Add documentation headers across system modules

Trenser.VehicleServiceSystem/Trenser.VehicleServiceSystem/services/PaymentManagementService.cpp

@@ -1,3 +1,12 @@
+/*
+File: PaymentManagementService.cpp
+Description: Implements the PaymentManagementService class which manages payment-related operations
+			 in the Vehicle Service Management System. Provides functionality for attaching/detaching observers,
+			 sending notifications, and issuing payment reminders based on invoice status and thresholds.
+Author: Trenser
+Date: 20-May-2026
+*/
+
 #include <stdexcept>
 #include "PaymentManagementService.h"
 #include "Invoice.h"
@@ -10,6 +19,14 @@
 
 util::Map<std::string, User*> PaymentManagementService::m_observers{};
 
+/*
+Function: attach
+Description: Attaches a user as an observer to the PaymentManagementService for receiving notifications.
+Parameters:
+	- user: Pointer to the User object to be attached.
+Returns:
+	- void
+*/
 void PaymentManagementService::attach(User* user)
 {
 	if (user)
@@ -22,6 +39,14 @@ void PaymentManagementService::attach(User* user)
 	}
 }
 
+/*
+Function: detach
+Description: Detaches a user from the observer list of the PaymentManagementService.
+Parameters:
+	- user: Pointer to the User object to be detached.
+Returns:
+	- void
+*/
 void PaymentManagementService::detach(User* user)
 {
 	if (user)
@@ -34,6 +59,18 @@ void PaymentManagementService::detach(User* user)
 	}
 }
 
+/*
+Function: sendNotification
+Description: Sends a notification to a user if they are registered as an observer.
+Parameters:
+	- user: Pointer to the User object to receive the notification.
+	- title: Title of the notification.
+	- message: Message content of the notification.
+Returns:
+	- void
+Throws:
+	- std::runtime_error if notification creation fails.
+*/
 void PaymentManagementService::sendNotification(User* user, const std::string& title, const std::string& message)
 {
 	if (user)
@@ -60,6 +97,15 @@ void PaymentManagementService::sendNotification(User* user, const std::string& t
 	}
 }
 
+/*
+Function: sendPaymentReminders
+Description: Iterates through all invoices in the datastore and sends payment reminders to customers
+			 whose invoices are pending beyond the configured threshold duration.
+Parameters:
+	- None
+Returns:
+	- void
+*/
 void PaymentManagementService::sendPaymentReminders()
 {
 	auto& invoicesMap = m_dataStore.getInvoices();