handle alphabetic suffixes

dlibrary/dlibrary.py

@@ -264,7 +264,7 @@ def unique_hierarchical_prefix_numbering(entries, start_point=0):
                 if len(numbering[idx]) > 1:
                     ents_idx = numbering.pop(idx)
                     next_layer_start = pos + NUMBER_REGEX.match(ents_idx[0].name[pos:]).end()
-                    sub_numbering = unique_hierarchical_prefix_numbering(ents_idx, start_point=next_layer_start)
+                    sub_numbering = unique_hierarchical_prefix_numbering(ents_idx, start_point=next_layer_start) or alphabetic_numbering(ents_idx, next_layer_start)
                     if not sub_numbering:
                         return None
                     for sub_idx in sub_numbering:
@@ -274,6 +274,22 @@ def unique_hierarchical_prefix_numbering(entries, start_point=0):
 
     return None
 
+def alphabetic_numbering(entries, start_point):
+    alphabetized = {}
+    for entry in entries:
+        ending = entry.stem[start_point:]
+        if len(ending) > 1:
+            return None
+        index = 0 if ending == '' else ord(ending.lower()) - ord('a')
+        if index in alphabetized:
+            return None
+        alphabetized[(index,)] = [entry]
+    indices = list(alphabetized.keys())
+    indices.sort()
+    if indices != [(i,) for i in range(len(indices))]:
+        return None
+    return alphabetized
+
 def link_ordered_files(ordering, dest, start_index):
     dest.mkdir(parents=True, exist_ok=True)