Hi Team,
I am trying to display files and attachment of account with next and pervious button. Need to display single file on layout after click need to open file in popup

apex 

public with sharing class ct_FileController { 

    @AuraEnabled
     public static List<ContentDocument> getFiles(Id recordId) {
       List<ContentDocument> documents = [SELECT Id,Title  FROM ContentDocument        
            WHERE Id IN (SELECT ContentDocumentId 
            FROM ContentDocumentLink 
            WHERE LinkedEntityId = :recordId)];        

        return documents;
    }
}

LWC Html 

<template>
    <lightning-card title="File Viewer" icon-name="custom:custom14">
        <div class="slds-m-around_medium">
          <p>hello </p>
            <p>{fileName}</p>
            <lightning-button label="Previous" class="slds-m-right_x-small" onclick={previous}></lightning-button>
            <lightning-button label="Next" class="slds-m-left_x-small" onclick={next}></lightning-button>
        </div>
    </lightning-card>
</template>

LWC JS 

import { LightningElement, api, wire } from 'lwc';
import  getFiles from '@salesforce/apex/FileController.getFiles';
import LightningPrompt from 'lightning/prompt';

export default class iframe extends LightningElement {
    @api recordId;
    fileIndex;
    fileName;
    @wire(getFiles, { recordId: '$recordId'})
    files;
    connectedCallback(){
        this.fileIndex = 0;    
        if(this.files.data){
            this.fileName = this.files.data[this.fileIndex].Name;
                        console.log("Line no 14 :::fileName" , fileName);
                console.log("Line no 15 :::files" , files.data);
        }
    }

    next(){
        LightningPrompt.open({
            message: 'Next button click',
            //theme defaults to "default"
            label: 'Please Respond', // this is the header text
            defaultValue: 'initial input value', //this is optional
        })
        if (this.fileIndex < this.files.data.length - 1) {
            this.fileIndex++;
            this.fileName = this.files.data[this.fileIndex].Name;
        }
    }

    previous(){
        LightningPrompt.open({
            message: 'Previous button click',
            //theme defaults to "default"
            label: 'Please Respond', // this is the header text
            defaultValue: 'initial input value', //this is optional
        })
        if (this.fileIndex > 0) {
            this.fileIndex--;
            this.fileName = this.files.data[this.fileIndex].Name;
        }
    }
}

But Iam unable to see file in layout need help to debug