BF+TST: Handle case with extra-spatial index that is unique per frame

Not sure if this ever actually happens in real multiframe data, but
it does in non-multiframe and I can imagine if a
DimensionIndexSequence element refrences a per-frame AcquisitionTime
then this could happen.

Author: moloney

nibabel/nicom/dicomwrappers.py

@@ -598,22 +598,35 @@ def image_shape(self):
                 unique = np.unique(row)
                 if len(unique) != count:
                     raise WrapperError("Number of slice indices and positions don't match")
+            elif count == n_frames:
+                if shape[-1] == "remaining":
+                    raise WrapperError("At most one index have ambiguous size")
+                shape.append("remaining")
+                continue
             new_parts, leftover = divmod(curr_parts, count)
-            allowed_val_counts = [new_parts * frames_per_part]
-            if row_idx != slice_dim_idx:
-                # Except for the slice dim, having a unique value for each frame is valid
-                allowed_val_counts.append(n_frames)
+            expected = new_parts * frames_per_part
             if (
                 leftover != 0 or 
-                any(np.count_nonzero(row == val) not in allowed_val_counts for val in unique)
+                any(np.count_nonzero(row == val) != expected for val in unique)
             ):
                 if row_idx == slice_dim_idx:
                     raise WrapperError("Missing slices from multiframe")
                 del_indices[row_idx] = count
                 continue
+            if shape[-1] == "remaining":
+                shape[-1] = new_parts
+                frames_per_part *= shape[-1]
+                new_parts = 1
             frames_per_part *= count
             shape.append(count)
             curr_parts = new_parts
+        if shape[-1] == "remaining":
+            if curr_parts > 1:
+                shape[-1] = curr_parts
+                curr_parts = 1
+            else:
+                del_indices[len(shape)] = 1
+                shape = shape[:-1]
         if del_indices:
             if curr_parts > 1:
                 ns_failed = [k for k, v in del_indices.items() if v != 1]

nibabel/nicom/tests/test_dicomwrappers.py

@@ -623,6 +623,28 @@ def test_shape(self):
                    (1, 1, 2, 2), (1, 2, 2, 2))
         fake_mf.update(fake_shape_dependents(div_seq, sid_dim=0))
         assert MFW(fake_mf).image_shape == (32, 64, 2, 3)
+        # Test invalid 4D indices
+        div_seq = ((1, 1, 1), (1, 2, 1), (1, 1, 2), (1, 2, 2), (1, 1, 3), (1, 2, 4))
+        fake_mf.update(fake_shape_dependents(div_seq, sid_dim=0))
+        with pytest.raises(didw.WrapperError):
+            MFW(fake_mf).image_shape
+        div_seq = ((1, 1, 1), (1, 2, 1), (1, 1, 2), (1, 2, 2), (1, 1, 3), (1, 2, 2))
+        fake_mf.update(fake_shape_dependents(div_seq, sid_dim=0))
+        with pytest.raises(didw.WrapperError):
+            MFW(fake_mf).image_shape
+        # Time index that is unique to each frame
+        div_seq = ((1, 1, 1), (1, 2, 2), (1, 1, 3), (1, 2, 4), (1, 1, 5), (1, 2, 6))
+        fake_mf.update(fake_shape_dependents(div_seq, sid_dim=0))
+        assert MFW(fake_mf).image_shape == (32, 64, 2, 3)
+        div_seq = ((1, 1, 1, 1), (1, 2, 2, 1), 
+                   (1, 1, 3, 1), (1, 2, 4, 1),
+                   (1, 1, 5, 1), (1, 2, 6, 1),
+                   (1, 1, 7, 2), (1, 2, 8, 2),
+                   (1, 1, 9, 2), (1, 2, 10, 2),
+                   (1, 1, 11, 2), (1, 2, 12, 2),
+                  )
+        fake_mf.update(fake_shape_dependents(div_seq, sid_dim=0))
+        assert MFW(fake_mf).image_shape == (32, 64, 2, 3, 2)
 
     def test_iop(self):
         # Test Image orient patient for multiframe