bentopdf/src/js/logic/invert-colors.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 invertColors() {
    if (!state.pdfDoc) { showAlert('Error', 'PDF not loaded.'); return; }
    showLoader('Inverting PDF colors...');
    try {
        const newPdfDoc = await PDFLibDocument.create();
        const pdfBytes = await state.pdfDoc.save();
        // @ts-expect-error TS(2304) FIXME: Cannot find name 'pdfjsLib'.
        const pdfjsDoc = await pdfjsLib.getDocument({ data: pdfBytes }).promise;

        for (let i = 1; i <= pdfjsDoc.numPages; i++) {
            const page = await pdfjsDoc.getPage(i);
            const viewport = page.getViewport({ scale: 1.5 });
            const canvas = document.createElement('canvas');
            canvas.width = viewport.width;
            canvas.height = viewport.height;
            const ctx = canvas.getContext('2d');
            await page.render({ canvasContext: ctx, viewport }).promise;

            const imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
            const data = imageData.data;
            for (let j = 0; j < data.length; j += 4) {
                data[j] = 255 - data[j];     // red
                data[j + 1] = 255 - data[j + 1]; // green
                data[j + 2] = 255 - data[j + 2]; // blue
            }
            ctx.putImageData(imageData, 0, 0);

            const pngImageBytes = await new Promise(resolve => canvas.toBlob(blob => {
                const reader = new FileReader();
                // @ts-expect-error TS(2769) FIXME: No overload matches this call.
                reader.onload = () => resolve(new Uint8Array(reader.result));
                reader.readAsArrayBuffer(blob);
            }, 'image/png'));
            
            const image = await newPdfDoc.embedPng(pngImageBytes as ArrayBuffer);
            const newPage = newPdfDoc.addPage([image.width, image.height]);
            newPage.drawImage(image, { x: 0, y: 0, width: image.width, height: image.height });
        }
        const newPdfBytes = await newPdfDoc.save();
        downloadFile(new Blob([newPdfBytes], { type: 'application/pdf' }), 'inverted.pdf');
    } catch (e) {
        console.error(e);
        showAlert('Error', 'Could not invert PDF colors.');
    } finally {
        hideLoader();
    }
}