import {
  Injectable,
  NestMiddleware,
  BadRequestException,
} from '@nestjs/common';
import { Request, Response, NextFunction } from 'express';
import multer, { Multer } from 'multer';
import path from 'path';
import fs from 'fs';

const ALLOWED_MIME = ['image/jpeg', 'image/png', 'image/webp'];
const MAX_SIZE = 2 * 1024 * 1024; // 2M

/**
 * 文件上传中间件（按日期分文件夹）
 * 单图字段名固定：file
 */
@Injectable()
export class UploadMiddleware implements NestMiddleware {
  private readonly upload: Multer;

  constructor() {
    const root = process.env.UPLOAD_ROOT ?? './uploads';
    this.upload = multer({
      storage: multer.diskStorage({
        destination: (_req, _file, cb) => {
          const date = new Date();
          const dir = path.join(
            process.cwd(),
            root.replace(/^\.\/?/, ''),
            `${date.getFullYear()}/${String(date.getMonth() + 1).padStart(2, '0')}`,
          );
          fs.mkdirSync(dir, { recursive: true });
          cb(null, dir);
        },
        filename: (_req, file, cb) => {
          const ext = path.extname(file.originalname).toLowerCase();
          const name = `${Date.now()}_${Math.random().toString(36).slice(2, 8)}${ext}`;
          cb(null, name);
        },
      }),
      fileFilter: (_req, file, cb) => {
        if (ALLOWED_MIME.includes(file.mimetype)) {
          cb(null, true);
        } else {
          // FileFilterCallback 重载：错误时只传 Error，不传 acceptFile
          cb(new Error('仅支持 jpg/png/jpeg/webp 格式图片'));
        }
      },
      limits: { fileSize: MAX_SIZE },
    });
  }

  use(req: Request, _res: Response, next: NextFunction): void {
    // @types/express 与 @types/multer 内嵌的 @types/express-serve-static-core 版本不一致，
    // 运行时完全等价，这里用一次类型断言绕过编译期差异
    const single = this.upload.single('file') as (
      req: Request,
      res: Response,
      cb: (err: unknown) => void,
    ) => void;
    single(req, _res, (err) => {
      if (err) {
        next(new BadRequestException(err.message ?? '文件上传失败'));
        return;
      }
      next();
    });
  }
}