import React, { useState, useMemo, useEffect } from 'react';
import { useTranslation } from 'react-i18next';
import { isToday, isYesterday, parseISO, isValid } from 'date-fns';
import { Loader2, Inbox } from 'lucide-react';
import { ActivityFeed, ActivityItem } from '@/components/shared/ActivityFeed';
import { ActivityFilter, ActivityFilterValues } from '@/components/activity/ActivityFilter';
import { useAuditLog, AuditLogEntry } from '@/api/audit';
import { formatDateTime, formatDate } from '@/utils/date';

const PAGE_SIZE = 25;

interface DayGroup {
  key: string;
  label: string;
  activities: ActivityItem[];
}

function toValidDate(value: string): Date | null {
  if (!value) return null;
  const parsed = parseISO(value);
  return isValid(parsed) ? parsed : null;
}

function getDayLabel(date: Date): string {
  if (isToday(date)) return 'Heute';
  if (isYesterday(date)) return 'Gestern';
  return formatDate(date, 'EEEE, dd.MM.yyyy');
}

function groupByDay(entries: AuditLogEntry[]): DayGroup[] {
  const groups: Map<string, DayGroup> = new Map();

  for (const entry of entries) {
    const date = toValidDate(entry.timestamp);
    if (!date) continue;

    const dayKey = formatDate(date, 'yyyy-MM-dd');
    if (!groups.has(dayKey)) {
      groups.set(dayKey, {
        key: dayKey,
        label: getDayLabel(date),
        activities: [],
      });
    }

    const activity: ActivityItem = {
      id: `${entry.id}-${entry.timestamp}`,
      user: entry.user || 'System',
      action: entry.action || '',
      time: entry.timestamp ? formatDateTime(entry.timestamp) : '',
      avatarUrl: null,
    };
    groups.get(dayKey)!.activities.push(activity);
  }

  return Array.from(groups.values()).sort((a, b) => b.key.localeCompare(a.key));
}

function LoadingSkeleton() {
  return (
    <div className="space-y-4" data-testid="activity-timeline-skeleton">
      {[1, 2, 3].map((i) => (
        <div key={i} className="bg-white rounded-lg shadow-sm border border-secondary-200 p-6">
          <div className="h-5 w-32 bg-secondary-200 rounded animate-pulse mb-4" />
          <div className="space-y-3">
            {[1, 2, 3].map((j) => (
              <div key={j} className="flex items-center gap-3">
                <div className="h-8 w-8 bg-secondary-200 rounded-full animate-pulse" />
                <div className="flex-1 space-y-1">
                  <div className="h-4 w-3/4 bg-secondary-200 rounded animate-pulse" />
                  <div className="h-3 w-1/4 bg-secondary-200 rounded animate-pulse" />
                </div>
              </div>
            ))}
          </div>
        </div>
      ))}
    </div>
  );
}

function EmptyState({ message }: { message: string }) {
  return (
    <div
      className="bg-white rounded-lg shadow-sm border border-secondary-200 p-12 text-center"
      data-testid="activity-timeline-empty"
    >
      <Inbox className="h-12 w-12 text-secondary-300 mx-auto mb-3" aria-hidden="true" />
      <p className="text-sm text-secondary-500">{message}</p>
    </div>
  );
}

export function ActivityTimelinePage() {
  const { t } = useTranslation();
  const [page, setPage] = useState(1);
  const [filters, setFilters] = useState<ActivityFilterValues>({});
  const [accumulated, setAccumulated] = useState<AuditLogEntry[]>([]);

  const apiFilters = useMemo(
    () => ({
      user: filters.user,
      action: filters.action,
      entity: filters.entity_type,
      dateFrom: filters.date_from,
      dateTo: filters.date_to,
    }),
    [filters]
  );

  const { data, isLoading, isError, isFetching } = useAuditLog(page, PAGE_SIZE, apiFilters);

  const entries = data?.items ?? [];
  const total = data?.total ?? 0;
  const hasMore = page * PAGE_SIZE < total;

  useEffect(() => {
    if (page === 1) {
      setAccumulated(entries);
    } else {
      setAccumulated((prev) => {
        const existingIds = new Set(prev.map((e) => e.id));
        const newEntries = entries.filter((e) => !existingIds.has(e.id));
        return [...prev, ...newEntries];
      });
    }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [entries, page]);

  const handleFilterChange = (newFilters: ActivityFilterValues) => {
    setFilters(newFilters);
    setPage(1);
    setAccumulated([]);
  };

  const dayGroups = useMemo(() => groupByDay(accumulated), [accumulated]);

  const pageTitle = t('activity.title', 'Aktivitäten');

  return (
    <div className="p-6 max-w-7xl mx-auto" data-testid="activity-timeline-page">
      <h1 className="text-2xl font-bold text-secondary-900 mb-6">{pageTitle}</h1>

      <ActivityFilter onFilter={handleFilterChange} initialValues={filters} />

      {isLoading && page === 1 ? (
        <LoadingSkeleton />
      ) : isError ? (
        <div
          className="bg-white rounded-lg shadow-sm border border-secondary-200 p-12 text-center"
          data-testid="activity-timeline-error"
        >
          <p className="text-sm text-secondary-500">
            {t('activity.loadError', 'Aktivitäten konnten nicht geladen werden.')}
          </p>
        </div>
      ) : dayGroups.length === 0 ? (
        <EmptyState
          message={t('activity.empty', 'Keine Aktivitäten gefunden.')}
        />
      ) : (
        <>
          <div className="space-y-6">
            {dayGroups.map((group) => (
              <ActivityFeed
                key={group.key}
                activities={group.activities}
                title={group.label}
                maxItems={group.activities.length}
              />
            ))}
          </div>

          {hasMore && (
            <div className="flex justify-center mt-6">
              <button
                type="button"
                onClick={() => setPage((p) => p + 1)}
                disabled={isFetching}
                className="inline-flex items-center justify-center font-medium px-4 py-2 rounded-md min-h-touch bg-primary-600 text-white hover:bg-primary-700 disabled:opacity-50 disabled:cursor-not-allowed transition-colors"
                data-testid="activity-load-more"
              >
                {isFetching ? (
                  <>
                    <Loader2 className="animate-spin h-4 w-4 mr-2" aria-hidden="true" />
                    {t('activity.loading', 'Lädt …')}
                  </>
                ) : (
                  t('activity.loadMore', 'Mehr laden')
                )}
              </button>
            </div>
          )}

          <p className="text-center text-sm text-secondary-400 mt-4">
            {accumulated.length} / {total} {t('activity.entriesLoaded', 'Einträge')}
          </p>
        </>
      )}
    </div>
  );
}