Refactor to not use regex

Signed-off-by: Samk <sampurnapyne1710@gmail.com>

Author: Samk1710

src/univers/version_range.py

@@ -790,23 +790,56 @@ def from_ossa_native(cls, string):
 
         >>> str(PypiVersionRange.from_ossa_native("<20.2.1, >=21.0.0 <21.2.1, ==22.0.0"))
         'vers:pypi/<20.2.1|>=21.0.0|<21.2.1|22.0.0'
+
+        >>> str(PypiVersionRange.from_ossa_native(">=1.15.0<1.15.2, 1.16.0"))
+        'vers:pypi/>=1.15.0|<1.15.2|1.16.0'
         """
 
         # Normalize "and" keyword to comma
         # "<=5.0.3, >=6.0.0 <=6.1.0 and ==7.0.0" -> "<=5.0.3, >=6.0.0 <=6.1.0, ==7.0.0"
         string = string.replace(" and ", ",")
 
-        # Remove spaces around operators
-        # "<=5.0.3, >=6.0.0 <=6.1.0, ==7.0.0" -> "<=5.0.3,>=6.0.0<=6.1.0,==7.0.0"
-        string = re.sub(r"\s+([<>=!]+)", r"\1", string)
-        string = re.sub(r"([<>=!]+)\s+", r"\1", string)
-
-        # Insert comma between consecutive constraints
-        # "<=5.0.3,>=6.0.0<=6.1.0,==7.0.0" -> "<=5.0.3,>=6.0.0,<=6.1.0,==7.0.0"
-        string = re.sub(r"(\d)([<>=!])", r"\1,\2", string)
+        # Split on commas then whitespace to get individual tokens
+        # "<=5.0.3 >=6.0.0 " -> ["<=5.0.3", ">=6.0.0"]
+        raw_tokens = [token for chunk in string.split(",") for token in chunk.split()]
+
+        if not raw_tokens:
+            raise InvalidVersionRange(f"Empty or invalid OSSA version string: {string!r}")
+
+        # Merge tokens where the operator and version are separated by a space
+        # ["<=", "5.0.3", ">=", "6.0.0"] -> ["<=5.0.3", ">=6.0.0"]
+        raw_iter = iter(raw_tokens)
+        fused_tokens = []
+        for current in raw_iter:
+            is_bare_operator = all(c in "<>=!" for c in current)
+            if is_bare_operator:
+                fused_tokens.append(current + next(raw_iter))
+            else:
+                fused_tokens.append(current)
+
+        # Split tokens that contain multiple concatenated constraints without separator
+        # ">=1.15.0<1.15.2" -> [">=1.15.0", "<1.15.2"]
+        parts = []
+        for token in fused_tokens:
+
+            token_len = len(token)
+            pos = 0
+            while pos < token_len and token[pos] in "<>=!":
+                pos += 1
+
+            segment_start = 0
+            while pos < token_len:
+                if token[pos] in "<>=!":
+                    parts.append(token[segment_start:pos])
+                    segment_start = pos
+                    while pos < token_len and token[pos] in "<>=!":
+                        pos += 1
+                else:
+                    pos += 1
+            parts.append(token[segment_start:])
 
         constraints = []
-        for part in string.split(","):
+        for part in parts:
 
             # Default to exact match for bare version numbers
             # "1.16.0" -> "=1.16.0"