import { useNavigate } from 'react-router-dom';
import { useQuery } from '@tanstack/react-query';
import {
  Box,
  Typography,
  Card,
  CardContent,
  Grid,
  Table,
  TableBody,
  TableCell,
  TableContainer,
  TableHead,
  TableRow,
  Chip,
  Button,
  Skeleton,
  Alert,
} from '@mui/material';
import AddCircleIcon from '@mui/icons-material/AddCircle';
import DescriptionIcon from '@mui/icons-material/Description';
import HourglassTopIcon from '@mui/icons-material/HourglassTop';
import CheckCircleIcon from '@mui/icons-material/CheckCircle';
import SendIcon from '@mui/icons-material/Send';
import ErrorOutlineIcon from '@mui/icons-material/ErrorOutline';
import Tooltip from '@mui/material/Tooltip';
import { proposalsApi, type ProposalListItem, type ProposalStats } from '../../lib/api/proposals';
import { QUERY_KEYS } from '../../constants/queryKeys';
import { STATUS_CHIP_STYLES } from '../../constants';
import { formatCurrency, formatDate, formatDateFull } from '../../lib/format';
import { useDocumentTitle } from '../../hooks/useDocumentTitle';

function KpiCard({ icon, label, value, subtitle }: { icon: React.ReactNode; label: string; value: string; subtitle?: string }) {
  return (
    <Card sx={{ borderRadius: '8px', transition: 'transform 0.2s, box-shadow 0.2s', '&:hover': { transform: 'translateY(-2px)', boxShadow: '0 4px 8px rgba(0,0,0,0.15)' } }}>
      <CardContent sx={{ textAlign: 'center', py: 2.5 }}>
        <Box sx={{ display: 'flex', justifyContent: 'center', mb: 1, color: '#0B5A73' }}>{icon}</Box>
        <Typography sx={{ fontSize: '12px', color: '#64748B', textTransform: 'uppercase', letterSpacing: '0.06em', fontWeight: 600, mb: 1 }}>
          {label}
        </Typography>
        <Typography sx={{ fontSize: '36px', fontWeight: 800, color: '#073B4C', letterSpacing: '-0.03em' }}>
          {value}
        </Typography>
        {subtitle && (
          <Typography sx={{ fontSize: '11px', color: '#94A3B8', fontWeight: 500, marginTop: '4px' }}>
            {subtitle}
          </Typography>
        )}
      </CardContent>
    </Card>
  );
}

export default function Dashboard() {
  useDocumentTitle('Dashboard');
  const navigate = useNavigate();

  const { data: recentData, isLoading: recentLoading, error: recentError } = useQuery<{ items: ProposalListItem[]; totalCount: number }>({
    queryKey: [QUERY_KEYS.proposals, 'dashboard-recent'],
    queryFn: () => proposalsApi.getAll({ page: 1, pageSize: 5, mine: true }),
  });

  // Fix: WEB-M8 — capture error state for stats to show error instead of misleading zeros
  const { data: stats, isLoading: statsLoading, isError: statsError, refetch: refetchStats } = useQuery<ProposalStats>({
    queryKey: [QUERY_KEYS.proposals, 'stats'],
    queryFn: () => proposalsApi.getStats(),
  });

  const proposals = recentData?.items ?? [];
  const total = stats?.totalCount ?? 0;
  const counts = {
    inReview: stats?.inReviewCount ?? 0,
    approved: stats?.approvedCount ?? 0,
    sent: stats?.sentCount ?? 0,
  };

  return (
    <Box>
      <Box sx={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', mb: 2 }}>
        <Typography variant="h5">Dashboard</Typography>
        <Button
          variant="contained"
          startIcon={<AddCircleIcon />}
          onClick={() => navigate('/proposals/new')}
        >
          New Proposal
        </Button>
      </Box>

      {/* Fix: WEB-M8 — show error state instead of misleading zeros when stats fetch fails */}
      <Grid container spacing={2} sx={{ mb: 3 }}>
        {statsError ? (
          <Grid size={{ xs: 12 }}>
            <Alert
              severity="error"
              icon={<ErrorOutlineIcon />}
              action={
                <Button color="inherit" size="small" onClick={() => refetchStats()}>
                  Retry
                </Button>
              }
            >
              Failed to load dashboard statistics. Please try again.
            </Alert>
          </Grid>
        ) : (
          <>
            <Grid size={{ xs: 6, sm: 3 }}>
              {statsLoading ? (
                <Skeleton variant="rectangular" height={120} sx={{ borderRadius: 2 }} />
              ) : (
                <KpiCard icon={<DescriptionIcon fontSize="large" />} label="Total Submitted" value={String(total)} subtitle="All time" />
              )}
            </Grid>
            <Grid size={{ xs: 6, sm: 3 }}>
              {statsLoading ? (
                <Skeleton variant="rectangular" height={120} sx={{ borderRadius: 2 }} />
              ) : (
                <KpiCard icon={<HourglassTopIcon fontSize="large" />} label="In Review" value={String(counts.inReview)} subtitle="Awaiting pricing" />
              )}
            </Grid>
            <Grid size={{ xs: 6, sm: 3 }}>
              {statsLoading ? (
                <Skeleton variant="rectangular" height={120} sx={{ borderRadius: 2 }} />
              ) : (
                <KpiCard icon={<CheckCircleIcon fontSize="large" />} label="Approved" value={String(counts.approved)} subtitle="Ready to send" />
              )}
            </Grid>
            <Grid size={{ xs: 6, sm: 3 }}>
              {statsLoading ? (
                <Skeleton variant="rectangular" height={120} sx={{ borderRadius: 2 }} />
              ) : (
                <KpiCard icon={<SendIcon fontSize="large" />} label="Sent" value={String(counts.sent)} subtitle="Delivered to customer" />
              )}
            </Grid>
          </>
        )}
      </Grid>

      <Card>
        <CardContent sx={{ pb: 1 }}>
          <Box sx={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', mb: 2 }}>
            <Typography variant="h6">Recent Proposals</Typography>
            <Button size="small" onClick={() => navigate('/proposals')}>
              View All
            </Button>
          </Box>

          <TableContainer>
            <Table size="small">
              <TableHead>
                <TableRow>
                  <TableCell>Proposal #</TableCell>
                  <TableCell>Customer</TableCell>
                  <TableCell>Category</TableCell>
                  <TableCell>Status</TableCell>
                  <TableCell align="right">Bid Amount</TableCell>
                  <TableCell>Submitted</TableCell>
                </TableRow>
              </TableHead>
              <TableBody>
                {recentLoading
                  ? Array.from({ length: 5 }).map((_, i) => (
                      <TableRow key={i}>
                        {Array.from({ length: 6 }).map((_, j) => (
                          <TableCell key={j}><Skeleton variant="text" /></TableCell>
                        ))}
                      </TableRow>
                    ))
                  : proposals.map((row) => (
                      <TableRow
                        key={row.id}
                        hover
                        sx={{ cursor: 'pointer' }}
                        onClick={() => navigate(`/proposals/${row.id}`)}
                      >
                        <TableCell sx={{ fontWeight: 600 }}>{row.proposalNumber}</TableCell>
                        <TableCell>{row.customerName}</TableCell>
                        <TableCell>{row.serviceCategory}</TableCell>
                        <TableCell>
                          <Chip label={row.status} size="small" sx={STATUS_CHIP_STYLES[row.status]} />
                        </TableCell>
                        <TableCell align="right">{formatCurrency(row.totalBidAmount)}</TableCell>
                        <TableCell>
                          <Tooltip title={formatDateFull(row.submittedAt)} arrow>
                            <span>{formatDate(row.submittedAt)}</span>
                          </Tooltip>
                        </TableCell>
                      </TableRow>
                    ))}
                {!recentLoading && recentError && (
                  <TableRow>
                    <TableCell colSpan={6} align="center" sx={{ py: 4 }}>
                      <Typography color="error">
                        Failed to load proposals. Please try again.
                      </Typography>
                    </TableCell>
                  </TableRow>
                )}
                {!recentLoading && !recentError && proposals.length === 0 && (
                  <TableRow>
                    <TableCell colSpan={6} align="center" sx={{ py: 4 }}>
                      <Typography color="text.secondary">
                        No proposals yet. Submit your first one!
                      </Typography>
                    </TableCell>
                  </TableRow>
                )}
              </TableBody>
            </Table>
          </TableContainer>
        </CardContent>
      </Card>
    </Box>
  );
}