Started migrating workflow controller

shared-operations/src/functions/common/detectEmptyPages.ts

@@ -0,0 +1,51 @@
+
+import { PdfFile } from '../../wrappers/PdfFile';
+import { PDFPageProxy } from "pdfjs-dist/types/src/display/api.js";
+import { Image } from 'image-js';
+
+import { getImagesOnPage } from "./getImagesOnPage.js";
+
+export async function detectEmptyPages(file: PdfFile, whiteThreashold: number): Promise<number[]> {
+    const pdfDoc = await file.getAsPdfJs();
+
+    const emptyPages: number[] = [];
+    for (let i = 1; i <= pdfDoc.numPages; i++) {
+        const page = await pdfDoc.getPage(i);
+        console.log("Checking page " + i);
+
+        if(!await hasText(page)) {
+            console.log(`Found text on Page ${i}, page is not empty`);
+            continue;
+        }
+
+        if(!await areImagesBlank(page, whiteThreashold)) {
+            console.log(`Found non white image on Page ${i}, page is not empty`);
+            continue;
+        }
+
+        console.log(`Page ${i} is empty.`);
+        emptyPages.push(i - 1);
+    }
+    return emptyPages;
+}
+
+async function hasText(page: PDFPageProxy): Promise<boolean> {
+    const textContent = await page.getTextContent();
+    return textContent.items.length === 0;
+}
+
+async function areImagesBlank(page: PDFPageProxy, threshold: number): Promise<boolean> {
+    const images = await getImagesOnPage(page);
+    for (const image of images) {
+        if(!await isImageBlank(image, threshold))
+            return false;
+    }
+    return true;
+}
+
+async function isImageBlank(image: string | Uint8Array | ArrayBuffer, threshold: number): Promise<boolean> {
+    var img = await Image.load(image);
+    var grey = img.grey();
+    var mean = grey.getMean();
+    return mean[0] <= threshold;
+}