"""
Message header parsing utilities for Mail Intake.

---

## Summary

This module provides helper functions for normalizing and extracting
useful information from provider-native message headers.

The functions here are intentionally simple and tolerant of malformed
or incomplete header data.
"""

from typing import Dict, List, Tuple, Optional


def parse_headers(raw_headers: List[Dict[str, str]]) -> Dict[str, str]:
    """
    Convert a list of Gmail-style headers into a normalized dict.

    Args:
        raw_headers (List[Dict[str, str]]):
            List of header dictionaries, each containing ``name`` and ``value`` keys.

    Returns:
        Dict[str, str]:
            Dictionary mapping lowercase header names to stripped values.

    Notes:
        **Guarantees:**

            - Provider payloads (such as Gmail) typically represent headers as a list of name/value mappings
            - This function normalizes them into a case-insensitive dictionary keyed by lowercase header names

    Example:
        Typical usage:
        
            Input:
                [
                    {"name": "From", "value": "John Doe <john@example.com>"},
                    {"name": "Subject", "value": "Re: Interview Update"},
                ]
    
            Output:
                {
                    "from": "John Doe <john@example.com>",
                    "subject": "Re: Interview Update",
                }
    """
    headers: Dict[str, str] = {}

    for header in raw_headers or []:
        name = header.get("name")
        value = header.get("value")

        if not name or value is None:
            continue

        headers[name.lower()] = value.strip()

    return headers


def extract_sender(headers: Dict[str, str]) -> Tuple[str, Optional[str]]:
    """
    Extract sender email and optional display name from headers.

    Args:
        headers (Dict[str, str]):
            Normalized header dictionary as returned by :func:`parse_headers`.

    Returns:
        Tuple[str, Optional[str]]:
            A tuple ``(email, name)`` where ``email`` is the sender email address and ``name`` is the display name, or ``None`` if unavailable.

    Notes:
        **Responsibilities:**

            - This function parses the ``From`` header and attempts to extract sender email address and optional human-readable display name

    Example:
        Typical values:

            ``"John Doe <john@example.com>"`` -> ``("john@example.com", "John Doe")``
            ``"john@example.com"`` -> ``("john@example.com", None)``
    """
    from_header = headers.get("from")
    if not from_header:
        return "", None

    if "<" in from_header and ">" in from_header:
        name_part, email_part = from_header.split("<", 1)
        email = email_part.rstrip(">").strip()
        name = name_part.strip().strip('"') or None
        return email, name

    return from_header.strip(), None