import { useMemo } from 'react'

type UsePlaceholderRowsOptions<TData> = {
  /** Actual data to display when loaded */
  data: TData[]
  /** Loading state */
  isLoading: boolean
  /** Page size for dynamic placeholder count (from pagination) */
  pageSize?: number
  /** Custom placeholder count - if provided, overrides all other placeholder count logic */
  placeholderCount?: number
}

type UsePlaceholderRowsResult<TData> = {
  /** Data array - either actual data or placeholder array of nulls */
  data: TData[] | null[]
  /** Loading state */
  isLoading: boolean
}

/**
 * Hook that generates placeholder rows for DataTable loading states.
 *
 * Placeholder count priority when loading:
 * 1. `placeholderCount` - if provided, always uses this value (overrides everything)
 * 2. If `data` has items - uses `data.length`
 * 3. If `pageSize` is provided (from pagination) - uses `pageSize`
 * 4. Default: 5
 *
 * @example
 * ```tsx
 * const tableData = usePlaceholderRows({
 *   data: myData,
 *   isLoading: isLoading,
 *   pageSize: 10,
 * })
 *
 * <DataTable
 *   data={tableData.data}
 *   isLoading={tableData.isLoading}
 * />
 * ```
 */
export function usePlaceholderRows<TData>(
  options: UsePlaceholderRowsOptions<TData>,
): UsePlaceholderRowsResult<TData> {
  const { data, isLoading, pageSize, placeholderCount } = options

  const result = useMemo(() => {
    // If loading, return placeholder array
    if (isLoading) {
      // Priority: placeholderCount > data.length > pageSize > default (5)
      let count: number
      if (placeholderCount !== undefined) {
        // 1. placeholderCount overrides everything
        count = placeholderCount
      } else if (data.length > 0) {
        // 2. If data has items, use its length
        count = data.length
      } else if (pageSize !== undefined) {
        // 3. If pagination is provided, use pageSize
        count = pageSize
      } else {
        // 4. Default to 5
        count = 5
      }

      return {
        data: new Array(count).fill(null) as null[],
        isLoading: true,
      }
    }

    // If not loading, return actual data
    return {
      data,
      isLoading: false,
    }
  }, [data, isLoading, pageSize, placeholderCount])

  return result
}