import React, { useState, useEffect, useMemo, useCallback } from 'react';
import { useTranslation } from 'react-i18next';
import {
  DndContext,
  closestCenter,
  KeyboardSensor,
  PointerSensor,
  useSensor,
  useSensors,
  DragEndEvent,
} from '@dnd-kit/core';
import {
  arrayMove,
  SortableContext,
  sortableKeyboardCoordinates,
  verticalListSortingStrategy,
} from '@dnd-kit/sortable';
import { SortableMenuItem } from '@/components/layout/SortableMenuItem';
import { Button } from '@/components/ui/Button';
import { Card } from '@/components/ui/Card';
import { Skeleton } from '@/components/ui/Skeleton';
import { useToast } from '@/components/ui/Toast';
import { usePluginStore, PluginMenuItem } from '@/store/pluginStore';
import { useMenuOrder, useUpdateMenuOrder } from '@/api/users';
import { GripVertical, RotateCcw, Save } from 'lucide-react';

interface MenuEntry {
  id: string;
  label: string;
  icon: string;
  isGroup?: boolean;
}

const DEFAULT_ORDER = [
  'dashboard',
  'contacts',
  'calendar',
  'mail',
  'tasks',
  'dms',
  'automation',
  'reports',
  'communication',
  'ai-assistant',
  'settings',
];

export function SettingsMenuOrderPage() {
  const { t } = useTranslation();
  const toast = useToast();
  const manifests = usePluginStore((s) => s.manifests);
  const { data: menuOrderData, isLoading: orderLoading } = useMenuOrder();
  const updateMutation = useUpdateMenuOrder();

  const [items, setItems] = useState<MenuEntry[]>([]);

  const pluginMenuItems = useMemo(
    () => manifests
      .flatMap((m) => m.menu_items)
      .sort((a, b) => a.order - b.order),
    [manifests]
  );

  // Build all menu entries from static + plugin items
  const allEntries = useMemo(() => {
    const entries: MenuEntry[] = [];

    // Static entries
    entries.push({ id: 'dashboard', label: t('nav.dashboard'), icon: 'Home' });
    entries.push({ id: 'contacts', label: t('nav.contacts'), icon: 'Users' });

    // Plugin entries
    const groups = new Map<string, PluginMenuItem[]>();
    const singles: PluginMenuItem[] = [];
    for (const item of pluginMenuItems) {
      if (item.group) {
        if (!groups.has(item.group)) groups.set(item.group, []);
        groups.get(item.group)!.push(item);
      } else {
        singles.push(item);
      }
    }

    for (const item of singles) {
      entries.push({
        id: item.path,
        label: t(item.label_key, item.label),
        icon: item.icon,
      });
    }

    for (const [group, groupItems] of groups) {
      entries.push({
        id: group,
        label: group,
        icon: groupItems[0].icon,
        isGroup: true,
      });
    }

    // Settings at the end
    entries.push({ id: 'settings', label: t('nav.settings'), icon: 'Settings' });

    return entries;
  }, [pluginMenuItems, t]);

  // Apply saved order or default
  useEffect(() => {
    if (orderLoading) return;
    const savedOrder = menuOrderData?.menu_order;
    if (savedOrder && savedOrder.length > 0) {
      // Sort entries by saved order, keeping any new entries at the end
      const orderMap = new Map(savedOrder.map((id, idx) => [id, idx]));
      const sorted = [...allEntries].sort((a, b) => {
        const aIdx = orderMap.get(a.id);
        const bIdx = orderMap.get(b.id);
        if (aIdx !== undefined && bIdx !== undefined) return aIdx - bIdx;
        if (aIdx !== undefined) return -1;
        if (bIdx !== undefined) return 1;
        return 0;
      });
      setItems(sorted);
    } else {
      // Use default order
      const orderMap = new Map(DEFAULT_ORDER.map((id, idx) => [id, idx]));
      const sorted = [...allEntries].sort((a, b) => {
        const aIdx = orderMap.get(a.id);
        const bIdx = orderMap.get(b.id);
        if (aIdx !== undefined && bIdx !== undefined) return aIdx - bIdx;
        if (aIdx !== undefined) return -1;
        if (bIdx !== undefined) return 1;
        return 0;
      });
      setItems(sorted);
    }
  }, [allEntries, menuOrderData, orderLoading]);

  const sensors = useSensors(
    useSensor(PointerSensor, {
      activationConstraint: { distance: 8 },
    }),
    useSensor(KeyboardSensor, {
      coordinateGetter: sortableKeyboardCoordinates,
    })
  );

  const handleDragEnd = useCallback((event: DragEndEvent) => {
    const { active, over } = event;
    if (!over || active.id === over.id) return;

    setItems((prev) => {
      const oldIndex = prev.findIndex((item) => item.id === active.id);
      const newIndex = prev.findIndex((item) => item.id === over.id);
      if (oldIndex === -1 || newIndex === -1) return prev;
      return arrayMove(prev, oldIndex, newIndex);
    });
  }, []);

  const handleSave = async () => {
    try {
      const order = items.map((item) => item.id);
      await updateMutation.mutateAsync(order);
      toast.success(t('settings.saved', 'Gespeichert'));
    } catch (err: any) {
      toast.error(err.message || t('settings.saveFailed', 'Speichern fehlgeschlagen'));
    }
  };

  const handleReset = () => {
    const orderMap = new Map(DEFAULT_ORDER.map((id, idx) => [id, idx]));
    const sorted = [...allEntries].sort((a, b) => {
      const aIdx = orderMap.get(a.id);
      const bIdx = orderMap.get(b.id);
      if (aIdx !== undefined && bIdx !== undefined) return aIdx - bIdx;
      if (aIdx !== undefined) return -1;
      if (bIdx !== undefined) return 1;
      return 0;
    });
    setItems(sorted);
  };

  if (orderLoading) {
    return (
      <div className="space-y-4" data-testid="settings-menu-order-page">
        <Skeleton className="h-8 w-48" />
        <Skeleton className="h-96" />
      </div>
    );
  }

  return (
    <div className="space-y-6" data-testid="settings-menu-order-page">
      <div className="flex items-center justify-between">
        <h1 className="text-2xl font-bold text-secondary-900">
          {t('settings.menuOrder', 'Menü-Reihenfolge')}
        </h1>
        <div className="flex gap-2">
          <Button variant="secondary" onClick={handleReset}>
            <RotateCcw className="w-4 h-4 mr-2" />
            {t('settings.reset', 'Zurücksetzen')}
          </Button>
          <Button onClick={handleSave} disabled={updateMutation.isPending}>
            <Save className="w-4 h-4 mr-2" />
            {t('settings.save', 'Speichern')}
          </Button>
        </div>
      </div>

      <Card>
        <p className="text-sm text-secondary-500 mb-4 px-4 pt-4">
          {t('settings.menuOrderHint', 'Ziehen Sie die Menü-Einträge per Drag & Drop in die gewünschte Reihenfolge.')}
        </p>
        <DndContext
          sensors={sensors}
          collisionDetection={closestCenter}
          onDragEnd={handleDragEnd}
        >
          <SortableContext
            items={items.map((item) => item.id)}
            strategy={verticalListSortingStrategy}
          >
            <div className="px-4 pb-4 space-y-1">
              {items.map((item) => (
                <SortableMenuItem
                  key={item.id}
                  id={item.id}
                  label={item.label}
                  icon={item.icon}
                  isGroup={item.isGroup}
                />
              ))}
            </div>
          </SortableContext>
        </DndContext>
      </Card>
    </div>
  );
}