"""
Invoice generation utilities for OrderModel and ShopOrderModel.
These functions generate PDF invoices from HTML templates.
"""

from io import BytesIO
from datetime import datetime
from django.template.loader import render_to_string
from weasyprint import HTML
from django.conf import settings
import jdatetime


def generate_order_invoice(order_id):
    """
    Generate a PDF invoice for an OrderModel instance.
    
    Args:
        order_id: The ID of the OrderModel instance
    
    Returns:
        BytesIO: A BytesIO object containing the PDF data
    """
    from .models import OrderModel
    
    try:
        order = OrderModel.objects.select_related(
            'user', 'address', 'discount_code'
        ).prefetch_related('items__product__product').get(pk=order_id)
    except OrderModel.DoesNotExist:
        raise ValueError(f"Order with ID {order_id} does not exist")
    
    # Prepare items with calculated discount amounts
    items = order.items.all()
    items_with_discount = []
    for item in items:
        # Calculate the discount amount from the discount_percent
        # price is after discount, so we need to calculate original price
        # original_price = price / (1 - discount_percent/100)
        # discount_amount = original_price - price
        if item.discount_percent > 0:
            discount_multiplier = (100 - item.discount_percent) / 100
            price_after_discount = item.price
            price_before_discount = int(price_after_discount / discount_multiplier) if discount_multiplier > 0 else price_after_discount
            item_discount_amount = (price_before_discount - price_after_discount)
        else:
            item_discount_amount = 0
            price_before_discount = item.price
        
        items_with_discount.append({
            'item': item,
            'discount_amount': item_discount_amount,
            'price_before_discount': price_before_discount
        })
    
    # Prepare context for the template
    context = {
        'order': order,
        'order_number': order.pk + 1000,
        'items': items,
        'items_with_discount': items_with_discount,
        'user': order.user,
        'address': order.address,
        'discount_code': order.discount_code,
        'created_at_jalali': jdatetime.datetime.fromgregorian(datetime=order.created_at) if order.created_at else None,
        'total_items': sum(item.quantity for item in items),
        'subtotal': order.cart_total,
        'discount_amount': order.discount_amount or 0,
        'special_discount_total': order.special_discount_total or 0,
        'tax': order.tax or 0,
        'final_price': order.final_price,
        'is_paid': order.is_paid,
        'status': order.get_status_display(),
    }
    
    # Render HTML template
    html_string = render_to_string('order/invoice_order.html', context)
    
    # Generate PDF
    html = HTML(string=html_string, base_url=settings.STATIC_URL)
    pdf_file = BytesIO()
    html.write_pdf(pdf_file)
    pdf_file.seek(0)
    
    return pdf_file


def generate_shop_order_invoice(shop_order_id):
    """
    Generate a PDF invoice for a ShopOrderModel instance.
    
    Args:
        shop_order_id: The ID of the ShopOrderModel instance
    
    Returns:
        BytesIO: A BytesIO object containing the PDF data
    """
    from .models import ShopOrderModel
    
    try:
        shop_order = ShopOrderModel.objects.select_related(
            'order', 'shop', 'shop__user', 'customer', 'address'
        ).prefetch_related('items__order_item__product__product').get(pk=shop_order_id)
    except ShopOrderModel.DoesNotExist:
        raise ValueError(f"ShopOrder with ID {shop_order_id} does not exist")
    
    # Prepare context for the template
    context = {
        'shop_order': shop_order,
        'order_number': shop_order.order.pk + 1000,
        'shop_order_id': shop_order.pk,
        'shop': shop_order.shop,
        'customer': shop_order.customer,
        'customer_name': shop_order.customer_name,
        'customer_phone': shop_order.customer_phone,
        'address_text': shop_order.address_text,
        'address_postal_code': shop_order.address_postal_code,
        'address_phone': shop_order.address_phone,
        'address_city': shop_order.address_city,
        'address_province': shop_order.address_province,
        'address_recipient_name': shop_order.address_recipient_name,
        'items': shop_order.items.all(),
        'created_at_jalali': jdatetime.datetime.fromgregorian(datetime=shop_order.order_created_at) if shop_order.order_created_at else None,
        'total_items': shop_order.items_count,
        'subtotal': shop_order.subtotal,
        'discount_amount': shop_order.discount_amount,
        'special_discount_amount': shop_order.special_discount_amount,
        'tax_amount': shop_order.tax_amount,
        'commission_percent': shop_order.commission_percent,
        'commission_amount': shop_order.commission_amount,
        'payable_amount': shop_order.payable_amount,
        'is_paid': shop_order.is_paid,
        'status': shop_order.get_status_display(),
        'is_settled': shop_order.is_settled,
    }
    
    # Render HTML template
    html_string = render_to_string('order/invoice_shop_order.html', context)
    
    # Generate PDF
    html = HTML(string=html_string, base_url=settings.STATIC_URL)
    pdf_file = BytesIO()
    html.write_pdf(pdf_file)
    pdf_file.seek(0)
    
    return pdf_file