Mongo DB errors. Please help. Thank you.

const express $=$ require$(\text{'}$express$\text{'})$;

const cors $=$ require$(\text{'}$cors$\text{'})$;

const multer $=$ require$(\text{'}$multer$\text{'})$;

const Joi $=$ require$(\text{'}$joi$\text{'})$;

const mongoose $=$ require$(\text{'}$mongoose$\text{'})$;

const app $=$ express$()$;

$//$ Middleware Setup

app.use$($cors$())$;

app.use$($express$.$json$())$;

app.use$($express$.$static$(\text{'}$public$\text{'}))$;

$//$ Multer Storage Configuration

const storage $=$ multer.diskStorage$(\{$

destination: $($req$,$ file, cb$)=>\{$

cb$($null$,\text{'}./$public$/$images$\text{'})$; $//$ Ensure the directory exists

$\},$

filename: $($req$,$ file, cb$)=>\{$

cb$($null$,$ Date.now$()+\text{'}-\text{'}+$ file.originalname$)$; $//$ Unique filename

$\}$

$\})$;

const upload $=$ multer$(\{$ storage: storage $\})$;

$//$ MongoDB Connection

const mongoURI $=$ process.env.MONGODB$\_$URI $||$ "mongodb$+$srv:$//$:@cluster$0.$mongodb.net$/$gearInventory$?$retryWrites$=$true&w$=$majority";

mongoose.connect$($mongoURI$,\{$ useNewUrlParser: true, useUnifiedTopology: true $\})$

$.$then$(()=>$ console.log$("$MongoDB connected successfully"$))$

$.$catch$($err $=>$ console.error$("$MongoDB connection error:", err$))$;

$//$ Mongoose Schema and Model

const gearSchema $=$ new mongoose.Schema$(\{$

name: $\{$ type: String, required: true $\},$

brand: $\{$ type: String, required: true $\},$

price: $\{$ type: Number, required: true $\},$

img$\_$name: $\{$ type: String $\},$

rating: $\{$ type: Number $\},$

features: $[$String$]$

$\})$;

const Gear $=$ mongoose.model$(\text{'}$Gear$\text{'},$ gearSchema$)$;

$//$ Joi Schema for Validation

const itemSchema $=$ Joi.object$(\{$

name: Joi.string$().$required$(),$

brand: Joi.string$().$required$(),$

price: Joi.number$().$required$(),$

img$\_$name: Joi.string$().$optional$(),$

rating: Joi.number$().$optional$(),$

features: Joi.array$().$items$($Joi$.$string$()).$optional$()$

$\})$;

$//$ Serve Static HTML

app.get$(\text{'}/\text{'},($req$,$ res$)=>\{$

res.sendFile$(\_\_$dirname $+\text{'}/$index$.$html$\text{'})$;

$\})$;

$//$ Upload Route $($Handling file uploads$)$

app.post$(\text{'}/$api$/$upload$\text{'},$ upload.single$(\text{'}$gear$\text{'}),($req$,$ res$)=>\{$

if $(!$req.file$)\{$

return res.status$(400).$send$(\text{'}$No file uploaded.$\text{'})$;

$\}$

console.log$(\text{'}$File uploaded successfully:$\text{'},$ req.file$)$;

res.send$(\{$ message: 'File uploaded successfully!$\text{'},$ file: req.file $\})$;

$\})$;

$//$ Get all gear items

app.get$(\text{'}/$api$/$gear$\text{'},$ async $($req$,$ res$)=>\{$

try $\{$

const items $=$ await Gear.find$()$;

res.json$($items$)$;

$\}$ catch $($err$)\{$

console.error$(\text{'}$Error fetching gear items:$\text{'},$ err$)$;

res.status$(500).$json$(\{$ success: false, message: 'Failed to fetch gear items' $\})$;

$\}$

$\})$;

$//$ Create a new gear item

app.post$(\text{'}/$api$/$gear$\text{'},$ async $($req$,$ res$)=>\{$

const $\{$ error $\}=$ itemSchema.validate$($req$.$body$)$;

if $($error$)\{$

console.log$(\text{'}$Validation error:$\text{'},$ error.details$)$;

return res.status$(400).$json$(\{$ success: false, message: error.details$[0].$message $\})$;

$\}$

try $\{$

const newItem $=$ new Gear$($req$.$body$)$;

await newItem.save$()$;

console.log$(\text{'}$New gear item added:$\text{'},$ newItem$)$;

res.status$(201).$json$(\{$ success: true, newItem $\})$;

$\}$ catch $($err$)\{$

console.error$(\text{'}$Error saving gear item:$\text{'},$ err$)$;

res.status$(500).$json$(\{$ success: false, message: 'Failed to add gear item' $\})$;

$\}$

$\})$;

$//$ Update an existing gear item by ID

app.put$(\text{'}/$api$/$gear$/$:id$\text{'},$ async $($req$,$ res$)=>\{$

const $\{$ error $\}=$ itemSchema.validate$($req$.$body$)$;

if $($error$)\{$

console.log$(\text{'}$Validation error:$\text{'},$ error.details$)$;

return res.status$(400).$json$(\{$ success: false, message: error.details$[0].$message $\})$;

$\}$

try $\{$

const updatedItem $=$ await Gear.findByIdAndUpdate$($req$.$params.id$,$ req.body, $\{$ new: true $\})$;

if $(!$updatedItem$)\{$

return res.status$(404).$json$(\{$ success: false, message: 'Item not found' $\})$;

$\}$

console.log$(\text{'}$Gear item updated:$\text{'},$ updatedItem$)$;

res.json$(\{$ success: true, updatedItem $\})$;

$\}$ catch $($err$)\{$

console.error$(\text{'}$Error updating gear item:$\text{'},$ err$)$;

res.status$(500).$json$(\{$ success: false, message: 'Failed to update gear item' $\})$;

$\}$

$\})$;

$//$ Delete a gear item by ID

app.delete$(\text{'}/$api$/$gear$/$:id$\text{'},$ async $($req$,$ res$)=>\{$

try $\{$

const deletedItem $=$ await Gear.findByIdAndDelete$($req$.$params.id$)$;

if $(!$deletedItem$)\{$

return res.status$(404).$json$(\{$ success: false, message: 'Item not found' $\})$;

$\}$

console.log$(\text{'}$Gear item deleted:$\text{'},$ deletedItem$)$;

res.json$(\{$ success: true, message: 'Item deleted successfully' $\})$;

$\}$ catch $($err$)\{$

console.error$(\text{'}$Error deleting gear item:$\text{'},$ err$)$;

res.status$(500).$json$(\{$ success: false, message: 'Failed to delete gear item' $\})$;

$\}$

$\})$;

$//$ Listening on the desired port

const PORT $=$ process.env.PORT $||4000$;

app.listen$($PORT$,()=>\{$

console.log$(`$Listening on port $$\{$PORT$\}...`)$;

$\})$;