#!/usr/bin/env python3
"""
Email threading header utilities for Gmail API.
"""
from typing import Optional
def build_threading_headers(
message_id: Optional[str], references: Optional[str]
) -> dict[str, str]:
"""
Build email threading headers (In-Reply-To and References).
Args:
message_id: Message-ID of the email being replied to
references: Existing References header from original email
Returns:
Dictionary with 'In-Reply-To' and 'References' headers
Example:
>>> build_threading_headers("msg1", "msg0")
{'In-Reply-To': 'msg1', 'References': 'msg0 msg1'}
"""
if not message_id:
return {}
headers = {"In-Reply-To": message_id}
# Build References header (previous references + current message)
if references:
headers["References"] = f"{references} {message_id}"
else:
headers["References"] = message_id
return headers
