function createValidation<T>(
  schema: Schema<object> | ObjectSchemaDefinition<object>,
  entityFrom: 'query' | 'body' | 'request' = 'body',
  options?: ExpressYupMiddlewareOptions,
): QueryValidator<T> | BodyValidator<T> | RequestValidator;

import createValidation from 'express-yup-middleware';
import express from 'express';
import * as Yup from 'yup';

const validate = createValidation({
  name: Yup.string('Name must be a string!')
    .min(3, 'Name too short!')
    .required('Name is required!'),
});

const app = express();

app.post('/save-name', [
  validate,
  (req, res) => {
    /* req.body.name has been validated! */
  },
]);

/* here req.body must be an object */
createValidation({
  name: Yup.string().required(),
});

// or
/* here req.body must also be an object */
createValidation(
  Yup.object().shape({
    name: Yup.string().required(),
  }),
);

// or
/* here req.body must be an array */
createValidation(Yup.array());

/* here req.body must be an object */
createValidation(
  {
    name: Yup.string().required(),
  },
  'body',
);

// or
/* here req.body must also be an object */
createValidation(
  Yup.object().shape({
    name: Yup.string().required(),
  }),
  'query',
);

// or
/* here req.body must be an array */
createValidation(Yup.string(), 'request', {
  entityPath: ['headers', 'authroization'],
});

type ExpressYupMiddlewareOptions = {
  // Yup schema.validate(options) object. Check their documentation! (link below)
  /* Defaults are:
   * {
   *   strict: true,
   *   stripUnknown: true,
   *   abortEarly: false,
   * }
   */
  validateOptions?: ValidateOptions;

  // Whenever validation fails, how to send the response to client?
  responseOptions?: {
    // res.status(errorCode), defaults is 422 (Unprocessable Entity)
    errorCode?: number;
    // should we return errors to the client? default is true
    returnErrors?: boolean;

    // If you need to transform errors returned from Yup before sending them:
    transformErrors?: (errors: Array<string>) => any;
  };

  // where in the given object is the data to be validated (uses lodash.get to access data)
  // if you want to only validate nested data (eg: req.body.data), pass 'data'
  // if 'entityFrom' is 'request' and you want to access, for example, req.files, pass 'files';
  entityPath?: string | number | Array<string | number>;

  // If you need to transform the entity in some way before validating:
  transformEntity?: (entity: any) => any;
};

const app = express();

const validateHeader = createValidation(
  Yup.string().required('Authorization'),
  'request',
  { entityPath: ['headers', 'Authorization'] },
);

app.use(validateHeader);

const validateLogin = createValidation(
  {
    email: Yup.string().email().required(),
    password: Yup.string().required(),
  },
  'body',
  { responseOptions: { errorCode: 401 } },
);

app.post('/login', [
  validateLogin,
  (req, res) => {
    /* do login */
  },
]);