- Add InvoiceService with database dependency for invoice management operations
- Add GenerateMonthlyInvoice to create invoices with plan fees and usage charges from billing period
- Add SendInvoice to update invoice status to pending (email integration TODO)
- Add MarkInvoiceAsPaid to update invoice payment status
- Add GetOverdueInvoices to query invoices past due date with pending status
- Add GetSubscriber
- Add GetAccount to retrieve subscriber account information with balance and usage limits
- Add ListInvoices/GetInvoice for invoice management with line items
- Add ListRatingPlans/GetRatingPlan for rating plan queries
- Add ListAlerts/CreateAlert/ResolveAlert for alert management
- Add SearchSubscribers for subscriber search functionality
- Add SubscribeToSubscriberUpdates/SubscribeToAlertUpdates
- Move ES2 request/response types to es2_types.go
- Move profile operations (download, activate, deactivate, delete, status, list) to es2_operations.go
- Move helper methods (send requests, validation, generateRequestID) to es2_helpers.go
- Keep core ES2Service struct and ProvisionProfile in es2_client.go
- Revert sendDeactivationRequest parameter type from any back to interface{}
- Remove omitempty from Plan field in Subscriber model
- Update NotifySubscriberUpdate to use any instead of interface{}
- Update sendDeactivationRequest parameter type from interface{} to any
- Add os import for environment variable access
- Update getOperatorVariant to read OP from OPERATOR_VARIANT env var
- Add fallback to default "TelecomOP1234567" for development
- Add zero-padding for OP values shorter than 16 bytes
- Update comments to reference environment variable configuration
- Replace XOR-based OPc generation with AES-128 ECB encryption
- Add getOperatorVariant for consistent OP across subscribers
- Add AES cipher block creation with error handling
- Add OP length validation for AES-128 block size
- Update generateOPc to use crypto/aes for 3GPP-compliant OPc derivation
- Add hardcoded OP placeholder with production configuration note
- Add AMFClient and ES2Service dependencies to SubscriberService
- Initialize AMF client with default URL and ES2 service in NewSubscriberService
- Implement provisionESIMProfile with EID validation, profile provisioning, activation, and AMF notification
- Implement deactivateESIMProfile with profile deactivation, status updates, and session termination
- Add generateOPc helper for deriving OPc from OP and K using XOR-based
- Add AMFClient struct with base URL and HTTP client
- Add NewAMFClient with 30s timeout
- Add TerminateSession for subscriber session termination with reason and timestamp
- Add NotifySubscriberUpdate for subscriber status change notifications
- Add SessionTerminationRequest and SessionTerminationResponse models
- Add generateRequestID helper for request tracking
- Add ES2Service struct with HTTP client and ES2Config
- Add NewES2Service with 30s timeout and TLS configuration
- Add ProvisionProfile for eSIM profile provisioning with metadata support
- Add ActivateProfile, DeactivateProfile, and DeleteProfile for profile lifecycle management
- Add GetProfileStatus for profile state queries
- Add ListProfiles for eUICC profile enumeration
- Add ValidateEID and ValidateICCID for identifier
- Add SubscriberService struct with Database and Config dependencies
- Add NewSubscriberService constructor
- Add CreateSubscriber with IMSI allocation, auth key generation, and eSIM provisioning support
- Add GetSubscriber and GetSubscriberByIMSI for subscriber retrieval
- Add UpdateSubscriber for subscriber information updates
- Add SuspendSubscriber with session termination
- Add TerminateSubscriber with session termination and eSIM profile deactivation
- Add ListSubscribers with pagination and
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