(function(){
  // 全局图像缓存对象 存放已加载的图像资源
  window.YooneSnowImageCache = window.YooneSnowImageCache || {};

  // 获取或加载图像 根据 URL 返回图像对象和加载状态
  window.YooneSnowGetOrLoadImage = function(imageUrl){
    // 条件判断 如果未提供 URL 则返回空
    if (!imageUrl || typeof imageUrl !== 'string'){
      return { img: null, ready: false };
    }
    const existing = window.YooneSnowImageCache[imageUrl];
    // 条件判断 如果已存在缓存则直接返回
    if (existing && existing.ready){
      return existing;
    }
    if (existing && !existing.ready){
      // 条件判断 如果正在加载则返回当前状态
      return existing;
    }
    // 创建新的图像对象 并开始加载
    const img = new Image();
    const record = { img: img, ready: false };
    window.YooneSnowImageCache[imageUrl] = record;
    try { img.decoding = 'async'; } catch(e) {}
    try { img.fetchPriority = 'low'; } catch(e) {}
    img.onload = function(){ record.ready = true; };
    img.onerror = function(){
      // 加载失败 从缓存移除避免重复错误
      delete window.YooneSnowImageCache[imageUrl];
    };
    img.src = imageUrl;
    return record;
  };

  window.YooneSnowLoadAssetViaFetch = function(imageUrl, onReady){
    if (!imageUrl || typeof imageUrl !== 'string'){
      if (typeof onReady === 'function'){ onReady(false); }
      return;
    }
    var existing = window.YooneSnowImageCache[imageUrl];
    if (existing && existing.ready){
      if (typeof onReady === 'function'){ onReady(true); }
      return;
    }
    if (!existing){ window.YooneSnowImageCache[imageUrl] = { img: null, ready: false }; }
    if (typeof fetch === 'function' && typeof createImageBitmap === 'function'){
      fetch(imageUrl, { cache: 'force-cache' }).then(function(resp){ return resp.blob(); }).then(function(blob){
        return createImageBitmap(blob);
      }).then(function(bmp){
        window.YooneSnowImageCache[imageUrl] = { img: bmp, ready: true };
        if (typeof onReady === 'function'){ onReady(true); }
      }).catch(function(){
        var rec = window.YooneSnowGetOrLoadImage(imageUrl);
        var fired = false;
        if (rec && rec.img){
          var markReady = function(){ rec.ready = true; };
          rec.img.onload = function(){ if (!fired){ fired = true; markReady(); if (typeof onReady === 'function'){ onReady(true); } } };
          rec.img.onerror = function(){ if (!fired){ fired = true; if (typeof onReady === 'function'){ onReady(false); } } };
        }
      });
    } else {
      var rec2 = window.YooneSnowGetOrLoadImage(imageUrl);
      var fired2 = false;
      if (rec2 && rec2.img){
        var markReady2 = function(){ rec2.ready = true; };
        rec2.img.onload = function(){ if (!fired2){ fired2 = true; markReady2(); if (typeof onReady === 'function'){ onReady(true); } } };
        rec2.img.onerror = function(){ if (!fired2){ fired2 = true; if (typeof onReady === 'function'){ onReady(false); } } };
      }
    }
  };

  // 居中绘制图像 根据目标中心点和宽高进行缩放绘制
  window.YooneSnowDrawCenteredImage = function(context, img, centerX, centerY, width, height){
    // 条件判断 如果图像不存在则不绘制
    if (!img) { return; }
    const drawX = centerX - width / 2;
    const drawY = centerY - height / 2;
    context.drawImage(img, drawX, drawY, width, height);
  };
})();