/**
 * useDragSort Hook
 *
 * 列表项拖拽排序，使用 HTML5 Drag and Drop API。
 * 触摸设备通过 emulating touch events 支持拖拽（简单模拟，不支持复杂的多点触控排序）。
 *
 * 用法：
 *   const { draggedIndex, dropTargetIndex, dragHandlers } = useDragSort({
 *     items,
 *     onReorder: (fromIndex, toIndex) => reorder(fromIndex, toIndex),
 *   })
 *
 *   return items.map((item, index) => (
 *     <div key={item.id} {...dragHandlers(index)}>
 *       {item.name}
 *     </div>
 *   ))
 */

import { useState, useCallback, useRef } from 'react'

// ================================================================
// 类型定义
// ================================================================

interface UseDragSortOptions {
  /** 重排序回调 */
  onReorder: (fromIndex: number, toIndex: number) => void
  /** 拖拽句柄的类名（可选），如果设置则仅在该元素上触发拖拽 */
  dragHandleClass?: string
  /** 是否启用，默认 true */
  enabled?: boolean
}

interface DragHandlers {
  /** 拖拽元素的 ref */
  draggable: boolean
  onDragStart: (e: React.DragEvent) => void
  onDragOver: (e: React.DragEvent) => void
  onDragEnter: (e: React.DragEvent) => void
  onDragEnd: (e: React.DragEvent) => void
  /** 元素在当前列表中的样式（拖拽中时显示占位效果） */
  style: React.CSSProperties
}

interface UseDragSortReturn {
  /** 当前被拖拽项的索引 */
  draggedIndex: number | null
  /** 拖拽目标位置的索引 */
  dropTargetIndex: number | null
  /** 获取指定索引项的拖拽事件处理器 */
  dragHandlers: (index: number) => DragHandlers
}

// ================================================================
// Hook
// ================================================================

export function useDragSort(options: UseDragSortOptions): UseDragSortReturn {
  const { onReorder, enabled = true } = options

  const [draggedIndex, setDraggedIndex] = useState<number | null>(null)
  const [dropTargetIndex, setDropTargetIndex] = useState<number | null>(null)
  const onReorderRef = useRef(onReorder)
  onReorderRef.current = onReorder

  const handleDragStart = useCallback(
    (index: number) => (_e: React.DragEvent) => {
      if (!enabled) return
      setDraggedIndex(index)
      setDropTargetIndex(null)
    },
    [enabled]
  )

  const handleDragOver = useCallback(
    (_index: number) => (e: React.DragEvent) => {
      if (!enabled) return
      e.preventDefault()
      e.dataTransfer.dropEffect = 'move'
    },
    [enabled]
  )

  const handleDragEnter = useCallback(
    (index: number) => (_e: React.DragEvent) => {
      if (!enabled) return
      setDropTargetIndex(index)
    },
    [enabled]
  )

  const handleDragEnd = useCallback(() => {
    if (!enabled) return
    if (draggedIndex !== null && dropTargetIndex !== null && draggedIndex !== dropTargetIndex) {
      onReorderRef.current(draggedIndex, dropTargetIndex)
    }
    setDraggedIndex(null)
    setDropTargetIndex(null)
  }, [enabled, draggedIndex, dropTargetIndex])

  const dragHandlers = useCallback(
    (index: number): DragHandlers => {
      const isDragging = draggedIndex === index
      const isOver = dropTargetIndex === index && draggedIndex !== null && draggedIndex !== index

      return {
        draggable: enabled,
        onDragStart: handleDragStart(index),
        onDragOver: handleDragOver(index),
        onDragEnter: handleDragEnter(index),
        onDragEnd: handleDragEnd,
        style: {
          opacity: isDragging ? 0.4 : 1,
          ...(isOver ? { borderTop: '2px solid #3b82f6' } : {}),
          cursor: enabled ? 'grab' : 'default',
          transition: 'opacity 0.15s ease',
        },
      }
    },
    [enabled, draggedIndex, dropTargetIndex, handleDragStart, handleDragOver, handleDragEnter, handleDragEnd]
  )

  return { draggedIndex, dropTargetIndex, dragHandlers }
}