63 lines
1.6 KiB
Python
63 lines
1.6 KiB
Python
"""
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# Summary
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Subject line normalization utilities for Mail Intake.
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This module provides helper functions for normalizing email subject lines
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to enable reliable thread-level comparison and grouping.
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Normalization is intentionally conservative to avoid altering semantic
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meaning while removing common reply and forward prefixes.
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"""
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import re
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_PREFIX_RE = re.compile(r"^(re|fw|fwd)\s*:\s*", re.IGNORECASE)
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"""
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Regular expression matching common reply/forward subject prefixes.
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"""
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def normalize_subject(subject: str) -> str:
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"""
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Normalize an email subject for thread-level comparison.
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Args:
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subject (str):
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Raw subject line from a message header.
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Returns:
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str:
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Normalized subject string suitable for thread grouping.
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Notes:
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**Responsibilities:**
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- Strips common prefixes such as `Re:`, `Fwd:`, and `FW:`.
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- Repeats prefix stripping to handle stacked prefixes.
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- Collapses excessive whitespace.
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- Preserves original casing (no lowercasing).
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**Guarantees:**
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- This function is intentionally conservative and avoids aggressive
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transformations that could alter the semantic meaning of the subject.
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"""
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if not subject:
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return ""
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normalized = subject.strip()
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# Strip prefixes repeatedly (e.g., Re: Fwd: Re:)
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while True:
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new_value = _PREFIX_RE.sub("", normalized)
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if new_value == normalized:
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break
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normalized = new_value.strip()
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# Normalize whitespace
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normalized = " ".join(normalized.split())
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return normalized
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