import React, { useCallback, useMemo, useEffect, useState, useRef } from 'react';
import { GroupedVirtuoso } from 'react-virtuoso';
import {
  DndContext,
  DragOverlay,
  PointerSensor,
  useSensor,
  useSensors,
  KeyboardSensor,
  TouchSensor,
  closestCenter,
} from '@dnd-kit/core';
import {
  SortableContext,
  verticalListSortingStrategy,
  sortableKeyboardCoordinates,
} from '@dnd-kit/sortable';
import { useTranslation } from 'react-i18next';
import { useParams } from 'react-router-dom';
import { createPortal } from 'react-dom';
import { Skeleton } from 'antd';
import { HolderOutlined } from '@ant-design/icons';

// Redux hooks and selectors
import { useAppSelector } from '@/hooks/useAppSelector';
import { useAppDispatch } from '@/hooks/useAppDispatch';
import {
  selectAllTasksArray,
  selectGroups,
  selectGrouping,
  selectLoading,
  selectError,
  fetchTasksV3,
  fetchTaskListColumns,
  selectColumns,
  selectCustomColumns,
  selectLoadingColumns,
  updateColumnVisibility,
} from '@/features/task-management/task-management.slice';
import {
  selectCurrentGrouping,
  selectCollapsedGroups,
  toggleGroupCollapsed,
} from '@/features/task-management/grouping.slice';
import {
  selectSelectedTaskIds,
  selectLastSelectedTaskId,
  selectTask,
  toggleTaskSelection,
  selectRange,
  clearSelection,
} from '@/features/task-management/selection.slice';
import {
  setCustomColumnModalAttributes,
  toggleCustomColumnModalOpen,
} from '@/features/projects/singleProject/task-list-custom-columns/task-list-custom-columns-slice';

// Components
import TaskRowWithSubtasks from './TaskRowWithSubtasks';
import TaskGroupHeader from './TaskGroupHeader';
import ImprovedTaskFilters from '@/components/task-management/improved-task-filters';
import OptimizedBulkActionBar from '@/components/task-management/optimized-bulk-action-bar';
import CustomColumnModal from '@/pages/projects/projectView/taskList/task-list-table/custom-columns/custom-column-modal/custom-column-modal';
import AddTaskRow from './components/AddTaskRow';
import {
  AddCustomColumnButton,
  CustomColumnHeader,
} from './components/CustomColumnComponents';

// Hooks and utilities
import { useTaskSocketHandlers } from '@/hooks/useTaskSocketHandlers';
import { useSocket } from '@/socket/socketContext';
import { useDragAndDrop } from './hooks/useDragAndDrop';
import { useBulkActions } from './hooks/useBulkActions';

// Constants and types
import { BASE_COLUMNS, ColumnStyle } from './constants/columns';
import { Task } from '@/types/task-management.types';
import { SocketEvents } from '@/shared/socket-events';

const TaskListV2: React.FC = () => {
  const dispatch = useAppDispatch();
  const { projectId: urlProjectId } = useParams();
  const { t } = useTranslation('task-list-table');
  const { socket, connected } = useSocket();

  // Redux state selectors
  const allTasks = useAppSelector(selectAllTasksArray);
  const groups = useAppSelector(selectGroups);
  const grouping = useAppSelector(selectGrouping);
  const loading = useAppSelector(selectLoading);
  const error = useAppSelector(selectError);
  const currentGrouping = useAppSelector(selectCurrentGrouping);
  const selectedTaskIds = useAppSelector(selectSelectedTaskIds);
  const lastSelectedTaskId = useAppSelector(selectLastSelectedTaskId);
  const collapsedGroups = useAppSelector(selectCollapsedGroups);

  const fields = useAppSelector(state => state.taskManagementFields) || [];
  const columns = useAppSelector(selectColumns);
  const customColumns = useAppSelector(selectCustomColumns);
  const loadingColumns = useAppSelector(selectLoadingColumns);

  // Refs for scroll synchronization
  const headerScrollRef = useRef<HTMLDivElement>(null);
  const contentScrollRef = useRef<HTMLDivElement>(null);

  // State hooks
  const [initializedFromDatabase, setInitializedFromDatabase] = useState(false);

  // Configure sensors for drag and drop
  const sensors = useSensors(
    useSensor(PointerSensor, {
      activationConstraint: {
        distance: 8,
      },
    }),
    useSensor(KeyboardSensor, {
      coordinateGetter: sortableKeyboardCoordinates,
    }),
    useSensor(TouchSensor, {
      activationConstraint: {
        delay: 250,
        tolerance: 5,
      },
    })
  );

  // Custom hooks
  const { activeId, handleDragStart, handleDragOver, handleDragEnd } = useDragAndDrop(allTasks, groups);
  const bulkActions = useBulkActions();

  // Enable real-time updates via socket handlers
  useTaskSocketHandlers();

  // Filter visible columns based on local fields (primary) and backend columns (fallback)
  const visibleColumns = useMemo(() => {
    // Start with base columns
    const baseVisibleColumns = BASE_COLUMNS.filter(column => {
      // Always show drag handle and title (sticky columns)
      if (column.isSticky) return true;
      
      // Primary: Check local fields configuration
      const field = fields.find(f => f.key === column.key);
      if (field) {
        return field.visible;
      }
      
      // Fallback: Check backend column configuration if local field not found
      const backendColumn = columns.find(c => c.key === column.key);
      if (backendColumn) {
        return backendColumn.pinned ?? false;
      }
      
      // Default: hide if neither local field nor backend column found
      return false;
    });

    // Add visible custom columns
    const visibleCustomColumns = customColumns
      ?.filter(column => column.pinned)
      ?.map(column => {
        // Give selection columns more width for dropdown content
        const fieldType = column.custom_column_obj?.fieldType;
        let defaultWidth = 160;
        if (fieldType === 'selection') {
          defaultWidth = 150; // Reduced width for selection dropdowns
        } else if (fieldType === 'people') {
          defaultWidth = 170; // Extra width for people with avatars
        }
        
        // Map the configuration data structure to the expected format
        const customColumnObj = column.custom_column_obj || (column as any).configuration;
        
        // Transform configuration format to custom_column_obj format if needed
        let transformedColumnObj = customColumnObj;
        if (customColumnObj && !customColumnObj.fieldType && customColumnObj.field_type) {
          transformedColumnObj = {
            ...customColumnObj,
            fieldType: customColumnObj.field_type,
            numberType: customColumnObj.number_type,
            labelPosition: customColumnObj.label_position,
            previewValue: customColumnObj.preview_value,
            firstNumericColumn: customColumnObj.first_numeric_column_key,
            secondNumericColumn: customColumnObj.second_numeric_column_key,
            selectionsList: customColumnObj.selections_list || customColumnObj.selectionsList || [],
            labelsList: customColumnObj.labels_list || customColumnObj.labelsList || [],
          };
        }
        
        return {
          id: column.key || column.id || 'unknown',
          label: column.name || t('customColumns.customColumnHeader'),
          width: `${(column as any).width || defaultWidth}px`,
          key: column.key || column.id || 'unknown',
          custom_column: true,
          custom_column_obj: transformedColumnObj,
          isCustom: true,
          name: column.name,
          uuid: column.id,
        };
      }) || [];

    return [...baseVisibleColumns, ...visibleCustomColumns];
  }, [fields, columns, customColumns, t]);

  // Effects
  useEffect(() => {
    if (urlProjectId) {
      dispatch(fetchTasksV3(urlProjectId));
      dispatch(fetchTaskListColumns(urlProjectId));
    }
  }, [dispatch, urlProjectId]);

  // Initialize field visibility from database when columns are loaded (only once)
  useEffect(() => {
    if (columns.length > 0 && fields.length > 0 && !initializedFromDatabase) {
      // Update local fields to match database state only on initial load
      import('@/features/task-management/taskListFields.slice').then(({ setFields }) => {
        // Create updated fields based on database column state
        const updatedFields = fields.map(field => {
          const backendColumn = columns.find(c => c.key === field.key);
          if (backendColumn) {
            return {
              ...field,
              visible: backendColumn.pinned ?? field.visible
            };
          }
          return field;
        });
        
        // Only update if there are actual changes
        const hasChanges = updatedFields.some((field, index) => 
          field.visible !== fields[index].visible
        );
        
        if (hasChanges) {
          dispatch(setFields(updatedFields));
        }
        
        setInitializedFromDatabase(true);
      });
    }
  }, [columns, fields, dispatch, initializedFromDatabase]);

  // Event handlers
  const handleTaskSelect = useCallback(
    (taskId: string, event: React.MouseEvent) => {
      if (event.ctrlKey || event.metaKey) {
        dispatch(toggleTaskSelection(taskId));
      } else if (event.shiftKey && lastSelectedTaskId) {
        const taskIds = allTasks.map(t => t.id);
        const startIdx = taskIds.indexOf(lastSelectedTaskId);
        const endIdx = taskIds.indexOf(taskId);
        const rangeIds = taskIds.slice(Math.min(startIdx, endIdx), Math.max(startIdx, endIdx) + 1);
        dispatch(selectRange(rangeIds));
      } else {
        dispatch(clearSelection());
        dispatch(selectTask(taskId));
      }
    },
    [dispatch, lastSelectedTaskId, allTasks]
  );

  const handleGroupCollapse = useCallback(
    (groupId: string) => {
      dispatch(toggleGroupCollapsed(groupId));
    },
    [dispatch]
  );

  // Function to update custom column values
  const updateTaskCustomColumnValue = useCallback((taskId: string, columnKey: string, value: string) => {
    try {
      if (!urlProjectId) {
        console.error('Project ID is missing');
        return;
      }

      const body = {
        task_id: taskId,
        column_key: columnKey,
        value: value,
        project_id: urlProjectId,
      };

      // Update the Redux store immediately for optimistic updates
      const currentTask = allTasks.find(task => task.id === taskId);
      if (currentTask) {
        const updatedTask = {
          ...currentTask,
          custom_column_values: {
            ...currentTask.custom_column_values,
            [columnKey]: value,
          },
          updated_at: new Date().toISOString(),
        };
        
        // Import and dispatch the updateTask action
        import('@/features/task-management/task-management.slice').then(({ updateTask }) => {
          dispatch(updateTask(updatedTask));
        });
      }

      if (socket && connected) {
        socket.emit(SocketEvents.TASK_CUSTOM_COLUMN_UPDATE.toString(), JSON.stringify(body));
      } else {
        console.warn('Socket not connected, unable to emit TASK_CUSTOM_COLUMN_UPDATE event');
      }
    } catch (error) {
      console.error('Error updating custom column value:', error);
    }
  }, [urlProjectId, socket, connected, allTasks, dispatch]);

  // Custom column settings handler
  const handleCustomColumnSettings = useCallback((columnKey: string) => {
    if (!columnKey) return;
    
    const columnData = visibleColumns.find(col => col.key === columnKey || col.id === columnKey);
    
    // Use the UUID for API calls, not the key (nanoid)
    // For custom columns, prioritize the uuid field over id field
    const columnId = (columnData as any)?.uuid || columnData?.id || columnKey;
    
    dispatch(setCustomColumnModalAttributes({ 
      modalType: 'edit', 
      columnId: columnId,
      columnData: columnData
    }));
    dispatch(toggleCustomColumnModalOpen(true));
  }, [dispatch, visibleColumns]);

  // Add callback for task added
  const handleTaskAdded = useCallback(() => {
    // Task is now added in real-time via socket, no need to refetch
    // The global socket handler will handle the real-time update
  }, []);

  // Handle scroll synchronization - disabled since header is now sticky inside content
  const handleContentScroll = useCallback(() => {
    // No longer needed since header scrolls naturally with content
  }, []);

  // Memoized values for GroupedVirtuoso
  const virtuosoGroups = useMemo(() => {
    let currentTaskIndex = 0;

    return groups.map(group => {
      const isCurrentGroupCollapsed = collapsedGroups.has(group.id);

      const visibleTasksInGroup = isCurrentGroupCollapsed
        ? []
        : group.taskIds
            .map(taskId => allTasks.find(task => task.id === taskId))
            .filter((task): task is Task => task !== undefined);

      const tasksForVirtuoso = visibleTasksInGroup.map(task => ({
        ...task,
        originalIndex: allTasks.indexOf(task),
      }));

      const itemsWithAddTask = !isCurrentGroupCollapsed ? [
        ...tasksForVirtuoso,
        {
          id: `add-task-${group.id}`,
          isAddTaskRow: true,
          groupId: group.id,
          groupType: currentGrouping || 'status',
          groupValue: group.id, // Use the actual database ID from backend
          projectId: urlProjectId,
        }
      ] : tasksForVirtuoso;

      const groupData = {
        ...group,
        tasks: itemsWithAddTask,
        startIndex: currentTaskIndex,
        count: itemsWithAddTask.length,
        actualCount: group.taskIds.length,
        groupValue: group.groupValue || group.title,
      };
      currentTaskIndex += itemsWithAddTask.length;
      return groupData;
    });
  }, [groups, allTasks, collapsedGroups, currentGrouping, urlProjectId]);

  const virtuosoGroupCounts = useMemo(() => {
    return virtuosoGroups.map(group => group.count);
  }, [virtuosoGroups]);

  const virtuosoItems = useMemo(() => {
    return virtuosoGroups.flatMap(group => group.tasks);
  }, [virtuosoGroups]);

  // Render functions
  const renderGroup = useCallback(
    (groupIndex: number) => {
      const group = virtuosoGroups[groupIndex];
      const isGroupCollapsed = collapsedGroups.has(group.id);
      const isGroupEmpty = group.actualCount === 0;



      return (
        <div className={groupIndex > 0 ? 'mt-2' : ''}>
          <TaskGroupHeader
            group={{
              id: group.id,
              name: group.title,
              count: group.actualCount,
              color: group.color,
            }}
            isCollapsed={isGroupCollapsed}
            onToggle={() => handleGroupCollapse(group.id)}
            projectId={urlProjectId || ''}
          />
          {isGroupEmpty && !isGroupCollapsed && (
            <div className="relative w-full">
              <div className="flex items-center min-w-max px-1 py-3">
                {visibleColumns.map((column, index) => (
                  <div
                    key={`empty-${column.id}`}
                    style={{ width: column.width, flexShrink: 0 }}
                  />
                ))}
              </div>
              <div className="absolute inset-0 flex items-center justify-center">
                <div className="text-sm italic text-gray-400 dark:text-gray-500 bg-white dark:bg-gray-900 px-4 py-1 rounded-md border border-gray-200 dark:border-gray-700">
                  {t('noTasksInGroup')}
                </div>
              </div>
            </div>
          )}
        </div>
      );
    },
    [virtuosoGroups, collapsedGroups, handleGroupCollapse, visibleColumns, t]
  );

  const renderTask = useCallback(
    (taskIndex: number) => {
      const item = virtuosoItems[taskIndex];

      
      if (!item || !urlProjectId) return null;
      
      if ('isAddTaskRow' in item && item.isAddTaskRow) {
        return (
          <AddTaskRow
            groupId={item.groupId}
            groupType={item.groupType}
            groupValue={item.groupValue}
            projectId={urlProjectId}
            visibleColumns={visibleColumns}
            onTaskAdded={handleTaskAdded}
          />
        );
      }
      
      return (
        <TaskRowWithSubtasks
          taskId={item.id}
          projectId={urlProjectId}
          visibleColumns={visibleColumns}
          updateTaskCustomColumnValue={updateTaskCustomColumnValue}
        />
      );
    },
    [virtuosoItems, visibleColumns, urlProjectId, handleTaskAdded, updateTaskCustomColumnValue]
  );

  // Render column headers
  const renderColumnHeaders = useCallback(() => (
    <div className="bg-gray-50 dark:bg-gray-800 border-b border-gray-200 dark:border-gray-700" style={{ width: '100%', minWidth: 'max-content' }}>
      <div className="flex items-center px-3 py-3 w-full" style={{ minWidth: 'max-content', height: '44px' }}>
        {visibleColumns.map((column, index) => {
          const columnStyle: ColumnStyle = {
            width: column.width,
            flexShrink: 0,
            ...(column.id === 'labels' && column.width === 'auto'
              ? {
                  minWidth: '200px',
                  flexGrow: 1,
                }
              : {}),
            ...((column as any).minWidth && { minWidth: (column as any).minWidth }),
            ...((column as any).maxWidth && { maxWidth: (column as any).maxWidth }),
          };

          return (
            <div
              key={column.id}
              className={`text-sm font-semibold text-gray-600 dark:text-gray-300 ${
                column.id === 'taskKey' ? 'pl-3' : ''
              }`}
              style={columnStyle}
            >
              {column.id === 'dragHandle' || column.id === 'checkbox' ? (
                <span></span>
              ) : (column as any).isCustom ? (
                <CustomColumnHeader
                  column={column}
                  onSettingsClick={handleCustomColumnSettings}
                />
              ) : (
                t(column.label || '')
              )}
            </div>
          );
        })}
        {/* Add Custom Column Button - positioned at the end and scrolls with content */}
        <div className="flex items-center justify-center ml-2" style={{ width: '50px', flexShrink: 0 }}>
          <AddCustomColumnButton />
        </div>
      </div>
    </div>
  ), [visibleColumns, t, handleCustomColumnSettings]);



  // Loading and error states
  if (loading || loadingColumns) return <Skeleton active />;
  if (error) return <div>{t('emptyStates.errorPrefix')} {error}</div>;
  
  // Show message when no data
  if (groups.length === 0 && !loading) {
    return (
      <div className="flex flex-col bg-white dark:bg-gray-900 h-full">
        <div className="flex-none" style={{ height: '74px', flexShrink: 0 }}>
          <ImprovedTaskFilters position="list" />
        </div>
        <div className="flex-1 flex items-center justify-center">
          <div className="text-center">
            <div className="text-lg font-medium text-gray-900 dark:text-white mb-2">
              {t('emptyStates.noTaskGroups')}
            </div>
            <div className="text-sm text-gray-500 dark:text-gray-400">
              {t('emptyStates.noTaskGroupsDescription')}
            </div>
          </div>
        </div>
      </div>
    );
  }

  return (
    <DndContext
      sensors={sensors}
      collisionDetection={closestCenter}
      onDragStart={handleDragStart}
      onDragOver={handleDragOver}
      onDragEnd={handleDragEnd}
    >
      <div className="flex flex-col bg-white dark:bg-gray-900 h-full overflow-hidden">
        {/* Task Filters */}
        <div className="flex-none" style={{ height: '74px', flexShrink: 0 }}>
          <ImprovedTaskFilters position="list" />
        </div>

        {/* Table Container */}
        <div 
          className="border border-gray-200 dark:border-gray-700 rounded-lg" 
          style={{ 
            height: 'calc(100vh - 130px)',
            display: 'flex',
            flexDirection: 'column',
            overflow: 'hidden'
          }}
        >
          {/* Task List Content with Sticky Header */}
          <div 
            ref={contentScrollRef}
            className="flex-1 bg-white dark:bg-gray-900 relative" 
            style={{ 
              overflowX: 'auto', 
              overflowY: 'auto', 
              minHeight: 0,
              paddingBottom: '20px' // Add padding to ensure horizontal scrollbar is visible
            }}
          >
            {/* Sticky Column Headers */}
            <div className="sticky top-0 z-30 bg-gray-50 dark:bg-gray-800" style={{ width: '100%', minWidth: 'max-content' }}>
              {renderColumnHeaders()}
            </div>
            <SortableContext
              items={virtuosoItems
                .filter(item => !('isAddTaskRow' in item) && !item.parent_task_id)
                .map(item => item.id)
                .filter((id): id is string => id !== undefined)}
              strategy={verticalListSortingStrategy}
            >
              <div style={{ minWidth: 'max-content' }}>
                {/* Render groups manually for debugging */}
                {virtuosoGroups.map((group, groupIndex) => (
                  <div key={group.id}>
                    {/* Group Header */}
                    {renderGroup(groupIndex)}
                    
                    {/* Group Tasks */}
                    {!collapsedGroups.has(group.id) && group.tasks.map((task, taskIndex) => {
                      const globalTaskIndex = virtuosoGroups
                        .slice(0, groupIndex)
                        .reduce((sum, g) => sum + g.count, 0) + taskIndex;
                      
                      return (
                        <div key={task.id || `add-task-${group.id}-${taskIndex}`}>
                          {renderTask(globalTaskIndex)}
                        </div>
                      );
                    })}
                  </div>
                ))}
              </div>
            </SortableContext>
          </div>
        </div>

        {/* Drag Overlay */}
        <DragOverlay dropAnimation={null}>
          {activeId ? (
            <div className="bg-white dark:bg-gray-800 shadow-xl rounded-md border-2 border-blue-400 opacity-95">
              <div className="px-4 py-3">
                <div className="flex items-center gap-3">
                  <HolderOutlined className="text-blue-500" />
                  <div>
                    <div className="text-sm font-medium text-gray-900 dark:text-white">
                      {allTasks.find(task => task.id === activeId)?.name ||
                        allTasks.find(task => task.id === activeId)?.title ||
                        t('emptyStates.dragTaskFallback')}
                    </div>
                    <div className="text-xs text-gray-500 dark:text-gray-400">
                      {allTasks.find(task => task.id === activeId)?.task_key}
                    </div>
                  </div>
                </div>
              </div>
            </div>
          ) : null}
        </DragOverlay>

        {/* Bulk Action Bar */}
        {selectedTaskIds.length > 0 && urlProjectId && (
          <div className="fixed bottom-6 left-1/2 transform -translate-x-1/2 z-50">
            <OptimizedBulkActionBar
              selectedTaskIds={selectedTaskIds}
              totalSelected={selectedTaskIds.length}
              projectId={urlProjectId}
              onClearSelection={bulkActions.handleClearSelection}
              onBulkStatusChange={(statusId) => bulkActions.handleBulkStatusChange(statusId, selectedTaskIds)}
              onBulkPriorityChange={(priorityId) => bulkActions.handleBulkPriorityChange(priorityId, selectedTaskIds)}
              onBulkPhaseChange={(phaseId) => bulkActions.handleBulkPhaseChange(phaseId, selectedTaskIds)}
              onBulkAssignToMe={() => bulkActions.handleBulkAssignToMe(selectedTaskIds)}
              onBulkAssignMembers={(memberIds) => bulkActions.handleBulkAssignMembers(memberIds, selectedTaskIds)}
              onBulkAddLabels={(labelIds) => bulkActions.handleBulkAddLabels(labelIds, selectedTaskIds)}
              onBulkArchive={() => bulkActions.handleBulkArchive(selectedTaskIds)}
              onBulkDelete={() => bulkActions.handleBulkDelete(selectedTaskIds)}
              onBulkDuplicate={() => bulkActions.handleBulkDuplicate(selectedTaskIds)}
              onBulkExport={() => bulkActions.handleBulkExport(selectedTaskIds)}
              onBulkSetDueDate={(date) => bulkActions.handleBulkSetDueDate(date, selectedTaskIds)}
            />
          </div>
        )}

        {/* Custom Column Modal */}
        {createPortal(<CustomColumnModal />, document.body, 'custom-column-modal')}
      </div>
    </DndContext>
  );
};

export default TaskListV2;
