Add Odd-Even Merge operation mode (#1445)

* Add ODD_EVEN_MERGE sort type

* Add process method to merge odd and even PDF pages

* Add test cases for Odd-Even merge method

* Add Odd-Even Merge mode in PDF Organizer webpage

This also add a new translatable text message variable pdfOrganiser.mode.10 with translation for english and german

* Add ODD_EVEN_MERGE documentation to RearrangePagesRequest

* Add english translation for pdfOrganiser.mode.10

---------

Co-authored-by: Anthony Stirling <77850077+Frooodle@users.noreply.github.com>

src/main/java/stirling/software/SPDF/controller/api/RearrangePagesPDFController.java

@@ -145,6 +145,28 @@ public class RearrangePagesPDFController {
         return newPageOrder;
     }
 
+    /**
+     * Rearrange pages in a PDF file by merging odd and even pages. The first half of the pages will
+     * be the odd pages, and the second half will be the even pages as input. <br>
+     * This method is visible for testing purposes only.
+     *
+     * @param totalPages Total number of pages in the PDF file.
+     * @return List of page numbers in the new order. The first page is 0.
+     */
+    List<Integer> oddEvenMerge(int totalPages) {
+        List<Integer> newPageOrderZeroBased = new ArrayList<>();
+        int numberOfOddPages = (totalPages + 1) / 2;
+
+        for (int oneBasedIndex = 1; oneBasedIndex < (numberOfOddPages + 1); oneBasedIndex++) {
+            newPageOrderZeroBased.add((oneBasedIndex - 1));
+            if (numberOfOddPages + oneBasedIndex <= totalPages) {
+                newPageOrderZeroBased.add((numberOfOddPages + oneBasedIndex - 1));
+            }
+        }
+
+        return newPageOrderZeroBased;
+    }
+
     private List<Integer> processSortTypes(String sortTypes, int totalPages) {
         try {
             SortTypes mode = SortTypes.valueOf(sortTypes.toUpperCase());
@@ -159,6 +181,8 @@ public class RearrangePagesPDFController {
                     return sideStitchBooklet(totalPages);
                 case ODD_EVEN_SPLIT:
                     return oddEvenSplit(totalPages);
+                case ODD_EVEN_MERGE:
+                    return oddEvenMerge(totalPages);
                 case REMOVE_FIRST:
                     return removeFirst(totalPages);
                 case REMOVE_LAST:

src/main/java/stirling/software/SPDF/model/SortTypes.java

@@ -6,6 +6,7 @@ public enum SortTypes {
     BOOKLET_SORT,
     SIDE_STITCH_BOOKLET_SORT,
     ODD_EVEN_SPLIT,
+    ODD_EVEN_MERGE,
     REMOVE_FIRST,
     REMOVE_LAST,
     REMOVE_FIRST_AND_LAST,

src/main/java/stirling/software/SPDF/model/api/general/RearrangePagesRequest.java

@@ -19,6 +19,7 @@ public class RearrangePagesRequest extends PDFWithPageNums {
                             + "DUPLEX_SORT: Sorts pages as if all fronts were scanned then all backs in reverse (1, n, 2, n-1, ...). "
                             + "BOOKLET_SORT: Arranges pages for booklet printing (last, first, second, second last, ...).\n"
                             + "ODD_EVEN_SPLIT: Splits and arranges pages into odd and even numbered pages.\n"
+                            + "ODD_EVEN_MERGE: Merges pages and organises them alternately into odd and even pages.\n"
                             + "REMOVE_FIRST: Removes the first page.\n"
                             + "REMOVE_LAST: Removes the last page.\n"
                             + "REMOVE_FIRST_AND_LAST: Removes both the first and the last pages.\n")