import { Injectable, type NestMiddleware } from '@nestjs/common';
import type { NextFunction, Request, Response } from 'express';
import sanitizeHtml from 'sanitize-html';

const SANITIZE_OPTIONS: sanitizeHtml.IOptions = {
  allowedTags: [],
  allowedAttributes: {},
  disallowedTagsMode: 'recursiveEscape',
};

function sanitizeValue(value: unknown): unknown {
  if (typeof value === 'string') {
    return sanitizeHtml(value, SANITIZE_OPTIONS);
  }
  if (Array.isArray(value)) {
    return value.map(sanitizeValue);
  }
  if (value !== null && typeof value === 'object') {
    return sanitizeObject(value as Record<string, unknown>);
  }
  return value;
}

function sanitizeObject(obj: Record<string, unknown>): Record<string, unknown> {
  const sanitized: Record<string, unknown> = {};
  for (const [key, val] of Object.entries(obj)) {
    sanitized[key] = sanitizeValue(val);
  }
  return sanitized;
}

/**
 * Strips HTML tags from all string values in request body, query, and params
 * to prevent stored XSS attacks.
 */
@Injectable()
export class SanitizeInputMiddleware implements NestMiddleware {
  use(req: Request, _res: Response, next: NextFunction): void {
    if (req.body && typeof req.body === 'object') {
      req.body = sanitizeObject(req.body as Record<string, unknown>);
    }
    if (req.query && typeof req.query === 'object') {
      for (const [key, val] of Object.entries(req.query)) {
        (req.query as Record<string, unknown>)[key] = sanitizeValue(val);
      }
    }
    if (req.params && typeof req.params === 'object') {
      for (const [key, val] of Object.entries(req.params)) {
        (req.params as Record<string, unknown>)[key] = sanitizeValue(val);
      }
    }
    next();
  }
}