/**
 * 图片处理工具函数
 * 用于压缩和切片图片
 */

/**
 * 加载图片文件为HTMLImageElement
 */
export function loadImage(file: File): Promise<HTMLImageElement> {
  return new Promise((resolve, reject) => {
    if (typeof window === 'undefined') {
      reject(new Error('仅在浏览器环境中支持图片处理'))
      return
    }
    const img = window.document.createElement('img')
    img.onload = () => {
      URL.revokeObjectURL(img.src)
      resolve(img)
    }
    img.onerror = (err) => {
      URL.revokeObjectURL(img.src)
      reject(err)
    }
    img.src = URL.createObjectURL(file)
  })
}

/**
 * 将Canvas转换为File
 */
export function canvasToFile(
  canvas: HTMLCanvasElement,
  origin: File,
  quality = 0.85,
  suffix = ''
): Promise<File> {
  return new Promise((resolve, reject) => {
    canvas.toBlob(
      (blob) => {
        if (!blob) {
          reject(new Error('图片压缩失败'))
          return
        }
        const baseName = origin.name.replace(/\.[^/.]+$/, '')
        const ext = '.jpg'
        const fileName = suffix ? `${baseName}${suffix}${ext}` : `${baseName}${ext}`
        resolve(new File([blob], fileName, { type: 'image/jpeg' }))
      },
      'image/jpeg',
      quality
    )
  })
}

/**
 * 预览图：只做压缩，不切片
 */
export async function compressPreviewImage(file: File): Promise<File> {
  const img = await loadImage(file)
  const maxWidth = 800
  const maxHeight = 2000
  let { width, height } = img
  const ratio = Math.min(maxWidth / width, maxHeight / height, 1)
  const canvas = document.createElement('canvas')
  canvas.width = Math.round(width * ratio)
  canvas.height = Math.round(height * ratio)
  const ctx = canvas.getContext('2d')
  if (!ctx) throw new Error('无法获取画布上下文')
  ctx.drawImage(img, 0, 0, canvas.width, canvas.height)
  return await canvasToFile(canvas, file, 0.85)
}

/**
 * 展示图：压缩 + 切片，高度>1500则按 1500px 一段切
 */
export async function compressAndSliceDisplayImage(file: File): Promise<File[]> {
  const img = await loadImage(file)
  const maxWidth = 800
  const maxHeight = 2000
  let { width, height } = img
  const ratio = Math.min(maxWidth / width, maxHeight / height, 1)
  const targetWidth = Math.round(width * ratio)
  const targetHeight = Math.round(height * ratio)
  const sliceMaxHeight = 1500

  const results: File[] = []

  if (targetHeight <= sliceMaxHeight) {
    const canvas = document.createElement('canvas')
    canvas.width = targetWidth
    canvas.height = targetHeight
    const ctx = canvas.getContext('2d')
    if (!ctx) throw new Error('无法获取画布上下文')
    ctx.drawImage(img, 0, 0, targetWidth, targetHeight)
    const f = await canvasToFile(canvas, file, 0.85)
    results.push(f)
    return results
  }

  // 需要切片
  const sliceCount = Math.ceil(targetHeight / sliceMaxHeight)
  for (let i = 0; i < sliceCount; i++) {
    const sliceTop = i * sliceMaxHeight
    const sliceHeight = Math.min(sliceMaxHeight, targetHeight - sliceTop)
    const canvas = document.createElement('canvas')
    canvas.width = targetWidth
    canvas.height = sliceHeight
    const ctx = canvas.getContext('2d')
    if (!ctx) throw new Error('无法获取画布上下文')
    ctx.drawImage(
      img,
      0,
      sliceTop / ratio,
      width,
      sliceHeight / ratio,
      0,
      0,
      targetWidth,
      sliceHeight
    )
    const f = await canvasToFile(canvas, file, 0.85, `-part${i + 1}`)
    results.push(f)
  }
  return results
}