When merging books add an option to store discarded or replaced covers as an alternate cover in the data folder of the target book. Fixes #2071033 [[Enhancement] Merging Books: Copy cover of second book to data files](https://bugs.launchpad.net/calibre/+bug/2071033)

src/calibre/db/cache.py

@@ -28,7 +28,7 @@ from calibre.customize.ui import run_plugins_on_import, run_plugins_on_postadd,
 from calibre.db import SPOOL_SIZE, _get_next_series_num_for_list
 from calibre.db.annotations import merge_annotations
 from calibre.db.categories import get_categories
-from calibre.db.constants import NOTES_DIR_NAME
+from calibre.db.constants import COVER_FILE_NAME, DATA_DIR_NAME, NOTES_DIR_NAME
 from calibre.db.errors import NoSuchBook, NoSuchFormat
 from calibre.db.fields import IDENTITY, InvalidLinkTable, create_field
 from calibre.db.lazy import FormatMetadata, FormatsList, ProxyMetadata
@@ -3346,12 +3346,13 @@ class Cache:
         self.backend.copy_extra_file_to(book_id, path, relpath, stream_or_path)
 
     @write_api
-    def merge_book_metadata(self, dest_id, src_ids, replace_cover=False):
+    def merge_book_metadata(self, dest_id, src_ids, replace_cover=False, save_alternate_cover=False):
         dest_mi = self.get_metadata(dest_id)
         merged_identifiers = self._field_for('identifiers', dest_id) or {}
         orig_dest_comments = dest_mi.comments
         dest_cover = orig_dest_cover = self.cover(dest_id)
         had_orig_cover = bool(dest_cover)
+        alternate_covers = []
         from calibre.utils.date import is_date_undefined
 
         def is_null_date(x):
@@ -3379,8 +3380,14 @@ class Cache:
             if not dest_cover or replace_cover:
                 src_cover = self.cover(src_id)
                 if src_cover:
+                    if save_alternate_cover and dest_cover:
+                        alternate_covers.append(dest_cover)
                     dest_cover = src_cover
                     replace_cover = False
+            elif save_alternate_cover:
+                src_cover = self.cover(src_id)
+                if src_cover:
+                    alternate_covers.append(src_cover)
             if not dest_mi.publisher:
                 dest_mi.publisher = src_mi.publisher
             if not dest_mi.rating:
@@ -3401,6 +3408,17 @@ class Cache:
 
         if dest_cover and (not had_orig_cover or dest_cover is not orig_dest_cover):
             self._set_cover({dest_id: dest_cover})
+        if alternate_covers:
+            existing = {x[0] for x in self._list_extra_files(dest_id)}
+            h, ext = os.path.splitext(COVER_FILE_NAME)
+            template = f'{DATA_DIR_NAME}/{h}-{{:03d}}{ext}'
+            for cdata in alternate_covers:
+                for i in range(1, 1000):
+                    q = template.format(i)
+                    if q not in existing:
+                        existing.add(q)
+                        self._add_extra_files(dest_id, {q: BytesIO(cdata)}, replace=False, auto_rename=True)
+                        break
 
         for key in self.field_metadata:  # loop thru all defined fields
             fm = self.field_metadata[key]

src/calibre/gui2/actions/edit_metadata.py

@@ -579,7 +579,7 @@ class EditMetadataAction(InterfaceActionWithLibraryDrop):
             if d.merge_formats:
                 self.add_formats(dest_id, self.formats_for_ids(list(src_ids)))
             if d.merge_metadata:
-                self.merge_metadata(dest_id, src_ids, replace_cover=d.replace_cover)
+                self.merge_metadata(dest_id, src_ids, replace_cover=d.replace_cover, save_alternate_cover=d.save_alternate_cover)
                 if d.replace_cover:
                     covers_replaced = True
             if d.delete_books:
@@ -613,16 +613,17 @@ class EditMetadataAction(InterfaceActionWithLibraryDrop):
         title = mi.title
         hpos = self.gui.library_view.horizontalScrollBar().value()
         if safe_merge:
-            if not confirm_merge('<p>'+_(
+            confirmed, save_alternate_cover = confirm_merge('<p>'+_(
                 'Book formats and metadata from the selected books '
                 'will be added to the <b>first selected book</b> (%s).<br> '
                 'The second and subsequently selected books will not '
                 'be deleted or changed.<br><br>'
                 'Please confirm you want to proceed.')%title + '</p>',
-                'merge_books_safe', self.gui, mi):
+                'merge_books_safe', self.gui, mi, ask_about_save_alternate_cover=True)
+            if not confirmed:
                 return
             self.add_formats(dest_id, self.formats_for_books(rows))
-            self.merge_metadata(dest_id, src_ids)
+            self.merge_metadata(dest_id, src_ids, save_alternate_cover=save_alternate_cover)
         elif merge_only_formats:
             if not confirm_merge('<p>'+_(
                 'Book formats from the selected books will be merged '
@@ -640,7 +641,7 @@ class EditMetadataAction(InterfaceActionWithLibraryDrop):
             self.add_formats(dest_id, self.formats_for_books(rows))
             self.delete_books_after_merge(src_ids)
         else:
-            if not confirm_merge('<p>'+_(
+            confirmed, save_alternate_cover = confirm_merge('<p>'+_(
                 'Book formats and metadata from the selected books will be merged '
                 'into the <b>first selected book</b> (%s).<br><br>'
                 'After being merged, the second and '
@@ -649,10 +650,11 @@ class EditMetadataAction(InterfaceActionWithLibraryDrop):
                 'and any duplicate formats in the second and subsequently selected books '
                 'will be permanently <b>deleted</b> from your calibre library.<br><br>  '
                 'Are you <b>sure</b> you want to proceed?')%title + '</p>',
-                'merge_books', self.gui, mi):
+                'merge_books', self.gui, mi, ask_about_save_alternate_cover=True)
+            if not confirmed:
                 return
             self.add_formats(dest_id, self.formats_for_books(rows))
-            self.merge_metadata(dest_id, src_ids)
+            self.merge_metadata(dest_id, src_ids, save_alternate_cover=save_alternate_cover)
             self.merge_data_files(dest_id, src_ids)
             self.delete_books_after_merge(src_ids)
             # leave the selection highlight on first selected book
@@ -709,8 +711,8 @@ class EditMetadataAction(InterfaceActionWithLibraryDrop):
     def delete_books_after_merge(self, ids_to_delete):
         self.gui.library_view.model().delete_books_by_id(ids_to_delete)
 
-    def merge_metadata(self, dest_id, src_ids, replace_cover=False):
+    def merge_metadata(self, dest_id, src_ids, replace_cover=False, save_alternate_cover=False):
-        self.gui.current_db.new_api.merge_book_metadata(dest_id, src_ids, replace_cover)
+        self.gui.current_db.new_api.merge_book_metadata(dest_id, src_ids, replace_cover, save_alternate_cover=save_alternate_cover)
     # }}}
 
     def edit_device_collections(self, view, oncard=None):

src/calibre/gui2/dialogs/confirm_merge.py

@@ -50,8 +50,9 @@ class Target(QTextBrowser):
 
 class ConfirmMerge(Dialog):
 
-    def __init__(self, msg, name, parent, mi):
+    def __init__(self, msg, name, parent, mi, ask_about_save_alternate_cover=False):
         self.msg, self.mi, self.conf_name = msg, mi, name
+        self.ask_about_save_alternate_cover = ask_about_save_alternate_cover
         Dialog.__init__(self, _('Are you sure?'), 'confirm-merge-dialog', parent)
         needed, sz = self.sizeHint(), self.size()
         if needed.width() > sz.width() or needed.height() > sz.height():
@@ -71,6 +72,13 @@ class ConfirmMerge(Dialog):
         self.la = la = QLabel(self.msg)
         la.setWordWrap(True)
         l.addWidget(la)
+        self.save_alternate_cover_cb = c = QCheckBox(_('Save replaced or discarded &cover'), self)
+        c.setToolTip(_('Save the replaced or discarded cover in the data files associated with the target book as an alternate cover'))
+        c.setObjectName('choose-merge-cb-save_alternate_cover')
+        c.setChecked(bool(gprefs.get(c.objectName(), False)))
+        l.addWidget(c)
+        c.setVisible(self.ask_about_save_alternate_cover)
+        c.toggled.connect(self.alternate_covers_toggled)
         self.confirm = c = QCheckBox(_('Show this confirmation again'), self)
         c.setChecked(True)
         c.stateChanged.connect(self.toggle)
@@ -79,6 +87,9 @@ class ConfirmMerge(Dialog):
         self.right = r = Target(self.mi, self)
         s.addWidget(r)
 
+    def alternate_covers_toggled(self):
+        gprefs.set(self.save_alternate_cover_cb.objectName(), self.save_alternate_cover_cb.isChecked())
+
     def toggle(self):
         dynamic[confirm_config_name(self.conf_name)] = self.confirm.isChecked()
 
@@ -88,12 +99,12 @@ class ConfirmMerge(Dialog):
         return ans
 
 
-def confirm_merge(msg, name, parent, mi):
+def confirm_merge(msg, name, parent, mi, ask_about_save_alternate_cover=False):
     config_set = dynamic
     if not config_set.get(confirm_config_name(name), True):
         return True
-    d = ConfirmMerge(msg, name, parent, mi)
+    d = ConfirmMerge(msg, name, parent, mi, ask_about_save_alternate_cover)
-    return d.exec() == QDialog.DialogCode.Accepted
+    return d.exec() == QDialog.DialogCode.Accepted, d.save_alternate_cover_cb.isChecked()
 
 
 class ChooseMerge(Dialog):
@@ -116,11 +127,11 @@ class ChooseMerge(Dialog):
         w.fl = fl = FlowLayout()
         l.addLayout(fl)
 
-        def cb(name, text, tt=''):
+        def cb(name, text, tt='', defval=True):
             ans = QCheckBox(text)
             fl.addWidget(ans)
             prefs_key = ans.prefs_key = 'choose-merge-cb-' + name
-            ans.setChecked(gprefs.get(prefs_key, True))
+            ans.setChecked(gprefs.get(prefs_key, defval))
             connect_lambda(ans.stateChanged, self, lambda self, state: self.state_changed(getattr(self, name), state), type=Qt.ConnectionType.QueuedConnection)
             if tt:
                 ans.setToolTip(tt)
@@ -135,6 +146,8 @@ class ChooseMerge(Dialog):
             'Delete the selected books after merging'))
         cb('replace_cover', _('Replace existing cover'), _(
             'Replace the cover in the target book with the dragged cover'))
+        cb('save_alternate_cover', _('Save alternate cover'), _(
+            'Save the replaced or discarded cover in the data files associated with the target book as an alternate cover'), defval=False)
         l.addStretch(10)
         self.msg = la = QLabel(self)
         la.setWordWrap(True)
@@ -197,7 +210,7 @@ class ChooseMerge(Dialog):
     def merge_type(self):
         return MergeData(
             self.merge_metadata.isChecked(), self.merge_formats.isChecked(), self.delete_books.isChecked(),
-            self.replace_cover.isChecked(),
+            self.replace_cover.isChecked(), self.save_alternate_cover.isChecked(),
         )
 
 
@@ -206,6 +219,7 @@ class MergeData(NamedTuple):
     merge_formats: bool = False
     delete_books: bool = False
     replace_cover: bool = False
+    save_alternate_cover: bool = False
 
 
 def merge_drop(dest_id, src_ids, gui):