import { useEffect, useMemo, useState, Fragment } from 'react';
import { useNavigate } from 'react-router-dom';
import {
  Box,
  Typography,
  Card,
  CardContent,
  Grid,
  Table,
  TableBody,
  TableCell,
  TableContainer,
  TableHead,
  TableRow,
  TablePagination,
  Chip,
  TextField,
  InputAdornment,
  MenuItem,
  Button,
  Skeleton,
  Tabs,
  Tab,
  Collapse,
  IconButton,
  Tooltip,
  Alert,
} from '@mui/material';
import SearchIcon from '@mui/icons-material/Search';
import PendingActionsIcon from '@mui/icons-material/PendingActions';
import CheckCircleIcon from '@mui/icons-material/CheckCircle';
import TimerIcon from '@mui/icons-material/Timer';
import DescriptionIcon from '@mui/icons-material/Description';
import WarningAmberIcon from '@mui/icons-material/WarningAmber';
import ReportIcon from '@mui/icons-material/Report';
import ErrorOutlineIcon from '@mui/icons-material/ErrorOutlined';
import KeyboardArrowDownIcon from '@mui/icons-material/KeyboardArrowDown';
import KeyboardArrowRightIcon from '@mui/icons-material/KeyboardArrowRight';
import { useProposals } from '../../../domain/proposals/use-cases';
import type { ProposalListItem } from '../../../domain/proposals/types';
import { useAdminDashboard } from '../../../domain/admin/use-cases';
import { DEBOUNCE_SEARCH, DEFAULT_PAGE, DEFAULT_PAGE_SIZE, SERVICE_CATEGORIES, PRIORITIES, PROPOSAL_STATUSES, STATUS_CHIP_STYLES, STATUS_LABELS, PRIORITY_LABELS, PRIORITY_CHIP_STYLES, PRIORITY_ROW_SX } from '../../../constants';
import { formatBidAmount, formatDate, formatDateFull, formatAge, getAgeColor, groupRevisions } from '../../../lib/format';
import { useDocumentTitle } from '../../../hooks/useDocumentTitle';

const COL_COUNT = 11;
const TAB_STATUSES = ['', 'InReview', 'Approved', 'Sent', 'Revised'] as const;

function StatCard({ icon, label, value, color, subtitle }: { icon: React.ReactNode; label: string; value: string; color: string; subtitle?: string }) {
  return (
    <Card sx={{ borderRadius: '8px', transition: 'border-color 120ms ease', '&:hover': { borderColor: '#9CA3AF' } }}>
      <CardContent sx={{ textAlign: 'center', py: 2.5 }}>
        <Box sx={{ color, display: 'flex', justifyContent: 'center', mb: 1 }}>{icon}</Box>
        <Typography sx={{ fontSize: '12px', color: '#64748B', textTransform: 'uppercase', letterSpacing: '0.06em', fontWeight: 600, mb: 1 }}>
          {label}
        </Typography>
        <Typography sx={{ fontSize: '30px', fontWeight: 700, color: 'var(--foreground)', letterSpacing: '-0.02em' }}>
          {value}
        </Typography>
        {subtitle && (
          <Typography sx={{ fontSize: '11px', color: '#94A3B8', fontWeight: 500, marginTop: '4px' }}>
            {subtitle}
          </Typography>
        )}
      </CardContent>
    </Card>
  );
}

export default function AdminDashboard({ defaultStatus }: { defaultStatus?: string }) {
  useDocumentTitle(defaultStatus ? 'Admin Queue' : 'Admin Dashboard');
  const navigate = useNavigate();
  const showTabs = !defaultStatus;

  // Fix: WEB-M8 — capture error state for admin stats to show error instead of misleading zeros
  const { data: stats, isLoading: statsLoading, isError: statsError, refetch: refetchStats } = useAdminDashboard();

  const [statusFilter, setStatusFilter] = useState(defaultStatus ?? '');
  const [categoryFilter, setCategoryFilter] = useState('');
  const [priorityFilter, setPriorityFilter] = useState('');
  const [expanded, setExpanded] = useState<Set<string>>(new Set());

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

  // Debounced search resets to page 1 (mirrors the old usePaginatedList behavior).
  useEffect(() => {
    const handle = setTimeout(() => {
      setDebouncedSearch(search);
      setPage(1);
    }, DEBOUNCE_SEARCH);
    return () => clearTimeout(handle);
  }, [search]);

  const {
    data: listData,
    isPending: listPending,
    isPlaceholderData: listIsPlaceholder,
    error: listError,
  } = useProposals({
    search: debouncedSearch,
    page,
    pageSize,
    ...(statusFilter && { status: statusFilter }),
    ...(categoryFilter && { serviceCategory: categoryFilter }),
    ...(priorityFilter && { priority: priorityFilter }),
  });

  const rows = useMemo(() => listData?.items ?? [], [listData]);
  const totalCount = listData?.totalCount ?? 0;
  // Show skeletons on initial load and while previous-page placeholder data is
  // displayed for a new filter/page/search key (matches the old loading flag).
  const loading = listPending || listIsPlaceholder;
  const err = listError ? listError.message || 'Failed to load' : '';

  const grouped = useMemo(() => groupRevisions(rows), [rows]);

  const toggleExpand = (baseNumber: string) => {
    setExpanded((prev) => {
      const next = new Set(prev);
      if (next.has(baseNumber)) next.delete(baseNumber);
      else next.add(baseNumber);
      return next;
    });
  };

  const tabIndex = TAB_STATUSES.indexOf(statusFilter as typeof TAB_STATUSES[number]);

  const handleTabChange = (_: React.SyntheticEvent, newValue: number) => {
    setStatusFilter(TAB_STATUSES[newValue] ?? '');
    setPage(1);
  };

  const hasActiveFilters = statusFilter || categoryFilter || priorityFilter || search;

  const clearFilters = () => {
    setStatusFilter(defaultStatus ?? '');
    setCategoryFilter('');
    setPriorityFilter('');
    setSearch('');
    setPage(1);
  };

  const renderRow = (row: ProposalListItem, indent: boolean, showExpandIcon: boolean, isExpanded: boolean, baseNumber: string) => (
    <TableRow
      key={row.id}
      hover
      sx={{
        cursor: 'pointer',
        ...PRIORITY_ROW_SX[row.priority],
        ...(indent && { bgcolor: 'action.hover' }),
      }}
      onClick={() => navigate(`/admin/proposals/${row.id}`)}
    >
      <TableCell sx={{ width: 40, px: 1 }}>
        {showExpandIcon && (
          <IconButton
            size="small"
            onClick={(e) => {
              e.stopPropagation();
              toggleExpand(baseNumber);
            }}
          >
            {isExpanded ? <KeyboardArrowDownIcon fontSize="small" /> : <KeyboardArrowRightIcon fontSize="small" />}
          </IconButton>
        )}
      </TableCell>
      <TableCell sx={{ fontWeight: 600, ...(indent && { pl: 5 }) }}>{row.proposalNumber}</TableCell>
      <TableCell>{row.customerName}</TableCell>
      <TableCell>{row.workOrderNumber}</TableCell>
      <TableCell>{row.serviceCategory}</TableCell>
      <TableCell>
        <Chip
          label={PRIORITY_LABELS[row.priority] || row.priority}
          size="small"
          sx={{ ...PRIORITY_CHIP_STYLES[row.priority], '& .MuiChip-icon': { color: 'inherit' } }}
          icon={row.priority === 'Emergency' ? <ReportIcon /> : row.priority === 'Urgent' ? <WarningAmberIcon /> : undefined}
        />
      </TableCell>
      <TableCell>
        <Chip label={STATUS_LABELS[row.status] || row.status} size="small" sx={STATUS_CHIP_STYLES[row.status]} />
      </TableCell>
      <TableCell align="right">{formatBidAmount(row.totalBidAmount)}</TableCell>
      <TableCell>
        <Tooltip title={formatDateFull(row.submittedAt)} arrow>
          <span>{formatDate(row.submittedAt)}</span>
        </Tooltip>
      </TableCell>
      <TableCell>{row.submittedByName || '-'}</TableCell>
      <TableCell sx={{ color: getAgeColor(row.submittedAt), fontWeight: getAgeColor(row.submittedAt) ? 600 : undefined }}>
        {formatAge(row.submittedAt)}
      </TableCell>
    </TableRow>
  );

  return (
    <Box>
      <Typography variant="h5" sx={{ mb: 3 }}>{defaultStatus ? 'Admin Queue' : 'All Proposals'}</Typography>

      {/* 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: 12, sm: 6, md: 3 }}>
              {statsLoading ? (
                <Skeleton variant="rectangular" height={80} sx={{ borderRadius: 1 }} />
              ) : (
                <StatCard
                  icon={<PendingActionsIcon fontSize="large" />}
                  label="Pending Review"
                  value={String(stats?.pendingCount ?? 0)}
                  color="#1565c0"
                  subtitle="Awaiting action"
                />
              )}
            </Grid>
            <Grid size={{ xs: 12, sm: 6, md: 3 }}>
              {statsLoading ? (
                <Skeleton variant="rectangular" height={80} sx={{ borderRadius: 1 }} />
              ) : (
                <StatCard
                  icon={<CheckCircleIcon fontSize="large" />}
                  label="Approved This Week"
                  value={String(stats?.approvedThisWeek ?? 0)}
                  color="#2e7d32"
                  subtitle={`${stats?.approvedThisWeek ?? 0} approved`}
                />
              )}
            </Grid>
            <Grid size={{ xs: 12, sm: 6, md: 3 }}>
              {statsLoading ? (
                <Skeleton variant="rectangular" height={80} sx={{ borderRadius: 1 }} />
              ) : (
                <StatCard
                  icon={<TimerIcon fontSize="large" />}
                  label="Avg Turnaround"
                  value={stats ? `${Math.round(stats.avgTurnaroundHours)}h` : '-'}
                  color="#f57c00"
                  subtitle="Target: <24h"
                />
              )}
            </Grid>
            <Grid size={{ xs: 12, sm: 6, md: 3 }}>
              {statsLoading ? (
                <Skeleton variant="rectangular" height={80} sx={{ borderRadius: 1 }} />
              ) : (
                <StatCard
                  icon={<DescriptionIcon fontSize="large" />}
                  label="Total Proposals"
                  value={String(stats?.totalProposals ?? 0)}
                  color="#5e35b1"
                  subtitle="All time"
                />
              )}
            </Grid>
          </>
        )}
      </Grid>

      <Card>
        <CardContent sx={{ pb: 0 }}>
          {showTabs && (
            <Tabs
              value={tabIndex >= 0 ? tabIndex : 0}
              onChange={handleTabChange}
              sx={{ mb: 2, borderBottom: 1, borderColor: 'divider' }}
            >
              <Tab label="All" />
              {TAB_STATUSES.slice(1).map((s) => (
                <Tab key={s} label={STATUS_LABELS[s] ?? s} />
              ))}
            </Tabs>
          )}

          <Box sx={{ display: 'flex', gap: 2, mb: 2, flexWrap: 'wrap' }}>
            <TextField
              size="small"
              placeholder="Search..."
              value={search}
              onChange={(e) => setSearch(e.target.value)}
              sx={{ width: 240 }}
              slotProps={{
                input: {
                  startAdornment: (
                    <InputAdornment position="start">
                      <SearchIcon fontSize="small" />
                    </InputAdornment>
                  ),
                },
              }}
            />
            <TextField
              size="small"
              select
              label="Category"
              value={categoryFilter}
              sx={{ width: 160 }}
              onChange={(e) => {
                setCategoryFilter(e.target.value);
                setPage(1);
              }}
            >
              <MenuItem value="">All</MenuItem>
              {SERVICE_CATEGORIES.map((c) => (
                <MenuItem key={c} value={c}>{c}</MenuItem>
              ))}
            </TextField>
            <TextField
              size="small"
              select
              label="Priority"
              value={priorityFilter}
              sx={{ width: 200 }}
              onChange={(e) => {
                setPriorityFilter(e.target.value);
                setPage(1);
              }}
            >
              <MenuItem value="">All</MenuItem>
              {PRIORITIES.map((p) => (
                <MenuItem key={p} value={p}>{PRIORITY_LABELS[p] || p}</MenuItem>
              ))}
            </TextField>
            {!showTabs && (
              <TextField
                size="small"
                select
                label="Status"
                value={statusFilter}
                sx={{ width: 140 }}
                onChange={(e) => {
                  setStatusFilter(e.target.value);
                  setPage(1);
                }}
              >
                <MenuItem value="">All</MenuItem>
                {PROPOSAL_STATUSES.map((s) => (
                  <MenuItem key={s} value={s}>{STATUS_LABELS[s] || s}</MenuItem>
                ))}
              </TextField>
            )}
            {hasActiveFilters && (
              <Button size="small" onClick={clearFilters}>
                Clear Filters
              </Button>
            )}
          </Box>

          {err && (
            <Typography color="error" sx={{ mb: 2 }}>{err}</Typography>
          )}

          <TableContainer>
            <Table size="small">
              <TableHead>
                <TableRow>
                  <TableCell sx={{ width: 40, px: 1 }} />
                  <TableCell>Proposal #</TableCell>
                  <TableCell>Customer</TableCell>
                  <TableCell>WO #</TableCell>
                  <TableCell>Category</TableCell>
                  <TableCell>Priority</TableCell>
                  <TableCell>Status</TableCell>
                  <TableCell align="right">Bid Amount</TableCell>
                  <TableCell>Submitted</TableCell>
                  <TableCell>Submitted By</TableCell>
                  <TableCell>Age</TableCell>
                </TableRow>
              </TableHead>
              <TableBody>
                {loading
                  ? Array.from({ length: 5 }).map((_, i) => (
                      <TableRow key={i}>
                        {Array.from({ length: COL_COUNT }).map((_, j) => (
                          <TableCell key={j}><Skeleton variant="text" /></TableCell>
                        ))}
                      </TableRow>
                    ))
                  : grouped.map((group) => {
                      const isExpanded = expanded.has(group.baseNumber);
                      return (
                        <Fragment key={group.baseNumber}>
                          {renderRow(group.latest, false, group.hasRevisions, isExpanded, group.baseNumber)}
                          {group.hasRevisions && (
                            <TableRow>
                              <TableCell colSpan={COL_COUNT} sx={{ p: 0, border: 0 }}>
                                <Collapse in={isExpanded} timeout="auto" unmountOnExit>
                                  <Table size="small">
                                    <TableBody>
                                      {group.revisions.map((rev) =>
                                        renderRow(rev, true, false, false, group.baseNumber)
                                      )}
                                    </TableBody>
                                  </Table>
                                </Collapse>
                              </TableCell>
                            </TableRow>
                          )}
                        </Fragment>
                      );
                    })}
                {!loading && rows.length === 0 && (
                  <TableRow>
                    <TableCell colSpan={COL_COUNT} align="center" sx={{ py: 4 }}>
                      <Typography color="text.secondary" sx={{ mb: 1 }}>
                        {hasActiveFilters
                          ? 'No proposals match your current filters.'
                          : 'No proposals in queue.'}
                      </Typography>
                      {hasActiveFilters && (
                        <Button size="small" onClick={clearFilters}>
                          Clear Filters
                        </Button>
                      )}
                    </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>
    </Box>
  );
}