"""
Finance business logic services.

This module contains service classes that encapsulate business logic
for financial operations, clearance checks, and payment processing.
"""

import logging
from datetime import date, timedelta
from decimal import Decimal
from typing import Dict, List, Optional, Tuple

from django.db import transaction
from django.utils import timezone

from finance.models import Invoice, Payment, Payer

logger = logging.getLogger(__name__)


class FinancialClearanceService:
    """Service class for financial clearance operations."""
    
    @staticmethod
    def check_clearance(patient, service_type: str = None) -> Tuple[bool, str]:
        """
        Check if patient has financial clearance for service.
        
        Args:
            patient: Patient instance
            service_type: Optional service type to check specific requirements
            
        Returns:
            Tuple[bool, str]: (is_cleared, message)
        """
        try:
            # Check for outstanding invoices
            outstanding_invoices = Invoice.objects.filter(
                patient=patient,
                status__in=['ISSUED', 'PARTIALLY_PAID', 'OVERDUE']
            )
            
            if outstanding_invoices.exists():
                total_outstanding = sum(
                    invoice.amount_due for invoice in outstanding_invoices
                )
                
                # Allow small outstanding amounts (less than 10 SAR)
                if total_outstanding > Decimal('10.00'):
                    invoice_numbers = ', '.join([
                        inv.invoice_number for inv in outstanding_invoices[:3]
                    ])
                    return False, (
                        f"Outstanding invoices must be paid. "
                        f"Total due: {total_outstanding} SAR. "
                        f"Invoices: {invoice_numbers}"
                    )
            
            # Check for overdue invoices (stricter check)
            overdue_invoices = Invoice.objects.filter(
                patient=patient,
                status='OVERDUE'
            )
            
            if overdue_invoices.exists():
                return False, "Overdue invoices must be paid before check-in"
            
            # Check if service requires pre-payment
            if service_type:
                requires_prepayment = FinancialClearanceService._check_prepayment_requirement(
                    patient, service_type
                )
                if requires_prepayment:
                    return False, f"Service '{service_type}' requires pre-payment"
            
            # Check insurance coverage if applicable
            active_payer = Payer.objects.filter(
                patient=patient,
                is_active=True,
                payer_type='INSURANCE'
            ).first()
            
            if active_payer:
                # Verify insurance is not expired
                # This would integrate with insurance verification system
                logger.info(f"Patient {patient.mrn} has active insurance: {active_payer.name}")
            
            logger.info(f"Financial clearance approved for patient {patient.mrn}")
            return True, "Financial clearance approved"
            
        except Exception as e:
            logger.error(f"Error checking financial clearance for patient {patient.mrn}: {e}")
            return False, f"Error checking financial clearance: {str(e)}"
    
    @staticmethod
    def _check_prepayment_requirement(patient, service_type: str) -> bool:
        """
        Check if service requires pre-payment.
        
        Args:
            patient: Patient instance
            service_type: Service type to check
            
        Returns:
            bool: True if pre-payment required
        """
        # Define services that require pre-payment
        prepayment_services = [
            'SURGERY',
            'PROCEDURE',
            'IMAGING_ADVANCED',
        ]
        
        # Check if service type requires pre-payment
        return service_type.upper() in prepayment_services
    
    @staticmethod
    def get_outstanding_balance(patient) -> Decimal:
        """
        Get total outstanding balance for patient.
        
        Args:
            patient: Patient instance
            
        Returns:
            Decimal: Total outstanding amount
        """
        outstanding_invoices = Invoice.objects.filter(
            patient=patient,
            status__in=['ISSUED', 'PARTIALLY_PAID', 'OVERDUE']
        )
        
        total = sum(
            invoice.amount_due for invoice in outstanding_invoices
        )
        
        return Decimal(str(total))
    
    @staticmethod
    def get_outstanding_invoices(patient) -> List[Invoice]:
        """
        Get list of outstanding invoices for patient.
        
        Args:
            patient: Patient instance
            
        Returns:
            List[Invoice]: Outstanding invoices
        """
        return list(Invoice.objects.filter(
            patient=patient,
            status__in=['ISSUED', 'PARTIALLY_PAID', 'OVERDUE']
        ).order_by('-issue_date'))
    
    @staticmethod
    @transaction.atomic
    def process_payment(
        invoice: Invoice,
        amount: Decimal,
        payment_method: str,
        processed_by,
        **kwargs
    ) -> Payment:
        """
        Process a payment for an invoice.
        
        Args:
            invoice: Invoice instance
            amount: Payment amount
            payment_method: Payment method (CASH, CARD, etc.)
            processed_by: User processing the payment
            **kwargs: Additional payment fields
            
        Returns:
            Payment: Created payment instance
        """
        # Create payment record
        payment = Payment.objects.create(
            tenant=invoice.tenant,
            invoice=invoice,
            payment_date=timezone.now(),
            amount=amount,
            method=payment_method,
            status='COMPLETED',
            processed_by=processed_by,
            **kwargs
        )
        
        logger.info(
            f"Payment processed: {payment.id} for invoice {invoice.invoice_number} "
            f"Amount: {amount}"
        )
        
        return payment
    
    @staticmethod
    def check_insurance_eligibility(patient, service_type: str = None) -> Tuple[bool, str, Optional[Payer]]:
        """
        Check if patient has active insurance coverage.
        
        Args:
            patient: Patient instance
            service_type: Optional service type to check coverage
            
        Returns:
            Tuple[bool, str, Optional[Payer]]: (has_coverage, message, payer)
        """
        active_payer = Payer.objects.filter(
            patient=patient,
            is_active=True,
            payer_type='INSURANCE'
        ).first()
        
        if not active_payer:
            return False, "No active insurance coverage", None
        
        # Check coverage percentage
        if active_payer.coverage_percentage <= 0:
            return False, f"Insurance {active_payer.name} has 0% coverage", active_payer
        
        logger.info(
            f"Patient {patient.mrn} has {active_payer.coverage_percentage}% "
            f"coverage with {active_payer.name}"
        )
        
        return True, f"Covered {active_payer.coverage_percentage}% by {active_payer.name}", active_payer


class InvoiceService:
    """Service class for invoice operations."""
    
    @staticmethod
    @transaction.atomic
    def create_invoice_from_appointment(appointment) -> Invoice:
        """
        Create an invoice from a completed appointment.
        
        Args:
            appointment: Appointment instance
            
        Returns:
            Invoice: Created invoice instance
        """
        from finance.models import InvoiceLineItem, Service
        
        # Check if invoice already exists
        existing_invoice = Invoice.objects.filter(
            appointment=appointment
        ).first()
        
        if existing_invoice:
            logger.info(f"Invoice already exists for appointment {appointment.id}")
            return existing_invoice
        
        # Get service pricing
        service = Service.objects.filter(
            clinic=appointment.clinic,
            code=appointment.service_type
        ).first()
        
        if not service:
            logger.warning(
                f"No service found for {appointment.service_type} at {appointment.clinic.name_en}"
            )
            # Use default pricing
            unit_price = Decimal('100.00')
        else:
            unit_price = service.base_price.amount
        
        # Calculate amounts
        subtotal = unit_price
        tax_rate = Decimal('0.15')  # 15% VAT
        tax = subtotal * tax_rate
        total = subtotal + tax
        
        # Create invoice
        invoice = Invoice.objects.create(
            tenant=appointment.tenant,
            patient=appointment.patient,
            appointment=appointment,
            issue_date=date.today(),
            due_date=date.today() + timedelta(days=30),
            subtotal=subtotal,
            tax=tax,
            total=total,
            status='ISSUED'
        )
        
        # Create line item
        InvoiceLineItem.objects.create(
            invoice=invoice,
            service=service,
            description=f"{appointment.service_type} - {appointment.clinic.name_en}",
            quantity=1,
            unit_price=unit_price,
            total=unit_price
        )
        
        logger.info(
            f"Invoice created: {invoice.invoice_number} for appointment {appointment.appointment_number}"
        )
        
        return invoice