Split pages support n function and other stuff

src/main/java/stirling/software/SPDF/utils/GeneralUtils.java

@@ -1,5 +1,8 @@
 package stirling.software.SPDF.utils;
 
+import java.util.ArrayList;
+import java.util.List;
+
 public class GeneralUtils {
 
 	public static Long convertSizeToBytes(String sizeStr) {
@@ -27,4 +30,62 @@ public class GeneralUtils {
 	    return null;
 	}
 
+	public static List<Integer> parsePageList(String[] pageOrderArr, int totalPages) {
+	    List<Integer> newPageOrder = new ArrayList<>();
+
+	    // loop through the page order array
+	    for (String element : pageOrderArr) {
+	        // check if the element contains a range of pages
+	        if (element.matches("\\d*n\\+?-?\\d*|\\d*\\+?n")) {
+	            // Handle page order as a function
+	            int coefficient = 0;
+	            int constant = 0;
+	            boolean coefficientExists = false;
+	            boolean constantExists = false;
+
+	            if (element.contains("n")) {
+	                String[] parts = element.split("n");
+	                if (!parts[0].equals("") && parts[0] != null) {
+	                    coefficient = Integer.parseInt(parts[0]);
+	                    coefficientExists = true;
+	                }
+	                if (parts.length > 1 && !parts[1].equals("") && parts[1] != null) {
+	                    constant = Integer.parseInt(parts[1]);
+	                    constantExists = true;
+	                }
+	            } else if (element.contains("+")) {
+	                constant = Integer.parseInt(element.replace("+", ""));
+	                constantExists = true;
+	            }
+
+	            for (int i = 1; i <= totalPages; i++) {
+	                int pageNum = coefficientExists ? coefficient * i : i;
+	                pageNum += constantExists ? constant : 0;
+
+	                if (pageNum <= totalPages && pageNum > 0) {
+	                    newPageOrder.add(pageNum - 1);
+	                }
+	            }
+	        } else if (element.contains("-")) {
+	            // split the range into start and end page
+	            String[] range = element.split("-");
+	            int start = Integer.parseInt(range[0]);
+	            int end = Integer.parseInt(range[1]);
+	            // check if the end page is greater than total pages
+	            if (end > totalPages) {
+	                end = totalPages;
+	            }
+	            // loop through the range of pages
+	            for (int j = start; j <= end; j++) {
+	                // print the current index
+	                newPageOrder.add(j - 1);
+	            }
+	        } else {
+	            // if the element is a single page
+	            newPageOrder.add(Integer.parseInt(element) - 1);
+	        }
+	    }
+
+	    return newPageOrder;
+	}
 }