !== "none");
  const [taxType, setTaxType] = useState<TaxType>(
    settings.defaultTaxType === "none" ? "cgst_sgst" : settings.defaultTaxType,
  );
  const [taxRate, setTaxRate] = useState(settings.defaultTaxRate);

  const [banks, setBanks] = useState<BankAccount[]>([]);
  const [bankId, setBankId] = useState<number | null>(settings.defaultBankId);
  const [signaturePath, setSignaturePath] = useState<string | null>(settings.signaturePath);
  const [notes, setNotes] = useState("");

  const [logoUri, setLogoUri] = useState<string | null>(null);
  const [signatureUri, setSignatureUri] = useState<string | null>(null);

  const [saving, setSaving] = useState(false);
  const [error, setError] = useState<string | null>(null);
  const [saved, setSaved] = useState<string | null>(null);

  useEffect(() => {
    let active = true;
    (async () => {
      try {
        const [next, clientList, bankList] = await Promise.all([
          api.peekNextInvoiceNumber(),
          api.listClients(),
          api.listBanks(),
        ]);
        if (!active) return;
        setNumber(next);
        setClients(clientList);
        setBanks(bankList);
      } catch (e) {
        if (active) setError(String(e));
      }
    })();
    return () => {
      active = false;
    };
  }, []);

  useEffect(() => {
    let active = true;
    if (!settings.logoPath) {
      setLogoUri(null);
      return;
    }
    api.readAssetDataUri(settings.logoPath).then((uri) => active && setLogoUri(uri)).catch(() => {});
    return () => {
      active = false;
    };
  }, [settings.logoPath]);

  useEffect(() => {
    let active = true;
    if (!signaturePath) {
      setSignatureUri(null);
      return;
    }
    api.readAssetDataUri(signaturePath).then((uri) => active && setSignatureUri(uri)).catch(() => {});
    return () => {
      active = false;
    };
  }, [signaturePath]);

  const effectiveTaxType: TaxType = taxesApplicable ? taxType : "none";
  const totals = useMemo(
    () => computeTotals(items, discount, effectiveTaxType, taxRate),
    [items, discount, effectiveTaxType, taxRate],
  );
  const words = useMemo(() => amountInWords(totals.total), [totals.total]);
  const bank = useMemo(() => banks.find((b) => b.id === bankId) ?? null, [banks, bankId]);

  const previewProps: InvoicePdfProps = {
    vendor: settings,
    bank,
    logoDataUri: logoUri,
    signatureDataUri: signatureUri,
    number: number || "DRAFT",
    invoiceDate,
    dueDate,
    clientName,
    clientAddress,
    clientGstin,
    poNumber,
    placeOfSupplyStateCode: placeOfSupply,
    items,
    subtotal: totals.subtotal,
    discount: totals.discount,
    taxType: effectiveTaxType,
    taxRate,
    cgst: totals.cgst,
    sgst: totals.sgst,
    igst: totals.igst,
    total: totals.total,
    amountInWords: words,
    notes,
  };

  const updateItem = (index: number, patch: Partial<InvoiceItem>) =>
    setItems((prev) => prev.map((item, i) => (i === index ? { ...item, ...patch } : item)));

  const addItem = () => setItems((prev) => [...prev, { ...EMPTY_ITEM }]);
  const removeItem = (index: number) =>
    setItems((prev) => (prev.length === 1 ? prev : prev.filter((_, i) => i !== index)));

  const applyClient = (selected: Client) => {
    setClientId(selected.id);
    setClientName(selected.name);
    setClientAddress(selected.address);
    setClientGstin(selected.gstin);
    setPoNumber(selected.poNumber);
    if (selected.stateCode) setPlaceOfSupply(selected.stateCode);
  };

  const resetForNext = async () => {
    setClientId(null);
    setClientName("");
    setClientAddress("");
    setClientGstin("");
    setPoNumber("");
    setSaveClient(false);
    setItems([{ ...EMPTY_ITEM }]);
    setDiscount(0);
    setNotes("");
    setInvoiceDate(todayIso());
    setDueDate(addDays(todayIso(), settings.paymentTermsDays));
    try {
      setNumber(await api.peekNextInvoiceNumber());
      setClients(await api.listClients());
    } catch {
      /* ignore */
    }
  };

  const onSave = async () => {
    setSaving(true);
    setError(null);
    setSaved(null);
    try {
      const input: InvoiceInput = {
        invoiceDate,
        dueDate,
        clientId,
        clientName,
        clientAddress,
        clientGstin,
        poNumber,
        placeOfSupplyStateCode: placeOfSupply,
        subtotal: totals.subtotal,
        discount: totals.discount,
        taxType: effectiveTaxType,
        taxRate,
        cgstAmount: totals.cgst,
        sgstAmount: totals.sgst,
        igstAmount: totals.igst,
        total: totals.total,
        amountInWords: words,
        bankAccountId: bankId,
        bankSnapshot: bank ? JSON.stringify(bank) : "",
        signaturePath,
        notes,
        saveClient,
        items: items.map((item, index) => ({
          ...item,
          sortOrder: index,
          amount: computeLineAmount(item),
        })),
      };
      const invoice = await api.createInvoice(input);
      const props = await buildPdfProps(invoice, settings, bank);
      const path = await exportPdfFromProps(props, invoice.number);
      if (path) setSaved(path);
      await resetForNext();
    } catch (e) {
      setError(String(e));
    } finally {
      setSaving(false);
    }
  };

  return (
    <div className="voiced-page">
      <Grid>
        <Column sm={4} md={8} lg={16}>
          <div style={{ display: "flex", justifyContent: "space-between", alignItems: "flex-end", gap: "1rem", flexWrap: "wrap" }}>
            <div>
              <h1 className="voiced-page__title">New invoice</h1>
              <p className="voiced-page__subtitle" style={{ marginBottom: 0 }}>
                Next number: <strong>{number || "—"}</strong>
              </p>
            </div>
            <div className="voiced-header-action">
              <Button kind="ghost" onClick={resetForNext} disabled={saving}>
                Clear
              </Button>
              <Button renderIcon={Save} onClick={onSave} disabled={saving}>
                {saving ? "Saving…" : "Save & export PDF"}
              </Button>
            </div>
          </div>
          {error ? (
            <InlineNotification kind="error" lowContrast title="Could not save invoice" subtitle={error} />
          ) : null}
          {saved ? (
            <InlineNotification
              kind="success"
              lowContrast
              title="Invoice saved"
              subtitle={saved}
              onCloseButtonClick={() => setSaved(null)}
            />
          ) : null}
          <div style={{ marginTop: "1.5rem" }} />
        </Column>

        <Column sm={4} md={8} lg={9} className="voiced-stack">
          <Grid narrow>
            <Column sm={4} md={4} lg={5}>
              <TextInput
                id="invoiceDate"
                type="date"
                labelText="Invoice date"
                value={invoiceDate}
                onChange={(e) => {
                  setInvoiceDate(e.target.value);
                  setDueDate(addDays(e.target.value, settings.paymentTermsDays));
                }}
              />
            </Column>
            <Column sm={4} md={4} lg={5}>
              <TextInput
                id="dueDate"
                type="date"
                labelText={`Due date (net ${settings.paymentTermsDays} days)`}
                value={dueDate}
                onChange={(e) => setDueDate(e.target.value)}
              />
            </Column>
            <Column sm={4} md={8} lg={6}>
              <TextInput id="invoiceNumber" labelText="Invoice number" value={number} readOnly />
            </Column>

            <Column sm={4} md={8} lg={8}>
              <Dropdown
                id="savedClient"
                titleText="Saved client (optional)"
                label="Select a saved client to autofill"
                items={clients}
                itemToString={(item) => (item ? item.name : "")}
                onChange={({ selectedItem }) => selectedItem && applyClient(selectedItem)}
              />
            </Column>
            <Column sm={4} md={8} lg={8}>
              <TextInput
                id="clientName"
                labelText="Client name"
                value={clientName}
                onChange={(e) => {
                  setClientName(e.target.value);
                  setClientId(null);
                }}
              />
            </Column>
            <Column sm={4} md={8} lg={16}>
              <TextArea
                id="clientAddress"
                labelText="Client address"
                rows={3}
                value={clientAddress}
                onChange={(e) => setClientAddress(e.target.value)}
              />
            </Column>
            <Column sm={4} md={4} lg={5}>
              <TextInput
                id="clientGstin"
                labelText="Client GSTIN (optional)"
                value={clientGstin}
                onChange={(e) => setClientGstin(e.target.value.toUpperCase())}
              />
            </Column>
            <Column sm={4} md={4} lg={5}>
              <TextInput
                id="poNumber"
                labelText="PO number (optional)"
                value={poNumber}
                onChange={(e) => setPoNumber(e.target.value)}
              />
            </Column>
            <Column sm={4} md={8} lg={6}>
              <Select
                id="placeOfSupply"
                labelText="Place of supply"
                value={placeOfSupply}
                onChange={(e) => setPlaceOfSupply(e.target.value)}
              >
                {INDIAN_STATES.map((s) => (
                  <SelectItem key={s.code} value={s.code} text={`${s.code} — ${s.name}`} />
                ))}
              </Select>
            </Column>
            <Column sm={4} md={8} lg={16}>
              <Toggle
                id="saveClient"
                labelText="Save this client for next time"
                toggled={saveClient}
                onToggle={setSaveClient}
              />
            </Column>
          </Grid>

          <div>
            <h3 style={{ marginBottom: "0.75rem" }}>Line items</h3>
            {items.map((item, index) => (
              <div
                key={index}
                style={{
                  display: "flex",
                  flexWrap: "wrap",
                  gap: "0.5rem",
                  alignItems: "flex-end",
                  padding: "0.75rem",
                  border: "1px solid var(--cds-border-subtle-01)",
                  marginBottom: "0.5rem",
                }}
              >
                <div style={{ flex: "3 1 240px" }}>
                  <TextInput
                    id={`desc-${index}`}
                    labelText="Particulars / description"
                    value={item.description}
                    onChange={(e) => updateItem(index, { description: e.target.value })}
                  />
                </div>
                <div style={{ flex: "0 1 150px" }}>
                  <Select
                    id={`mode-${index}`}
                    labelText="Type"
                    value={item.mode}
                    onChange={(e) => updateItem(index, { mode: e.target.value as LineMode })}
                  >
                    <SelectItem value="fixed" text="Fixed amount" />
                    <SelectItem value="rate" text="Rate × quantity" />
                  </Select>
                </div>
                {item.mode === "rate" ? (
                  <>
                    <div style={{ flex: "0 1 130px" }}>
                      <NumberInput
                        id={`rate-${index}`}
                        label="Rate (₹)"
                        min={0}
                        step={1}
                        value={item.rate}
                        onChange={(_e, { value }) => updateItem(index, { rate: Number(value) || 0 })}
                      />
                    </div>
                    <div style={{ flex: "0 1 140px" }}>
                      <Select
                        id={`unit-${index}`}
                        labelText="Unit"
                        value={item.unit}
                        onChange={(e) => updateItem(index, { unit: e.target.value as LineUnit })}
                      >
                        {Object.entries(UNIT_LABELS).map(([value, text]) => (
                          <SelectItem key={value} value={value} text={text} />
                        ))}
                      </Select>
                    </div>
                    <div style={{ flex: "0 1 110px" }}>
                      <NumberInput
                        id={`qty-${index}`}
                        label="Quantity"
                        min={0}
                        step={1}
                        value={item.quantity}
                        onChange={(_e, { value }) => updateItem(index, { quantity: Number(value) || 0 })}
                      />
                    </div>
                  </>
                ) : (
                  <div style={{ flex: "0 1 150px" }}>
                    <NumberInput
                      id={`amount-${index}`}
                      label="Amount (₹)"
                      min={0}
                      step={1}
                      value={item.amount}
                      onChange={(_e, { value }) => updateItem(index, { amount: Number(value) || 0 })}
                    />
                  </div>
                )}
                <div style={{ flex: "0 0 auto", paddingBottom: "0.4rem" }}>
                  <strong>₹{formatAmount(computeLineAmount(item))}</strong>
                </div>
                <Button
                  kind="ghost"
                  size="sm"
                  hasIconOnly
                  renderIcon={TrashCan}
                  iconDescription="Remove line"
                  onClick={() => removeItem(index)}
                  disabled={items.length === 1}
                />
              </div>
            ))}
            <Button kind="tertiary" size="sm" renderIcon={Add} onClick={addItem}>
              Add line
            </Button>
          </div>

          <Grid narrow>
            <Column sm={4} md={4} lg={8}>
              <NumberInput
                id="discount"
                label="Discount (₹)"
                min={0}
                step={1}
                value={discount}
                onChange={(_e, { value }) => setDiscount(Number(value) || 0)}
              />
            </Column>
            <Column sm={4} md={8} lg={16}>
              <Toggle
                id="taxes"
                labelText="Taxes applicable"
                toggled={taxesApplicable}
                onToggle={setTaxesApplicable}
              />
            </Column>
            {taxesApplicable ? (
              <>
                <Column sm={4} md={8} lg={16}>
                  <RadioButtonGroup
                    legendText="Tax treatment"
                    name="taxType"
                    valueSelected={taxType}
                    onChange={(value) => setTaxType(value as TaxType)}
                  >
                    <RadioButton id="t-cgst" labelText="CGST + SGST (within state)" value="cgst_sgst" />
                    <RadioButton id="t-igst" labelText="IGST (inter-state)" value="igst" />
                  </RadioButtonGroup>
                </Column>
                <Column sm={4} md={4} lg={8}>
                  <NumberInput
                    id="taxRate"
                    label="Tax rate (%)"
                    min={0}
                    max={100}
                    step={0.5}
                    value={taxRate}
                    onChange={(_e, { value }) => setTaxRate(Number(value) || 0)}
                  />
                </Column>
              </>
            ) : null}
          </Grid>

          <Select
            id="bankAccount"
            labelText="Bank account (Pay To)"
            value={bankId ?? ""}
            onChange={(e) => setBankId(e.target.value ? Number(e.target.value) : null)}
          >
            <SelectItem value="" text="No bank details" />
            {banks.map((b) => (
              <SelectItem
                key={b.id ?? 0}
                value={String(b.id)}
                text={`${b.bankName} · ${b.accountNo}`}
              />
            ))}
          </Select>

          <ImagePicker
            kind="signature"
            label="Signature for this invoice (optional)"
            value={signaturePath}
            onChange={setSignaturePath}
          />

          <TextArea
            id="notes"
            labelText="Notes (optional)"
            rows={2}
            value={notes}
            onChange={(e) => setNotes(e.target.value)}
          />
        </Column>

        <Column sm={4} md={8} lg={7}>
          <div style={{ position: "sticky", top: "3rem" }}>
            <h3 style={{ marginBottom: "0.75rem" }}>Preview</h3>
            <InvoicePreview {...previewProps} />
          </div>
        </Column>
      </Grid>
    </div>
  );
}