Add minimum column width as an option to reading order (#2)

* CHANGE: Improve reading order to be able to take into account a minimum column width (default 5% of page)

* linter compatibility fixes

docs/modules/reading-order-detection-module.md

@@ -22,6 +22,11 @@ First, the algorithm will try to find possible vertical cuts in the page between
 
 Good
 
+## Options
+
+minColumnWidthInPagePercent : The minimal column width in % of the page width
+minVerticalGapWidth : The minimal gap width in points
+
 ## Limitations
 
 - It sometimes fails if bounding boxes are too far from each others.

server/src/modules/ReadingOrderDetectionModule.ts

@@ -26,16 +26,19 @@ import { Module } from './Module';
  */
 
 interface Options {
-	minWidth?: number;
+	minColumnWidthInPagePercent?: number;
+	minVerticalGapWidth?: number;
 }
 
 const defaultOptions: Options = {
-	minWidth: 5,
+	minVerticalGapWidth: 5,
+	minColumnWidthInPagePercent: 5,
 };
 
 export class ReadingOrderDetectionModule extends Module<Options> {
 	public static moduleName = 'reading-order-detection';
 	private order: number = 0;
+	private currentPageMinColumnWidth: number = 5;
 
 	constructor(options?: Options) {
 		super(options, defaultOptions);
@@ -47,6 +50,11 @@ export class ReadingOrderDetectionModule extends Module<Options> {
 			const elements: Element[] = page.elements.filter(Element.hasBoundingBox);
 
 			this.order = 0;
+			// The min width is actually as a % of page width
+			this.currentPageMinColumnWidth = Math.trunc(
+				(this.options.minColumnWidthInPagePercent / 100) * page.width,
+			);
+
 			this.process(elements);
 
 			elements.sort(utils.sortElementsByOrder);
@@ -184,7 +192,7 @@ export class ReadingOrderDetectionModule extends Module<Options> {
 
 				elementsRest.forEach(e => {
 					if (
-						e.left <= rightmost + this.options.minWidth &&
+						e.left <= rightmost + this.options.minVerticalGapWidth &&
 						e.left >= startGroup &&
 						!group.includes(e)
 					) {
@@ -199,6 +207,39 @@ export class ReadingOrderDetectionModule extends Module<Options> {
 			group = [];
 		}
 
+		// Merge to right to small collumn
+
+		for (let i = 0; i < elementsGroups.length; ++i) {
+			// calculate group width
+			const columnWidth = this.calcualteGroupWidth(elementsGroups[i]);
+			if (columnWidth < this.currentPageMinColumnWidth) {
+				if (i < elementsGroups.length - 1) {
+					// default Right merge
+					elementsGroups[i + 1] = [...elementsGroups[i], ...elementsGroups[i + 1]];
+					elementsGroups.splice(i--, 1);
+				} else if (i > 0) {
+					// if no rightMerge possible try left merge
+					elementsGroups[i - 1] = [...elementsGroups[i - 1], ...elementsGroups[i]];
+					elementsGroups.splice(i--, 1);
+				}
+			}
+		}
+
 		return elementsGroups;
 	}
+
+	private calcualteGroupWidth(elements: Element[]) {
+		let minX = elements[0].left;
+		let maxX = elements[0].left + elements[0].width;
+
+		for (let i = 1; i < elements.length; ++i) {
+			if (elements[i].left < minX) {
+				minX = elements[i].left;
+			}
+			if (elements[i].left + elements[i].width > maxX) {
+				maxX = elements[i].left + elements[i].width;
+			}
+		}
+		return maxX - minX;
+	}
 }