/** OSS 单文件上限（与后端 OSS_MAX_UPLOAD_BYTES 默认一致） */
export const DEFAULT_OSS_MAX_UPLOAD_BYTES = 10 * 1024 * 1024;

function isCompressibleImage(file: File): boolean {
  if (!file.type.startsWith('image/')) return false;
  if (file.type === 'image/svg+xml' || file.type === 'image/gif') return false;
  return true;
}

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

function canvasToBlob(canvas: HTMLCanvasElement, type: string, quality: number): Promise<Blob> {
  return new Promise((resolve, reject) => {
    canvas.toBlob(
      (blob) => (blob ? resolve(blob) : reject(new Error('图片压缩失败'))),
      type,
      quality,
    );
  });
}

async function renderScaled(
  img: HTMLImageElement,
  maxEdge: number,
  quality: number,
  mime: string,
): Promise<Blob> {
  const w = img.naturalWidth;
  const h = img.naturalHeight;
  const scale = Math.min(1, maxEdge / Math.max(w, h));
  const cw = Math.max(1, Math.round(w * scale));
  const ch = Math.max(1, Math.round(h * scale));
  const canvas = document.createElement('canvas');
  canvas.width = cw;
  canvas.height = ch;
  const ctx = canvas.getContext('2d');
  if (!ctx) throw new Error('图片压缩失败');
  ctx.drawImage(img, 0, 0, cw, ch);
  return canvasToBlob(canvas, mime, quality);
}

/**
 * 超过 maxBytes 的图片用 canvas 压缩后再上传；不可压缩或非图片原样返回。
 */
export async function compressImageFileIfNeeded(
  file: File,
  maxBytes = DEFAULT_OSS_MAX_UPLOAD_BYTES,
): Promise<File> {
  if (!isCompressibleImage(file) || file.size <= maxBytes) return file;

  const img = await loadImage(file);
  const mime = file.type === 'image/png' || file.type === 'image/webp' ? 'image/jpeg' : file.type || 'image/jpeg';
  const edges = [4096, 3072, 2048, 1536, 1280, 1024, 800];
  let best: Blob | null = null;

  outer: for (const edge of edges) {
    for (let quality = 0.92; quality >= 0.5; quality -= 0.08) {
      const blob = await renderScaled(img, edge, quality, mime);
      if (!best || blob.size < best.size) best = blob;
      if (blob.size <= maxBytes) {
        best = blob;
        break outer;
      }
    }
  }

  if (!best || best.size >= file.size) return file;

  const ext = mime === 'image/png' ? '.png' : '.jpg';
  const baseName = file.name.replace(/\.[^.]+$/, '') || 'image';
  return new File([best], `${baseName}${ext}`, { type: mime, lastModified: Date.now() });
}

export function formatOssMaxSizeMb(maxBytes = DEFAULT_OSS_MAX_UPLOAD_BYTES): number {
  return Math.floor(maxBytes / 1024 / 1024);
}