lib init

mail_intake/parsers/subject.py

@@ -0,0 +1,33 @@
+import re
+
+
+_PREFIX_RE = re.compile(r"^(re|fw|fwd)\s*:\s*", re.IGNORECASE)
+
+
+def normalize_subject(subject: str) -> str:
+    """
+    Normalize an email subject for thread-level comparison.
+
+    Operations:
+    - Strip common prefixes (Re:, Fwd:, FW:)
+    - Collapse whitespace
+    - Preserve original casing (no lowercasing)
+
+    This function is intentionally conservative.
+    """
+    if not subject:
+        return ""
+
+    normalized = subject.strip()
+
+    # Strip prefixes repeatedly (e.g., Re: Fwd: Re:)
+    while True:
+        new_value = _PREFIX_RE.sub("", normalized)
+        if new_value == normalized:
+            break
+        normalized = new_value.strip()
+
+    # Normalize whitespace
+    normalized = " ".join(normalized.split())
+
+    return normalized