bentopdf/src/js/logic/reverse-pages.ts

import { showLoader, hideLoader, showAlert } from '../ui.js';
import { downloadFile } from '../utils/helpers.js';
import { state } from '../state.js';

import { PDFDocument as PDFLibDocument } from 'pdf-lib';

export async function reversePages() {
    if (!state.pdfDoc) { showAlert('Error', 'PDF not loaded.'); return; }
    showLoader('Reversing page order...');
    try {
        const newPdf = await PDFLibDocument.create();
        const pageCount = state.pdfDoc.getPageCount();
        const reversedIndices = Array.from({ length: pageCount }, (_, i) => pageCount - 1 - i);

        const copiedPages = await newPdf.copyPages(state.pdfDoc, reversedIndices);
        copiedPages.forEach((page: any) => newPdf.addPage(page));

        const newPdfBytes = await newPdf.save();
        downloadFile(new Blob([new Uint8Array(newPdfBytes)], { type: 'application/pdf' }), 'reversed.pdf');
    } catch (e) {
        console.error(e);
        showAlert('Error', 'Could not reverse the PDF pages.');
    } finally {
        hideLoader();
    }
}