import { ElMessage } from 'element-plus';

export interface CompressionLevel {
  maxWidth: number;
  maxHeight: number;
  quality: number;
}

export const DEFAULT_COMPRESSION_LEVELS: CompressionLevel[] = [
  { maxWidth: 800, maxHeight: 800, quality: 0.6 },
  { maxWidth: 600, maxHeight: 600, quality: 0.5 },
  { maxWidth: 400, maxHeight: 400, quality: 0.4 },
];

/**
 * 压缩图片
 * @param file - 要压缩的图片文件
 * @param maxWidth - 最大宽度
 * @param maxHeight - 最大高度
 * @param quality - 压缩质量 (0-1)
 * @returns 压缩后的 Blob
 */
export function compressImage(
  file: File,
  maxWidth = 1024,
  maxHeight = 1024,
  quality = 0.8,
): Promise<Blob> {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = (e) => {
      const img = new Image();
      img.onload = () => {
        const canvas = document.createElement('canvas');
        let width = img.width;
        let height = img.height;

        if (width > maxWidth || height > maxHeight) {
          const ratio = Math.min(maxWidth / width, maxHeight / height);
          width = width * ratio;
          height = height * ratio;
        }

        canvas.width = width;
        canvas.height = height;

        const ctx = canvas.getContext('2d')!;
        ctx.drawImage(img, 0, 0, width, height);

        canvas.toBlob(
          (blob) => {
            if (blob) {
              resolve(blob);
            }
            else {
              reject(new Error('压缩失败'));
            }
          },
          file.type,
          quality,
        );
      };
      img.onerror = reject;
      img.src = e.target?.result as string;
    };
    reader.onerror = reject;
    reader.readAsDataURL(file);
  });
}

/**
 * 将 Blob 转换为 base64
 * @param blob - Blob 对象
 * @returns base64 字符串
 */
export function blobToBase64(blob: Blob): Promise<string> {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onload = () => {
      resolve(reader.result as string);
    };
    reader.onerror = reject;
    reader.readAsDataURL(blob);
  });
}

/**
 * 尝试多级压缩直到满足大小限制
 * @param file - 图片文件
 * @param currentTotalLength - 当前已使用的总长度
 * @param maxTotalLength - 最大允许总长度
 * @returns 压缩结果或 null（如果无法满足限制）
 */
export async function tryCompressToLimit(
  file: File,
  currentTotalLength: number,
  maxTotalLength: number,
  compressionLevels = DEFAULT_COMPRESSION_LEVELS,
): Promise<{ blob: Blob; base64: string; estimatedLength: number } | null> {
  for (const level of compressionLevels) {
    const compressedBlob = await compressImage(
      file,
      level.maxWidth,
      level.maxHeight,
      level.quality,
    );
    const base64 = await blobToBase64(compressedBlob);
    const estimatedLength = Math.floor(base64.length * 0.5);

    if (currentTotalLength + estimatedLength <= maxTotalLength) {
      return { blob: compressedBlob, base64, estimatedLength };
    }
  }
  return null;
}

/**
 * Composable: 使用图片压缩
 */
export function useImageCompression() {
  return {
    compressImage,
    blobToBase64,
    tryCompressToLimit,
    DEFAULT_COMPRESSION_LEVELS,
  };
}