[ENH] Clean code

src/clinicaio/models/bids/__init__.py

@@ -0,0 +1,7 @@
+from ._base import Index, Label, Suffix
+
+__all__ = [
+    "Label",
+    "Index",
+    "Suffix",
+]

src/clinicaio/models/bids/_base.py

@@ -0,0 +1,54 @@
+from collections import UserString
+from enum import Enum
+from typing import Optional, Union
+
+__all__ = [
+    "Label",
+    "Index",
+    "Suffix",
+]
+
+
+class Label(UserString):
+    """Defines a label as defined in the BIDS specifications (i.e. an alphanumeric string)."""
+
+    def __init__(self, value: Union[str, Enum]):
+        super().__init__(self.validate(value))
+
+    @classmethod
+    def validate(cls, value: Union[str, Enum]) -> str:
+        if isinstance(value, Enum):
+            return value.value
+        elif isinstance(value, str) and value.isalnum():
+            return value
+        raise ValueError(
+            f"Label '{value}' is not a valid BIDS label: it must be string composed only by letters and/or numbers."
+        )
+
+
+Suffix = Label
+
+
+class Index(UserString):
+    """Defines an index as defined in the BIDS specifications as a positive integer with padding logic."""
+
+    def __init__(self, value: int, length_as_string: Optional[int] = None):
+        super().__init__(self.validate(value, length_as_string))
+
+    @classmethod
+    def validate(cls, value: int, length_as_string: Optional[int] = None) -> str:
+        if not isinstance(value, int) or value < 0:
+            raise ValueError(
+                f"Index '{value}' is not a valid BIDS index: it must be a non-negative integer."
+            )
+        if length_as_string is None:
+            length_as_string = len(str(value))
+        if length_as_string <= 0:
+            raise ValueError(
+                f"The length of an Index should be at least 1, {length_as_string} was provided."
+            )
+        if len(str(value)) > length_as_string:
+            raise ValueError(
+                f"Cannot set index with value {value} with a length of {length_as_string}."
+            )
+        return str(value).zfill(length_as_string)