Add function to invert constraints and ranges #91

CHANGELOG.rst

@@ -2,6 +2,12 @@ Changelog
 =========
 
 
+Version v30.9.1
+----------------
+
+- Add inverse function to VersionRange.
+
+
 Version v30.9.0
 ----------------
 

src/univers/version_range.py

@@ -25,6 +25,16 @@ class InvalidVersionRange(Exception):
     """
 
 
+INVERTED_COMPARATORS = {
+    ">=": "<",
+    "<=": ">",
+    "!=": "=",
+    "<": ">=",
+    ">": "<=",
+    "=": "!=",
+}
+
+
 @attr.s(frozen=True, order=False, eq=True, hash=True)
 class VersionRange:
     """
@@ -164,6 +174,33 @@ def from_versions(cls, sequence):
             constraints.append(constraint)
         return cls(constraints=constraints)
 
+    def invert(self):
+        """
+        Return the inverse of this VersionRange. For example, if this range is
+        ">=1.0.0", the inverse is "<1.0.0".
+        >>> VersionRange.from_string("vers:npm/>=1.0.0").invert()
+        NpmVersionRange(constraints=(VersionConstraint(comparator='<', version=SemverVersion(string='1.0.0')),))
+        """
+        inverted_constraints = []
+
+        if len(self.constraints) == 1 and self.constraints[0].comparator == "*":
+            # The inverse of "*" is an empty range.
+            return None
+
+        for constraint in self.constraints:
+            if constraint.comparator in INVERTED_COMPARATORS:
+                inverted_comparator = INVERTED_COMPARATORS[constraint.comparator]
+            else:
+                raise NotImplementedError(
+                    f"Cannot invert a range with a {constraint.comparator!r} comparator."
+                )
+            inverted_constraint = VersionConstraint(
+                comparator=inverted_comparator,
+                version=constraint.version,
+            )
+            inverted_constraints.append(inverted_constraint)
+        return self.__class__(constraints=inverted_constraints)
+
     def __str__(self):
         constraints = "|".join(str(c) for c in sorted(self.constraints))
         return f"vers:{self.scheme}/{constraints}"