Example-TCG-Site/store/utils.py

import re
from .models import Card, CardListing, Order, OrderItem, VaultItem
from django.db.models import Min
import base64
from cryptography.fernet import Fernet
from django.conf import settings
from decimal import Decimal

def add_to_vault(buyer, card, quantity=1):
    """
    Adds a card to the buyer's vault.
    """
    vault_item, created = VaultItem.objects.get_or_create(buyer=buyer, card=card)
    if not created:
        vault_item.quantity += quantity
    else:
        vault_item.quantity = quantity
    vault_item.save()

def parse_deck_list(deck_text):
    """
    Parses a deck list string and returns a list of dictionaries with 'quantity' and 'name'.
    Format expected: "4 Lightning Bolt" or "1x Lightning Bolt"
    """
    lines = deck_text.strip().split('\n')
    parsed_cards = []
    
    for line in lines:
        line = line.strip()
        if not line:
            continue
            
        match = re.match(r'^(\d+)[xX]?\s+(.+)$', line)
        if match:
            quantity = int(match.group(1))
            name = match.group(2).strip()
            parsed_cards.append({'quantity': quantity, 'name': name})
        else:
            # Maybe just name? assume 1
            parsed_cards.append({'quantity': 1, 'name': line})
            
    return parsed_cards

def find_best_listings_for_deck(parsed_cards):
    """
    Finds cheapest listings for the parsed cards.
    Returns:
    - found_items: list of {listing, quantity_needed, total_cost, card_name}
    - missing_items: list of {name, quantity}
    """
    found_items = []
    missing_items = []
    
    for item in parsed_cards:
        name = item['name']
        qty_needed = item['quantity']
        
        # Find card (simple name match)
        cards = Card.objects.filter(name__iexact=name)
        if not cards.exists():
            # Try contains
            cards = Card.objects.filter(name__icontains=name)
            
        if not cards.exists():
            missing_items.append(item)
            continue
            
        # Find cheapest listing with stock
        # We try to fill the quantity from multiple listings if needed
        listings = CardListing.objects.filter(
            card__in=cards, 
            quantity__gt=0
        ).order_by('price')
        
        qty_remaining = qty_needed
        
        for listing in listings:
            if qty_remaining <= 0:
                break
                
            qty_to_take = min(listing.quantity, qty_remaining)
            
            found_items.append({
                'listing': listing,
                'quantity': qty_to_take,
                'card_name': listing.card.name,
                'price': listing.price,
                'total': listing.price * qty_to_take
            })
            
            qty_remaining -= qty_to_take
            
        if qty_remaining > 0:
            missing_items.append({'name': name, 'quantity': qty_remaining})
             
    return found_items, missing_items

def get_user_collection(user):
    """
    Returns a dict {card_name: quantity} of cards in user's vault.
    """
    owned = {}
    if not user.is_authenticated or not hasattr(user, 'buyer_profile'):
        return owned
        
    vault_items = VaultItem.objects.filter(buyer=user.buyer_profile).select_related('card')
    for item in vault_items:
        owned[item.card.name] = item.quantity
            
    return owned

def filter_deck_by_collection(parsed_cards, owned_cards):
    """
    Subtracts owned quantities from parsed_cards.
    Returns new list of parsed_cards.
    """
    filtered = []
    for item in parsed_cards:
        name = item['name']
        needed = item['quantity']
        # Simple name match
        owned_qty = 0
        # Try exact match first
        if name in owned_cards:
             owned_qty = owned_cards[name]
        else:
             # Try case insensitive fallback
             for key in owned_cards:
                 if key.lower() == name.lower():
                     owned_qty = owned_cards[key]
                     break
        
        remaining = needed - owned_qty
        if remaining > 0:
            filtered.append({'name': name, 'quantity': remaining})
            

    return filtered

class Encryptor:
    """
    Utility for encrypting and decrypting sensitive data using Fernet.
    Derives a key from settings.SECRET_KEY.
    """
    _cipher = None

    @classmethod
    def get_cipher(cls):
        if cls._cipher is None:
            # Derive a 32-byte key from SECRET_KEY
            # Ensure key is url-safe base64-encoded 32-byte key
            # We use hashlib to ensure we get a valid 32-byte key for Fernet, 
            # regardless of SECRET_KEY length.
            import hashlib
            key_hash = hashlib.sha256(settings.SECRET_KEY.encode('utf-8')).digest()
            key_b64 = base64.urlsafe_b64encode(key_hash)
            cls._cipher = Fernet(key_b64)
        return cls._cipher

    @classmethod
    def encrypt(cls, plaintext):
        if not plaintext:
            return None
        if isinstance(plaintext, str):
            plaintext = plaintext.encode('utf-8')
        return cls.get_cipher().encrypt(plaintext)

    @classmethod
    def decrypt(cls, ciphertext):
        if not ciphertext:
            return None
        if isinstance(ciphertext, memoryview):
            ciphertext = bytes(ciphertext)
        try:
            return cls.get_cipher().decrypt(ciphertext).decode('utf-8')
        except Exception:
            return None

def calculate_platform_fee(total_amount):
    """
    Calculates platform fee: 5% + $0.70, capped at $25.
    """
    if not total_amount:
        return Decimal('0.00')
    
    fee = (total_amount * Decimal('0.05')) + Decimal('0.70')
    return min(fee, Decimal('25.00'))