enh: keep a registry of already-used identifiers (and auto-generate new)

Resolves: #125.

sdcflows/fieldmaps.py

@@ -9,6 +9,9 @@
 from niworkflows.utils.bids import relative_to_root
 
 
+_unique_ids = set()
+
+
 class MetadataError(ValueError):
     """A better name for a specific value error."""
 
@@ -59,6 +62,27 @@ def _type_setter(obj, attribute, value):
     return value
 
 
+def _id_setter(obj, attribute, value):
+    """Ensure uniqueness of B0FieldIdentifier metadata."""
+    if obj.bids_id:
+        if obj.bids_id != value:
+            raise ValueError("Unique identifier is already set")
+        _unique_ids.add(value)
+        return value
+
+    if value is True:
+        value = f"auto_{len([el for el in _unique_ids if el.startswith('auto_')])}"
+    elif not value:
+        raise ValueError("Invalid unique identifier")
+
+    if value in _unique_ids:
+        raise ValueError("Unique identifier has been previously registered.")
+
+    _unique_ids.add(value)
+    return value
+
+
+
 @attr.s(slots=True)
 class FieldmapFile:
     """
@@ -253,6 +277,9 @@ class FieldmapEstimation:
     method = attr.ib(init=False, default=EstimatorType.UNKNOWN, on_setattr=_type_setter)
     """Flag indicating the estimator type inferred from the input sources."""
 
+    bids_id = attr.ib(default=None, kw_only=True, type=str, on_setattr=_id_setter)
+    """The unique ``B0FieldIdentifier`` field of this fieldmap."""
+
     def __attrs_post_init__(self):
         """Determine the inteded fieldmap estimation type and check for data completeness."""
         suffix_list = [f.suffix for f in self.sources]
@@ -349,3 +376,21 @@ def __attrs_post_init__(self):
         # No method has been identified -> fail.
         if self.method == EstimatorType.UNKNOWN:
             raise ValueError("Insufficient sources to estimate a fieldmap.")
+
+        if not self.bids_id:
+            bids_ids = set([
+                f.metadata.get("B0FieldIdentifier")
+                for f in self.sources if f.metadata.get("B0FieldIdentifier")
+            ])
+            if len(bids_ids) > 1:
+                raise ValueError(
+                    f"Multiple ``B0FieldIdentifier`` set: <{', '.join(bids_ids)}>"
+                )
+            elif not bids_ids:
+                self.bids_id = True
+            else:
+                self.bids_id = bids_ids.pop()
+        elif self.bids_id in _unique_ids:
+            raise ValueError("Unique identifier has been previously registered.")
+        else:
+            _unique_ids.add(self.bids_id)

sdcflows/tests/test_fieldmaps.py

@@ -54,9 +54,28 @@ def test_FieldmapEstimation(testdata_dir, inputfiles, method, nsources):
     """Test errors."""
     sub_dir = testdata_dir / "sub-01"
 
-    fe = FieldmapEstimation([sub_dir / f for f in inputfiles])
+    sources = [sub_dir / f for f in inputfiles]
+    fe = FieldmapEstimation(sources)
     assert fe.method == method
     assert len(fe.sources) == nsources
+    assert fe.bids_id is not None and fe.bids_id.startswith("auto_")
+
+    # Attempt to change bids_id
+    with pytest.raises(ValueError):
+        fe.bids_id = "other"
+
+    # Setting the same value should not raise
+    fe.bids_id = fe.bids_id
+
+    # Ensure duplicate B0FieldIdentifier are not accepted
+    with pytest.raises(ValueError):
+        FieldmapEstimation(sources, bids_id=fe.bids_id)
+
+    # B0FieldIdentifier can be generated manually
+    # Creating two FieldmapEstimation objects from the same sources SHOULD fail
+    # or be better handled in the future (see #129).
+    fe2 = FieldmapEstimation(sources, bids_id=f"no{fe.bids_id}")
+    assert fe2.bids_id and fe2.bids_id.startswith("noauto_")
 
 
 @pytest.mark.parametrize(
@@ -74,3 +93,38 @@ def test_FieldmapEstimationError(testdata_dir, inputfiles, errortype):
 
     with pytest.raises(errortype):
         FieldmapEstimation([sub_dir / f for f in inputfiles])
+
+
+def test_FieldmapEstimationIdentifier(testdata_dir):
+    """Check some use cases of B0FieldIdentifier."""
+    with pytest.raises(ValueError):
+        FieldmapEstimation([
+            FieldmapFile(testdata_dir / "sub-01" / "fmap/sub-01_fieldmap.nii.gz",
+                         metadata={"Units": "Hz", "B0FieldIdentifier": "fmap_0"}),
+            FieldmapFile(testdata_dir / "sub-01" / "fmap/sub-01_magnitude.nii.gz",
+                         metadata={"Units": "Hz", "B0FieldIdentifier": "fmap_1"})
+        ])  # Inconsistent identifiers
+
+    fe = FieldmapEstimation([
+        FieldmapFile(testdata_dir / "sub-01" / "fmap/sub-01_fieldmap.nii.gz",
+                     metadata={"Units": "Hz", "B0FieldIdentifier": "fmap_0"}),
+        FieldmapFile(testdata_dir / "sub-01" / "fmap/sub-01_magnitude.nii.gz",
+                     metadata={"Units": "Hz", "B0FieldIdentifier": "fmap_0"})
+    ])
+    assert fe.bids_id == "fmap_0"
+
+    with pytest.raises(ValueError):
+        FieldmapEstimation([
+            FieldmapFile(testdata_dir / "sub-01" / "fmap/sub-01_fieldmap.nii.gz",
+                         metadata={"Units": "Hz", "B0FieldIdentifier": "fmap_0"}),
+            FieldmapFile(testdata_dir / "sub-01" / "fmap/sub-01_magnitude.nii.gz",
+                         metadata={"Units": "Hz", "B0FieldIdentifier": "fmap_0"})
+        ])  # Consistent, but already exists
+
+    fe = FieldmapEstimation([
+        FieldmapFile(testdata_dir / "sub-01" / "fmap/sub-01_fieldmap.nii.gz",
+                     metadata={"Units": "Hz", "B0FieldIdentifier": "fmap_1"}),
+        FieldmapFile(testdata_dir / "sub-01" / "fmap/sub-01_magnitude.nii.gz",
+                     metadata={"Units": "Hz", "B0FieldIdentifier": "fmap_1"})
+    ])
+    assert fe.bids_id == "fmap_1"

sdcflows/workflows/base.py

@@ -41,20 +41,20 @@ def init_fmap_preproc_wf(
     ...     omp_nthreads=1,
     ...     output_dir="/tmp",
     ...     subject="1",
-    ... )
-    [FieldmapEstimation(sources=<4 files>, method=<EstimatorType.PHASEDIFF: 3>),
-     FieldmapEstimation(sources=<4 files>, method=<EstimatorType.PHASEDIFF: 3>),
-     FieldmapEstimation(sources=<3 files>, method=<EstimatorType.PHASEDIFF: 3>),
-     FieldmapEstimation(sources=<2 files>, method=<EstimatorType.PEPOLAR: 2>)]
+    ... )  # doctest: +ELLIPSIS
+    [FieldmapEstimation(sources=<4 files>, method=<EstimatorType.PHASEDIFF: 3>, bids_id='...'),
+     FieldmapEstimation(sources=<4 files>, method=<EstimatorType.PHASEDIFF: 3>, bids_id='...'),
+     FieldmapEstimation(sources=<3 files>, method=<EstimatorType.PHASEDIFF: 3>, bids_id='...'),
+     FieldmapEstimation(sources=<2 files>, method=<EstimatorType.PEPOLAR: 2>, bids_id='...')]
 
     >>> init_fmap_preproc_wf(
     ...     layout=layouts['testdata'],
     ...     omp_nthreads=1,
     ...     output_dir="/tmp",
     ...     subject="HCP101006",
-    ... )
-    [FieldmapEstimation(sources=<2 files>, method=<EstimatorType.PHASEDIFF: 3>),
-     FieldmapEstimation(sources=<2 files>, method=<EstimatorType.PEPOLAR: 2>)]
+    ... )  # doctest: +ELLIPSIS
+    [FieldmapEstimation(sources=<2 files>, method=<EstimatorType.PHASEDIFF: 3>, bids_id='...'),
+     FieldmapEstimation(sources=<2 files>, method=<EstimatorType.PEPOLAR: 2>, bids_id='...')]
 
     """
     from ..fieldmaps import FieldmapEstimation, FieldmapFile