Create a booklet from multiple pages

Closes #500

data/menu.ui

@@ -141,6 +141,10 @@ along with PDF Arranger.  If not, see <http://www.gnu.org/licenses/>.
           <attribute name="label" translatable="yes">Insert Blan_k Page</attribute>
           <attribute name="action">win.insert-blank-page</attribute>
         </item>
+        <item>
+          <attribute name="label" translatable="yes">Generate Booklet</attribute>
+          <attribute name="action">win.generate-booklet</attribute>
+        </item>
       </section>
     </submenu>
     <submenu>
@@ -331,6 +335,10 @@ along with PDF Arranger.  If not, see <http://www.gnu.org/licenses/>.
         <attribute name="label" translatable="yes">Insert Blan_k Page</attribute>
         <attribute name="action">win.insert-blank-page</attribute>
       </item>
+      <item>
+        <attribute name="label" translatable="yes">Generate Booklet</attribute>
+        <attribute name="action">win.generate-booklet</attribute>
+      </item>
     </section>
     <section>
       <submenu>

pdfarranger/exporter.py

@@ -30,14 +30,19 @@ def create_blank_page(tmpdir, size):
     Create a temporary PDF file with a single empty page.
     The size is in PDF unit (1/72 of inch).
     """
-    fd, filename = tempfile.mkstemp(suffix=".pdf", dir=tmpdir)
-    os.close(fd)
-    f = pikepdf.Pdf.new()
+    f, filename = make_tmp_file(tmpdir)
     f.add_blank_page(page_size=size)
     f.save(filename)
     return filename
 
 
+def make_tmp_file(tmpdir):
+    fd, filename = tempfile.mkstemp(suffix=".pdf", dir=tmpdir)
+    os.close(fd)
+    f = pikepdf.Pdf.new()
+    return f, filename
+
+
 def _mediabox(page, crop):
     """ Return the media box for a given page. """
     # PDF files which do not have mediabox default to Portrait Letter / ANSI A
@@ -193,3 +198,43 @@ def num_pages(filepath):
     npages = len(pdf.pages)
     pdf.close()
     return npages
+
+
+def generate_booklet(pdfqueue, tmp_dir, pages):
+    file, filename = make_tmp_file(tmp_dir)
+    content_dict = pikepdf.Dictionary({})
+    file_indexes = {p.nfile for p in pages}
+    source_files = {n: pikepdf.open(pdfqueue[n - 1].copyname) for n in file_indexes}
+    for i in range(len(pages)//2):
+        even = i % 2 == 0
+        first = pages[-i - 1 if even else i]
+        second = pages[i if even else -i - 1]
+
+        second_page_size = second.size_in_points()
+        first_page_size = first.size_in_points()
+        page_size = [max(second_page_size[0], first_page_size[0]) * 2,
+                     max(second_page_size[1], first_page_size[1])]
+        first_foreign = file.copy_foreign(source_files[first.nfile].pages[first.npage - 1])
+        second_foreign = file.copy_foreign(source_files[second.nfile].pages[second.npage - 1])
+
+        content_dict[f'/Page{i*2}'] = pikepdf.Page(first_foreign).as_form_xobject()
+        content_dict[f'/Page{i*2 + 1}'] = pikepdf.Page(second_foreign).as_form_xobject()
+
+        content_txt = (f'q 1 0 0 1 0 0 cm /Page{i*2} Do Q'
+                       f' q 1 0 0 1 {first_page_size[0]} 0 cm /Page{i*2 + 1} Do Q ')
+
+        newpage = pikepdf.Dictionary(
+                Type=pikepdf.Name.Page,
+                MediaBox=[0, 0, *page_size],
+                Resources=pikepdf.Dictionary(XObject=content_dict),
+                Contents=pikepdf.Stream(file, content_txt.encode())
+            )
+
+        # workaround for pikepdf <= 2.6.0. See https://github.com/pikepdf/pikepdf/issues/174
+        if pikepdf.__version__ < '2.7.0':
+            newpage = file.make_indirect(newpage)
+        file.pages.append(newpage)
+
+    file.save(filename)
+    return filename
+

pdfarranger/pdfarranger.py

@@ -352,6 +352,7 @@ def __create_actions(self):
             ('select-same-format', self.on_action_select, 'i'),
             ('about', self.about_dialog),
             ("insert-blank-page", self.insert_blank_page),
+            ("generate-booklet", self.generate_booklet),
         ])
 
         main_menu = self.uiXML.get_object("main_menu_button")
@@ -374,11 +375,47 @@ def insert_blank_page(self, _action, _option, _unknown):
             size = model[selection[-1]][0].size_in_points()
         page_size = croputils.BlankPageDialog(size, self.window).run_get()
         if page_size is not None:
-            adder = PageAdder(self)
-            if len(selection) > 0:
-                adder.move(Gtk.TreeRowReference.new(model, selection[-1]), False)
-            adder.addpages(exporter.create_blank_page(self.tmp_dir, page_size))
-            adder.commit(select_added=False, add_to_undomanager=True)
+            self._insert_pages(model, exporter.create_blank_page(self.tmp_dir, page_size), selection)
+
+    def _insert_pages(self, model, file, selection):
+        adder = PageAdder(self)
+        if len(selection) > 0:
+            adder.move(Gtk.TreeRowReference.new(model, selection[-1]), False)
+        adder.addpages(file)
+        adder.commit(select_added=False, add_to_undomanager=True)
+
+    def generate_booklet(self, _, __, ___):
+        self.undomanager.commit("generate booklet")
+        model = self.iconview.get_model()
+
+        selection = self.iconview.get_selected_items()
+        selection.sort(key=lambda x: x.get_indices()[0])
+        ref_list = [Gtk.TreeRowReference.new(model, path)
+                    for path in selection]
+        pages = [model.get_value(model.get_iter(ref.get_path()), 0)
+                 for ref in ref_list]
+
+        # We need a multiple of 4
+        blank_page_count = 0 if len(pages) % 4 == 0 else 4 - len(pages) % 4
+        if blank_page_count > 0:
+            file = exporter.create_blank_page(self.tmp_dir, pages[0].size)
+            with self.model_lock:
+                for _ in range(blank_page_count):
+                    self._insert_pages(model, file, selection)
+                    added_page_index = selection[-1].get_indices()[-1] + 1
+                    # Fetch the additional blank pages and remove them from the model.
+                    added_page = model.get_value(model.get_iter(added_page_index), 0)
+                    pages.append(added_page)
+                    model.remove(model.get_iter(added_page_index))
+
+        self.clear_selected()
+
+        adder = PageAdder(self)
+        booklet = exporter.generate_booklet(self.pdfqueue, self.tmp_dir, pages)
+        adder.addpages(booklet)
+        adder.commit(False, False)
+        self.silent_render()
+
 
     @staticmethod
     def __create_filters(file_type_list):
@@ -1008,9 +1045,10 @@ def on_action_add_doc_activate(self, _action, _param, _unknown):
             adder.commit(select_added=False, add_to_undomanager=True)
         chooser.destroy()
 
-    def clear_selected(self):
+    def clear_selected(self, add_to_undomanager=True):
         """Removes the selected elements in the IconView"""
-        self.undomanager.commit("Delete")
+        if add_to_undomanager:
+            self.undomanager.commit("Delete")
         model = self.iconview.get_model()
         selection = self.iconview.get_selected_items()
         selection.sort(reverse=True)
@@ -1701,6 +1739,7 @@ def iv_selection_changed_event(self, _iconview=None, move_cursor_event=False):
             ("select-same-file", ne),
             ("select-same-format", ne),
             ("crop-white-borders", ne),
+            ("generate-booklet", ne),
         ]:
             self.window.lookup_action(a).set_enabled(e)
         self.__update_statusbar()