import { probeImageTransparency } from './imageTransparency'

const IMAGE_UPLOAD_MAX_SIDE: Record<string, number> = {
  avatar: 512,
  chat: 1280,
  announcement: 1600,
  'home-banner': 1920,
  'aw-recycle': 1920,
  'cooperation-feedback': 1920,
  listing: 1920,
  dispute: 1920,
  handoff: 1920,
  realname: 1920,
  qrcode: 2560,
}

const IMAGE_UPLOAD_QUALITY: Record<string, number> = {
  avatar: 0.82,
  chat: 0.8,
  announcement: 0.84,
  'home-banner': 0.84,
  'aw-recycle': 0.84,
  'cooperation-feedback': 0.84,
  listing: 0.84,
  dispute: 0.86,
  handoff: 0.86,
  realname: 0.86,
  qrcode: 0.95,
}

export interface UploadEncoding {
  maxSide: number
  quality: number
  outputType: 'image/webp' | 'image/png'
  extension: 'webp' | 'png'
}

/**
 * 决定上传前的压缩参数。
 *
 * 关键点：带透明通道的图（例如热区透明按钮图、透明 Logo）必须输出 PNG，
 * 否则压缩过程会把透明区域压成实色（历史上就是先铺白底再编码，导致透明按钮图变白底方块）。
 */
export function resolveUploadEncoding(scene: string, preserveAlpha: boolean): UploadEncoding {
  const maxSide = IMAGE_UPLOAD_MAX_SIDE[scene] ?? 1600
  const quality = IMAGE_UPLOAD_QUALITY[scene] ?? 0.82
  return {
    maxSide,
    quality,
    outputType: preserveAlpha ? 'image/png' : 'image/webp',
    extension: preserveAlpha ? 'png' : 'webp',
  }
}

export async function optimizeImageForUpload(file: File, scene: string) {
  if (!file.type.startsWith('image/')) return file
  if (!['image/jpeg', 'image/png', 'image/webp'].includes(file.type)) return file
  if (typeof document === 'undefined') return file

  try {
    // 先判断原图是否真的有透明像素：有则全程保留 alpha
    const probe = await probeImageTransparency(file)
    const preserveAlpha = Boolean(probe?.hasTransparentPixels)
    const { maxSide, quality, outputType, extension } = resolveUploadEncoding(scene, preserveAlpha)

    const image = await loadImage(file)
    const { width, height } = fitSize(image.naturalWidth, image.naturalHeight, maxSide)
    const canvas = document.createElement('canvas')
    canvas.width = width
    canvas.height = height
    const context = canvas.getContext('2d')
    if (!context) return file
    // 不铺白底：canvas 本身保留透明，输出 PNG / WebP 都能带 alpha
    context.clearRect(0, 0, width, height)
    context.drawImage(image, 0, 0, width, height)
    const blob = await canvasToBlob(canvas, outputType, quality)
    if (!blob || blob.size >= file.size) return file
    return new File([blob], replaceFileExt(file.name, extension), {
      type: outputType,
      lastModified: Date.now(),
    })
  } catch {
    return file
  }
}

function loadImage(file: File) {
  return new Promise<HTMLImageElement>((resolve, reject) => {
    const url = URL.createObjectURL(file)
    const image = new Image()
    image.onload = () => {
      URL.revokeObjectURL(url)
      resolve(image)
    }
    image.onerror = () => {
      URL.revokeObjectURL(url)
      reject(new Error('图片读取失败'))
    }
    image.src = url
  })
}

function fitSize(width: number, height: number, maxSide: number) {
  if (width <= 0 || height <= 0) return { width: 1, height: 1 }
  const scale = Math.min(1, maxSide / Math.max(width, height))
  return {
    width: Math.max(1, Math.round(width * scale)),
    height: Math.max(1, Math.round(height * scale)),
  }
}

function canvasToBlob(canvas: HTMLCanvasElement, type: string, quality: number) {
  return new Promise<Blob | null>(resolve => {
    canvas.toBlob(resolve, type, quality)
  })
}

function replaceFileExt(filename: string, ext: string) {
  const base = filename.replace(/\.[^.]+$/, '')
  return `${base || 'image'}.${ext}`
}