middleware.js

 const Listing=require("./models/listing.js");
 const Review=require("./models/review.js");
const ExpressError=require("./utils/ExpressError.js");
const {listingSchema,reviewSchema}=require("./schema.js");
// isLogged in middleware
 module.exports.isLoggedIn=(req,res,next)=>{
     if(!req.isAuthenticated()){
      req.session.redirectUrl=req.originalUrl;// saving url data that the user was tring to reach
     req.flash("error","You must be Logged in !!");
     return res.redirect("/login");
   }
   next();
 }
 //saving req.session.redirectUrl in locals--

 module.exports.saveRedirectUrl=(req,res,next)=>{
  if(req.session.redirectUrl){
    res.locals.redirectUrl=req.session.redirectUrl;
  }
  next();
 }
//Iowner middleware---
 module.exports.isOwner= async (req,res,next)=>{
  let {id}=req.params;
 let listing= await Listing.findById(id);
 if (!listing.owner._id.equals(res.locals.currUser._id)){
  req.flash("error","You are not the Owner!!");
  return res.redirect(`/listings/${id}`)
 }
 next();
 }

 //validateListing middleware---
 module.exports.validateListing=(req,res,next)=>{
      
  let {error}=listingSchema.validate(req.body);
  
  if(error){
   let errMsg=error.details.map((el)=>el.message).join(",");
   throw new ExpressError(400,error)
  }else{
   next();
  }
 }

 //validateReview middleware---
 module.exports.validateReview=(req,res,next)=>{
     
 let {error}=reviewSchema.validate(req.body);
 
 if(error){
  let errMsg=error.details.map((el)=>el.message).join(",");
  throw new ExpressError(400,errMsg)
 }else{
  next();
 }
}
//isReviewAuthor middleware---
 module.exports.isReviewAuthor= async (req,res,next)=>{
  let {id,reviewId}=req.params;
 let review= await Review.findById(reviewId);
 if (!review.author._id.equals(res.locals.currUser._id)){
  req.flash("error","You are not the Author of this review!");
  return res.redirect(`/listings/${id}`)
 }
 next();
 }