"""
Allergy extraction engine distinguishing drug/food allergies from side effects.
"""

import re
from typing import Dict, Any, List, Optional, Union

ALLERGEN_PATTERNS = [
    (r"(penicillin)", "Penicillin"),
    (r"(sulfa)", "Sulfa drugs"),
    (r"(aspirin)", "Aspirin"),
    (r"(dust)", "Dust allergy"),
    (r"(peanuts)", "Peanuts"),
    (r"(milk|dairy)", "Milk / Dairy"),
]


def extract_allergies(
    message: str,
    normalized_msg: str,
    last_ai_message: Optional[str] = None
) -> Optional[Union[List[Dict[str, Any]], Dict[str, Any]]]:
    """
    Extracts structured allergies or confirmed_none container.
    """
    msg_lower = normalized_msg.lower()

    # Check for explicit negation of allergies
    neg_phrases = [
        "no allergies", "no allergy", "no drug allergy", "no food allergy", "not allergic",
        "nkda", "no allergic reaction", "அலர்ஜி எதுவும் இல்லை", "எந்த அலர்ஜியும் இல்லை",
        "कोई एलर्जी नहीं", "कोई समस्या नहीं", "ఏ అలర్జీ లేదు", "ಯಾವ ಅಲರ್ಜಿ ಇಲ್ಲ"
    ]
    if any(neg in msg_lower for neg in neg_phrases):
        return {"status": "confirmed_none", "items": []}

    allergies: List[Dict[str, Any]] = []
    has_allergen = any(re.search(pat, msg_lower) for pat, _ in ALLERGEN_PATTERNS)
    has_alg_indicator = any(k in msg_lower or k in message for k in ["allergic", "allergy", "அலர்ஜி", "ஒவ்வாமை", "एलर्जी", "rash", "reaction", "side effect", "தடிப்பு", "எடுத்தா"])

    # Side effect distinction: "Paracetamol didn't reduce fever" is NOT an allergy
    if "didn't reduce" in msg_lower or "didn't work" in msg_lower or "no effect" in msg_lower:
        return None

    if has_allergen or has_alg_indicator:
        for pat, allergen in ALLERGEN_PATTERNS:
            if re.search(pat, msg_lower):
                alg_obj: Dict[str, Any] = {"name": allergen}
                if "rash" in msg_lower or "தடிப்பு" in message or "खुजली" in message:
                    alg_obj["reaction"] = "Rash / Skin reaction"
                allergies.append(alg_obj)

        if not allergies and has_alg_indicator:
            allergies.append({"name": "Reported allergy", "type": "unspecified"})

    return allergies if allergies else None