import { useEffect, useState, useCallback, useMemo } from 'react';
import { Layout, Typography, Switch, Row, Col, Spin, Button, theme, Badge, Empty, Alert } from 'antd';
import { ShoppingCartOutlined, FilterOutlined } from '@ant-design/icons';
import { Link, useLocation, useSearchParams } from 'react-router-dom';
import { Item, FilterOptions, fetchItems, fetchFilterOptions } from './api';
import ItemCard from './components/ItemCard';
import FilterDrawer from './components/FilterDrawer';
import ActiveFilterChips from './components/ActiveFilterChips';
import {
  ItemFilters,
  activeFilterCount,
  filtersFromSearchParams,
  filtersToSearchParams,
  hasActiveFilters
} from './filters';
import AuthPromptModal from './customer/AuthPromptModal';
import { useThemeMode } from './theme/ThemeContext';
import { useCustomerAuth } from './customer/CustomerAuthContext';
import { useCart } from './cart/CartContext';

const { Header, Content, Footer } = Layout;
const { Title } = Typography;

// Dragging the price slider fires a change per pixel; without this every one
// would become its own request.
const FILTER_DEBOUNCE_MS = 250;

export default function App() {
  const [items, setItems] = useState<Item[]>([]);
  const [loading, setLoading] = useState(true);
  const [failed, setFailed] = useState(false);
  const [options, setOptions] = useState<FilterOptions | null>(null);
  const [drawerOpen, setDrawerOpen] = useState(false);
  const [authModalOpen, setAuthModalOpen] = useState(false);
  const [searchParams, setSearchParams] = useSearchParams();
  const location = useLocation();
  const { mode, toggle } = useThemeMode();
  const { customer, loading: authLoading } = useCustomerAuth();
  const { items: cartItems } = useCart();
  const { token } = theme.useToken();

  // The URL is the single source of truth for filter state, so a reload, a
  // shared link, and the back button all restore the same view.
  const filters = useMemo(() => filtersFromSearchParams(searchParams), [searchParams]);
  const filterKey = filtersToSearchParams(filters).toString();

  // "Only my favorites" needs to know who is asking. Until the session has
  // resolved we hold rather than guess: firing the request early would 401 and
  // show the outage banner to someone who is in fact signed in.
  const awaitingAuth = filters.favoritesOnly && authLoading;
  const needsFavoritesAuth = filters.favoritesOnly && !authLoading && !customer;

  const applyFilters = useCallback(
    (next: ItemFilters) => {
      // replace, not push: dragging a slider shouldn't bury the previous page
      // under dozens of history entries.
      setSearchParams(filtersToSearchParams(next), { replace: true });
    },
    [setSearchParams]
  );

  const clearFilters = useCallback(() => {
    setSearchParams(new URLSearchParams(), { replace: true });
  }, [setSearchParams]);

  const load = useCallback(() => {
    return fetchItems(filtersFromSearchParams(new URLSearchParams(filterKey)))
      .then((loaded) => {
        setItems(loaded);
        setFailed(false);
      })
      // A failed request must never fall through to the empty state: telling a
      // customer "no items yet" when the server is broken hides the outage and
      // reads as an empty shop.
      .catch(() => setFailed(true))
      .finally(() => setLoading(false));
  }, [filterKey]);

  useEffect(() => {
    if (awaitingAuth) {
      setLoading(true);
      return;
    }
    // Prompt instead of requesting. The server would answer 401, and rendering
    // that as "no items match these filters" would tell a signed-out visitor
    // they have no favorites rather than that we do not know who they are.
    if (needsFavoritesAuth) {
      setItems([]);
      setFailed(false);
      setLoading(false);
      setAuthModalOpen(true);
      return;
    }
    setLoading(true);
    const timer = setTimeout(() => void load(), FILTER_DEBOUNCE_MS);
    return () => clearTimeout(timer);
  }, [load, awaitingAuth, needsFavoritesAuth]);

  useEffect(() => {
    fetchFilterOptions().then(setOptions).catch(() => setOptions(null));
  }, []);

  // Adding to cart flips an item to reserved, and the filter options' price
  // bounds shift as inventory changes.
  const reload = useCallback(() => {
    void load();
    fetchFilterOptions().then(setOptions).catch(() => undefined);
  }, [load]);

  const activeCount = activeFilterCount(filters);

  return (
    <Layout style={{ minHeight: '100vh' }}>
      <Header
        className="site-header"
        style={{
          background: token.colorBgContainer,
          borderBottom: `1px solid ${token.colorBorderSecondary}`
        }}
      >
        <Title level={3} className="site-header-title" style={{ color: token.colorText }}>
          Redefined Designs
        </Title>
        <div className="site-header-actions">
          <Switch checked={mode === 'dark'} onChange={toggle} checkedChildren="Dark" unCheckedChildren="Light" />
          <Link to="/cart">
            <Badge count={cartItems.length} size="small">
              <Button icon={<ShoppingCartOutlined />} />
            </Badge>
          </Link>
          {/* The account link names the page to render behind the modal, so
              closing it comes back here — filters and all — rather than to a
              default. */}
          {customer ? (
            <Link to="/account" state={{ background: location }}>
              <Button>My Account</Button>
            </Link>
          ) : (
            <>
              <Link to="/login" state={{ background: location }}>
                <Button>Log in</Button>
              </Link>
              <Link to="/register" state={{ background: location }}>
                <Button type="primary">Sign up</Button>
              </Link>
            </>
          )}
        </div>
      </Header>
      <Content style={{ padding: 24 }}>
        <div className="filter-bar">
          <Button
            icon={<FilterOutlined />}
            onClick={() => setDrawerOpen(true)}
            type={activeCount ? 'primary' : 'default'}
          >
            Filters{activeCount ? ` (${activeCount})` : ''}
          </Button>
          <ActiveFilterChips
            options={options}
            filters={filters}
            onChange={applyFilters}
            onClear={clearFilters}
          />
        </div>

        {loading && !items.length && !failed ? <Spin /> : null}
        {failed ? (
          <Alert
            type="error"
            showIcon
            message="Couldn't load items"
            description="The server didn't return the catalogue. This is usually temporary."
            action={<Button size="small" onClick={() => { setLoading(true); void load(); }}>Retry</Button>}
          />
        ) : needsFavoritesAuth ? (
          <Empty description="Sign in to see the items you have favorited">
            <Button type="primary" onClick={() => setAuthModalOpen(true)}>Sign in</Button>
            <Button style={{ marginInlineStart: 8 }} onClick={clearFilters}>Browse everything</Button>
          </Empty>
        ) : !loading && !items.length ? (
          <Empty
            description={
              hasActiveFilters(filters)
                ? 'No items match these filters'
                : 'No items yet — check back soon'
            }
          >
            {hasActiveFilters(filters) ? <Button onClick={clearFilters}>Clear filters</Button> : null}
          </Empty>
        ) : (
          <Row gutter={[20, 20]}>
            {items.map(item => (
              <Col key={item.id} xs={24} sm={12} md={8} lg={6}>
                <ItemCard item={item} onChanged={reload} />
              </Col>
            ))}
          </Row>
        )}
      </Content>
      <Footer style={{ textAlign: 'center', background: token.colorBgContainer }}>
        <Link to="/privacy">Privacy Policy</Link>
      </Footer>

      <FilterDrawer
        open={drawerOpen}
        onClose={() => setDrawerOpen(false)}
        options={options}
        filters={filters}
        onChange={applyFilters}
        onClear={clearFilters}
        resultCount={items.length}
      />

      {/* The same prompt the heart button and Add to Cart use. Signing in
          resolves the gate above, and the filter then applies on its own — the
          customer never has to set it a second time. */}
      <AuthPromptModal
        open={authModalOpen}
        onClose={() => setAuthModalOpen(false)}
        onSuccess={() => setAuthModalOpen(false)}
      />
    </Layout>
  );
}