import { useState } from 'react';
import { useQuery, useMutation } from '@tanstack/react-query';
import {
  Box,
  Typography,
  Card,
  CardContent,
  Table,
  TableBody,
  TableCell,
  TableContainer,
  TableHead,
  TableRow,
  TablePagination,
  TextField,
  InputAdornment,
  Button,
  Skeleton,
  IconButton,
  Tooltip,
  Dialog,
  DialogTitle,
  DialogContent,
  DialogActions,
  Alert,
} from '@mui/material';
import SearchIcon from '@mui/icons-material/Search';
import AddIcon from '@mui/icons-material/Add';
import EditIcon from '@mui/icons-material/Edit';
import ErrorOutlineIcon from '@mui/icons-material/ErrorOutlined';
import { toast } from 'react-toastify';
import {
  customersApi,
  type Customer,
  type PagedCustomerResponse,
  type CreateCustomerRequest,
  type UpdateCustomerRequest,
} from '../../../lib/api/customers';
import { queryClient } from '../../../lib/queryClient';
import { QUERY_KEYS } from '../../../constants/queryKeys';
import { DEFAULT_PAGE, DEFAULT_PAGE_SIZE, DEBOUNCE_SEARCH } from '../../../constants';
import { useDocumentTitle } from '../../../hooks/useDocumentTitle';

const COL_COUNT = 4; // Name, Address, Contact Email, Actions

/** Simple email format check (client-side only). */
function isValidEmail(email: string): boolean {
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);
}

interface CustomerFormState {
  name: string;
  address: string;
  contactEmail: string;
}

const EMPTY_FORM: CustomerFormState = { name: '', address: '', contactEmail: '' };

export default function CustomerManagementPage() {
  useDocumentTitle('Customer Management');

  // --- List state ---
  const [search, setSearch] = useState('');
  const [debouncedSearch, setDebouncedSearch] = useState('');
  const [page, setPage] = useState(DEFAULT_PAGE);
  const [pageSize, setPageSize] = useState(DEFAULT_PAGE_SIZE);

  // Debounce search input
  const [debounceTimer, setDebounceTimer] = useState<ReturnType<typeof setTimeout> | null>(null);

  const handleSearchChange = (value: string) => {
    setSearch(value);
    if (debounceTimer) clearTimeout(debounceTimer);
    const timer = setTimeout(() => {
      setDebouncedSearch(value);
      setPage(1);
    }, DEBOUNCE_SEARCH);
    setDebounceTimer(timer);
  };

  const {
    data,
    isLoading,
    isError,
    refetch,
  } = useQuery<PagedCustomerResponse>({
    queryKey: [QUERY_KEYS.customerList, debouncedSearch, page, pageSize],
    queryFn: () => customersApi.list({ search: debouncedSearch || undefined, page, pageSize }),
  });

  const rows = data?.items ?? [];
  const totalCount = data?.totalCount ?? 0;

  // --- Dialog state ---
  const [dialogOpen, setDialogOpen] = useState(false);
  const [editingCustomer, setEditingCustomer] = useState<Customer | null>(null);
  const [form, setForm] = useState<CustomerFormState>(EMPTY_FORM);
  const [formErrors, setFormErrors] = useState<Partial<Record<keyof CustomerFormState, string>>>({});

  const isEditing = editingCustomer !== null;

  const openCreateDialog = () => {
    setEditingCustomer(null);
    setForm(EMPTY_FORM);
    setFormErrors({});
    setDialogOpen(true);
  };

  const openEditDialog = (customer: Customer) => {
    setEditingCustomer(customer);
    setForm({
      name: customer.name,
      address: customer.addresses?.[0] ?? '',
      contactEmail: customer.contactEmail ?? '',
    });
    setFormErrors({});
    setDialogOpen(true);
  };

  const closeDialog = () => {
    setDialogOpen(false);
    setEditingCustomer(null);
    setForm(EMPTY_FORM);
    setFormErrors({});
  };

  const validateForm = (): boolean => {
    const errors: Partial<Record<keyof CustomerFormState, string>> = {};
    if (!form.name.trim()) errors.name = 'Name is required';
    if (!form.address.trim()) errors.address = 'Address is required';
    if (form.contactEmail.trim() && !isValidEmail(form.contactEmail.trim())) {
      errors.contactEmail = 'Enter a valid email address';
    }
    setFormErrors(errors);
    return Object.keys(errors).length === 0;
  };

  const handleFieldChange = (field: keyof CustomerFormState, value: string) => {
    setForm((prev) => ({ ...prev, [field]: value }));
    // Clear field error on change
    if (formErrors[field]) {
      setFormErrors((prev) => {
        const next = { ...prev };
        delete next[field];
        return next;
      });
    }
  };

  // --- Mutations ---
  const createMutation = useMutation({
    mutationFn: (data: CreateCustomerRequest) => customersApi.create(data),
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: [QUERY_KEYS.customerList] });
      closeDialog();
      toast.success('Customer created');
    },
    onError: (error: Error) => {
      toast.error(`Failed to create customer: ${error.message}`);
    },
  });

  const updateMutation = useMutation({
    mutationFn: ({ id, data }: { id: string; data: UpdateCustomerRequest }) =>
      customersApi.update(id, data),
    onSuccess: () => {
      queryClient.invalidateQueries({ queryKey: [QUERY_KEYS.customerList] });
      closeDialog();
      toast.success('Customer updated');
    },
    onError: (error: Error) => {
      toast.error(`Failed to update customer: ${error.message}`);
    },
  });

  const handleSubmit = () => {
    if (!validateForm()) return;

    const payload = {
      name: form.name.trim(),
      address: form.address.trim(),
      ...(form.contactEmail.trim() ? { contactEmail: form.contactEmail.trim() } : {}),
    };

    if (isEditing) {
      updateMutation.mutate({ id: editingCustomer.id, data: payload });
    } else {
      createMutation.mutate(payload);
    }
  };

  const isSaving = createMutation.isPending || updateMutation.isPending;

  return (
    <Box>
      <Box sx={{ display: 'flex', alignItems: 'center', justifyContent: 'space-between', mb: 3 }}>
        <Typography variant="h5">Customer Management</Typography>
        <Button
          variant="contained"
          startIcon={<AddIcon />}
          onClick={openCreateDialog}
        >
          New Customer
        </Button>
      </Box>

      <Card>
        <CardContent sx={{ pb: 0 }}>
          {/* Search bar */}
          <Box sx={{ display: 'flex', gap: 2, mb: 2, flexWrap: 'wrap' }}>
            <TextField
              size="small"
              placeholder="Search customers..."
              value={search}
              onChange={(e) => handleSearchChange(e.target.value)}
              sx={{ width: 300 }}
              slotProps={{
                input: {
                  startAdornment: (
                    <InputAdornment position="start">
                      <SearchIcon fontSize="small" />
                    </InputAdornment>
                  ),
                },
              }}
            />
          </Box>

          {/* Error state */}
          {isError && (
            <Alert
              severity="error"
              icon={<ErrorOutlineIcon />}
              action={
                <Button color="inherit" size="small" onClick={() => refetch()}>
                  Retry
                </Button>
              }
              sx={{ mb: 2 }}
            >
              Failed to load customers. Please try again.
            </Alert>
          )}

          {/* Table */}
          <TableContainer>
            <Table size="small">
              <TableHead>
                <TableRow>
                  <TableCell>Name</TableCell>
                  <TableCell>Address</TableCell>
                  <TableCell>Contact Email</TableCell>
                  <TableCell sx={{ width: 60 }} />
                </TableRow>
              </TableHead>
              <TableBody>
                {isLoading
                  ? Array.from({ length: 5 }).map((_, i) => (
                      <TableRow key={i}>
                        {Array.from({ length: COL_COUNT }).map((_, j) => (
                          <TableCell key={j}>
                            <Skeleton variant="text" />
                          </TableCell>
                        ))}
                      </TableRow>
                    ))
                  : rows.map((customer) => (
                      <TableRow key={customer.id} hover>
                        <TableCell sx={{ fontWeight: 600 }}>{customer.name}</TableCell>
                        <TableCell>{customer.addresses?.[0] ?? '-'}</TableCell>
                        <TableCell>
                          {customer.contactEmail ? (
                            customer.contactEmail
                          ) : (
                            <Typography
                              component="span"
                              sx={{ color: '#94A3B8', fontStyle: 'italic', fontSize: 'inherit' }}
                            >
                              No email
                            </Typography>
                          )}
                        </TableCell>
                        <TableCell>
                          <Tooltip title="Edit customer" arrow>
                            <IconButton
                              size="small"
                              onClick={() => openEditDialog(customer)}
                            >
                              <EditIcon fontSize="small" />
                            </IconButton>
                          </Tooltip>
                        </TableCell>
                      </TableRow>
                    ))}
                {!isLoading && rows.length === 0 && !isError && (
                  <TableRow>
                    <TableCell colSpan={COL_COUNT} align="center" sx={{ py: 4 }}>
                      <Typography color="text.secondary">
                        {debouncedSearch
                          ? 'No customers match your search.'
                          : 'No customers yet. Click "New Customer" to add one.'}
                      </Typography>
                    </TableCell>
                  </TableRow>
                )}
              </TableBody>
            </Table>
          </TableContainer>

          <TablePagination
            component="div"
            count={totalCount}
            page={page - 1}
            onPageChange={(_, newPage) => setPage(newPage + 1)}
            rowsPerPage={pageSize}
            onRowsPerPageChange={(e) => setPageSize(parseInt(e.target.value, 10))}
            rowsPerPageOptions={[12, 24, 48]}
          />
        </CardContent>
      </Card>

      {/* Create / Edit Dialog */}
      <Dialog open={dialogOpen} onClose={closeDialog} maxWidth="sm" fullWidth>
        <DialogTitle>{isEditing ? 'Edit Customer' : 'New Customer'}</DialogTitle>
        <DialogContent>
          <Box sx={{ display: 'flex', flexDirection: 'column', gap: 2, mt: 1 }}>
            <TextField
              label="Name"
              value={form.name}
              onChange={(e) => handleFieldChange('name', e.target.value)}
              error={!!formErrors.name}
              helperText={formErrors.name}
              size="small"
              required
              fullWidth
              autoFocus
            />
            <TextField
              label="Address"
              value={form.address}
              onChange={(e) => handleFieldChange('address', e.target.value)}
              error={!!formErrors.address}
              helperText={formErrors.address}
              size="small"
              required
              fullWidth
            />
            <TextField
              label="Contact Email"
              type="email"
              value={form.contactEmail}
              onChange={(e) => handleFieldChange('contactEmail', e.target.value)}
              error={!!formErrors.contactEmail}
              helperText={formErrors.contactEmail || 'Optional. Used for proposal PDF delivery.'}
              size="small"
              fullWidth
            />
          </Box>
        </DialogContent>
        <DialogActions>
          <Button onClick={closeDialog} disabled={isSaving}>
            Cancel
          </Button>
          <Button
            variant="contained"
            onClick={handleSubmit}
            disabled={isSaving}
          >
            {isSaving ? (isEditing ? 'Saving...' : 'Creating...') : isEditing ? 'Save Changes' : 'Create Customer'}
          </Button>
        </DialogActions>
      </Dialog>
    </Box>
  );
}