import type React from 'react'

const FALLBACK_IMAGE_EXTENSIONS = new Set([
  'avif',
  'bmp',
  'gif',
  'jpeg',
  'jpg',
  'png',
  'webp',
])

export interface ImageFileValidationOptions {
  maxBytes?: number
  maxCount?: number
  existingCount?: number
  /**
   * 可选的业务格式白名单。浏览器的 image/* MIME 范围比实际处理能力更宽，
   * 需要在特定上传链路中按扩展名提前拦截不兼容格式。
   */
  allowedExtensions?: readonly string[]
}

export interface ImageFileValidationResult {
  acceptedFiles: File[]
  errors: string[]
}

export function hasDragLeftDropZone(event: React.DragEvent<Element>): boolean {
  const nextTarget = event.relatedTarget as Node | null
  if (nextTarget && nextTarget !== event.currentTarget) {
    return !event.currentTarget.contains(nextTarget)
  }

  const rect = event.currentTarget.getBoundingClientRect()
  const { clientX, clientY } = event
  return clientX <= rect.left || clientX >= rect.right || clientY <= rect.top || clientY >= rect.bottom
}

export function prepareFileDrag(event: React.DragEvent<Element>, disabled = false): void {
  event.preventDefault()
  event.stopPropagation()
  event.dataTransfer.dropEffect = disabled ? 'none' : 'copy'
}

/**
 * 让拖拽上传区域也能通过键盘打开文件选择器，避免只能用鼠标点击。
 */
export function handleDropZoneKeyDown(
  event: React.KeyboardEvent<HTMLElement>,
  openFilePicker: () => void,
): void {
  if (event.target !== event.currentTarget) return
  if (event.key !== 'Enter' && event.key !== ' ') return
  event.preventDefault()
  openFilePicker()
}

export function isSupportedImageFile(file: File): boolean {
  if (file.type) {
    return file.type.startsWith('image/')
  }

  const extension = getFileExtension(file)
  return FALLBACK_IMAGE_EXTENSIONS.has(extension)
}

export function getFileExtension(file: File): string {
  return file.name.split('.').pop()?.toLowerCase() || ''
}

export function hasAllowedFileExtension(file: File, allowedExtensions: readonly string[]): boolean {
  const extension = getFileExtension(file)
  return allowedExtensions.some((allowedExtension) => allowedExtension.replace(/^\./, '').toLowerCase() === extension)
}

export function validateImageFiles(
  files: FileList | File[],
  options: ImageFileValidationOptions = {},
): ImageFileValidationResult {
  const { maxBytes, maxCount, existingCount = 0, allowedExtensions } = options
  const unsupportedNames: string[] = []
  const oversizedNames: string[] = []
  const validFiles: File[] = []

  for (const file of Array.from(files)) {
    const isValidImage = allowedExtensions
      ? hasAllowedFileExtension(file, allowedExtensions)
      : isSupportedImageFile(file)
    if (!isValidImage) {
      unsupportedNames.push(file.name)
      continue
    }

    if (maxBytes !== undefined && file.size > maxBytes) {
      oversizedNames.push(file.name)
      continue
    }

    validFiles.push(file)
  }

  const remainingCount = maxCount === undefined
    ? validFiles.length
    : Math.max(0, maxCount - existingCount)
  const acceptedFiles = validFiles.slice(0, remainingCount)
  const ignoredByCount = Math.max(0, validFiles.length - acceptedFiles.length)
  const errors: string[] = []

  if (unsupportedNames.length > 0) {
    const supportedLabel = allowedExtensions?.length
      ? `，请上传 ${allowedExtensions.map((extension) => extension.replace(/^\./, '').toUpperCase()).join('、')} 格式`
      : ''
    errors.push(`以下文件不是支持的图片格式：${unsupportedNames.join('、')}${supportedLabel}`)
  }
  if (oversizedNames.length > 0 && maxBytes !== undefined) {
    const maxMegabytes = Math.round(maxBytes / 1024 / 1024)
    errors.push(`以下图片超过 ${maxMegabytes}MB：${oversizedNames.join('、')}`)
  }
  if (ignoredByCount > 0 && maxCount !== undefined) {
    errors.push(`最多只能选择 ${maxCount} 张图片，已忽略 ${ignoredByCount} 张`)
  }

  return { acceptedFiles, errors }
}