scadalink-design/docs/requirements/Component-Commons.md

Component: Commons

Purpose

The Commons component provides the shared foundation of data types, interfaces, enums, message contracts, data transfer objects, and persistence-ignorant domain entity classes used across all other ScadaLink components. It ensures consistent type definitions for cross-component communication, data access, and eliminates duplication of common abstractions.

Location

Referenced by all component libraries and the Host.

Responsibilities

• Define shared data types (enums, value objects, result types) used across multiple components.
• Define persistence-ignorant domain entity classes (POCOs) representing all configuration database entities. These classes have no dependency on Entity Framework or any persistence framework — EF mapping is handled entirely by the Configuration Database component via Fluent API.
• Define per-component repository interfaces that consuming components use for data access. Repository implementations are owned by the Configuration Database component.
• Define protocol abstraction interfaces for the Data Connection Layer.
• Define cross-component message contracts and DTOs for deployment, health, communication, instance lifecycle, and other inter-component data flows.
• Contain no business logic — only data structures, interfaces, and enums.
• Maintain minimal dependencies — only core .NET libraries; no Akka.NET, no ASP.NET, no Entity Framework.

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Requirements

REQ-COM-1: Shared Data Type System

Commons must define shared primitive and utility types used across multiple components, including but not limited to:

• DataType enum: Enumerates the data types supported by the system (e.g., Boolean, Int32, Float, Double, String, DateTime, Binary).
• RetryPolicy: A record or immutable class describing retry behavior (max retries, fixed delay between retries).
• Result<T>: A discriminated result type that represents either a success value or an error, enabling consistent error handling across component boundaries without exceptions.
• InstanceState enum: Enabled, Disabled.
• DeploymentStatus enum: Pending, InProgress, Success, Failed.
• AlarmState enum: Active, Normal.
• AlarmLevel enum: None, Low, LowLow, High, HighHigh. Severity level for an active alarm; always None for binary trigger types, set by HiLo triggers.
• AlarmTriggerType enum: ValueMatch, RangeViolation, RateOfChange, HiLo.
• ConnectionHealth enum: Connected, Disconnected, Connecting, Error.
• TrackedOperationId: A GUID identifying a tracked store-and-forward operation (ExternalSystem.CachedCall, Database.CachedWrite, Notify.Send). Generated caller-side at the site at call time, returned to the script as a tracking handle, and reused as the idempotency key for telemetry sent to central. The notification domain's existing NotificationId is the notification-specific name for this same concept.
• TrackedOperationKind enum: ExternalCall, DatabaseWrite. Discriminates the two cached-call kinds carried by a tracked operation (notifications are tracked separately via the NotificationType enum).
• TrackedOperationStatus enum: Pending, Retrying, Delivered, Parked, Failed, Discarded. The unified lifecycle state shared by all tracked store-and-forward operations. This is the operation's externally-observable lifecycle status in the site-local tracking table (the status record); it is related to but distinct from the S&F buffer's own StoreAndForwardMessageStatus, which tracks a buffered message's retry state within the buffer (the retry mechanism). Failed (permanent failure) has no notification analogue — notifications use only the other five states (the NotificationStatus enum omits Failed).
• AuditChannel enum: ApiOutbound, DbOutbound, Notification, ApiInbound. Discriminates the script-trust-boundary channel that produced an AuditEvent. Owned by the Audit Log component.
• AuditKind enum: SyncCall, CachedEnqueued, CachedAttempt, CachedTerminal, SyncWrite, SyncRead, Enqueued, Attempt, Terminal, Completed. Channel-specific event kind — the valid Kind values for each AuditChannel are listed in the Audit Log component design (Component-AuditLog.md).
• AuditStatus enum: Success, TransientFailure, PermanentFailure, Enqueued, Retrying, Delivered, Parked, Discarded. Outcome of a single audit event row; superset of TrackedOperationStatus to also cover one-shot sync calls.
• AuditEvent: A record carrying every column of the central AuditLog row — EventId (GUID, idempotency key), OccurredAtUtc, IngestedAtUtc, Channel (AuditChannel), Kind (AuditKind), CorrelationId, SourceSiteId, SourceInstanceId, SourceScript, Actor, Target, Status (AuditStatus), HttpStatus, DurationMs, ErrorMessage, ErrorDetail, RequestSummary, ResponseSummary, PayloadTruncated, Extra — plus a site-only ForwardState (Pending | Forwarded | Reconciled) used by the site SQLite write-buffer's telemetry/reconciliation loop. IngestedAtUtc is unset at the site and stamped on central ingest. See Component-AuditLog.md for the persistence schema and ingest semantics.

Types defined here must be immutable and thread-safe.

Timestamp convention: All timestamps throughout the system must use UTC (DateTime with DateTimeKind.Utc or DateTimeOffset with zero offset). This applies to all stored timestamps (SQLite, MS SQL, audit log entries), all message timestamps (attribute values, alarm state changes, health reports, event log entries, deployment records), and all wire-format timestamps (Akka remoting, Inbound API responses). Local time conversion, if needed, is a UI display concern only.

REQ-COM-2: Protocol Abstraction

Commons must define the protocol abstraction interfaces that the Data Connection Layer implements and other components consume:

• IDataConnection: The common interface for reading, writing, and subscribing to device data regardless of the underlying protocol (OPC UA, custom legacy, etc.).
• Related types: Tag identifiers, read/write results, subscription callbacks, connection status enums, and quality codes.

These interfaces must not reference any specific protocol implementation.

REQ-COM-3: Domain Entity Classes (POCOs)

Commons must define persistence-ignorant POCO entity classes for all configuration database entities. These classes:

• Are plain C# classes with properties — no EF attributes, no base classes from EF, no navigation property annotations.
• May include navigation properties (e.g., Template.Attributes as ICollection<TemplateAttribute>) defined as plain collections. The Configuration Database component configures the relationships via Fluent API.
• May include constructors that enforce invariants (e.g., required fields).
• Must have no dependency on Entity Framework Core or any persistence library.

Entity classes are organized by domain area:

• Template & Modeling: Template, TemplateAttribute, TemplateAlarm, TemplateScript, TemplateComposition, TemplateFolder.
• Instances: Instance, InstanceAttributeOverride, InstanceConnectionBinding, InstanceAlarmOverride, Area.
• Shared Scripts: SharedScript.
• Sites & Data Connections: Site, DataConnection.
• External Systems & Database Connections: ExternalSystemDefinition, ExternalSystemMethod, DatabaseConnectionDefinition.
• Notifications: NotificationList (carries a Type field — NotificationType enum — selecting the list's notification type and its type-specific targets), NotificationRecipient, SmtpConfiguration, Notification (the durable central-queue row — see below).
• Inbound API: ApiKey, ApiMethod.
• Security: LdapGroupMapping, SiteScopeRule.
• Deployment: DeploymentRecord, SystemArtifactDeploymentRecord, DeployedConfigSnapshot.
• Audit: AuditLogEntry.

The Notification entity is the persistence-ignorant POCO for a row of the central Notifications table — the durable notification queue owned by the Notification Outbox. It is a plain class with properties for NotificationId (GUID, the idempotency key), Type (NotificationType enum discriminator), ListName, Subject, Body, TypeData (a JSON string — the type-agnostic extensibility hook), Status (NotificationStatus enum), RetryCount, LastError, ResolvedTargets, the provenance fields SourceSiteId / SourceInstanceId / SourceScript, and the UTC timestamps SiteEnqueuedAt, CreatedAt, LastAttemptAt, NextAttemptAt, DeliveredAt. As with every entity class it has no EF dependency; the Configuration Database component supplies the Fluent API mapping, value conversions, and indexes. The Type and Status enums (NotificationType: Email, Teams, …; NotificationStatus: Pending, Retrying, Delivered, Parked, Discarded) are defined under Types/Enums/ per REQ-COM-1.

REQ-COM-4: Per-Component Repository Interfaces

Commons must define repository interfaces that consuming components use for data access. Each interface is tailored to the data needs of its consuming component:

• ITemplateEngineRepository — Templates, attributes, alarms, scripts, compositions, template folders, instances, overrides, alarm overrides, connection bindings, areas.
• IDeploymentManagerRepository — Deployment records, deployed configuration snapshots, system-wide artifact deployment records.
• ISecurityRepository — LDAP group mappings, site scoping rules.
• IInboundApiRepository — API keys, API method definitions.
• IExternalSystemRepository — External system definitions, method definitions, database connection definitions.
• INotificationRepository — Notification lists (including the Type field), recipients, SMTP configuration.
• INotificationOutboxRepository — The Notifications table: insert-if-not-exists ingest on NotificationId, due-row polling (Pending rows and Retrying rows past NextAttemptAt), status transitions, KPI aggregate queries, and the bulk delete of terminal rows used by the daily purge job.
• ISiteCallAuditRepository — The SiteCalls table: insert-if-not-exists ingest on TrackedOperationId, upsert-on-newer-status from telemetry and reconciliation pulls, KPI aggregate queries, and the bulk delete of terminal rows used by the daily purge job.
• ISiteRepository — Sites, data connections, and their site assignments.
• ICentralUiRepository — Read-oriented queries spanning multiple domain areas for display purposes.

All repository interfaces must:

• Accept and return the POCO entity classes defined in Commons.
• Include a SaveChangesAsync() method (or equivalent) to support unit-of-work commit.
• Have no dependency on Entity Framework Core — they are pure interfaces.

Implementations of these interfaces are owned by the Configuration Database component.

REQ-COM-4a: Cross-Cutting Service Interfaces

Commons must define service interfaces for cross-cutting concerns that multiple components consume:

• IAuditService: Provides a single method for components to log audit entries: LogAsync(user, action, entityType, entityId, entityName, afterState). The implementation (owned by the Configuration Database component) serializes the state as JSON and adds the audit entry to the current unit-of-work transaction. Defined in Commons so any central component can call it without depending on the Configuration Database component directly.
• IDatabaseGateway: Provides script-facing ADO.NET database access via named database connections. Implemented by the External System Gateway, consumed by the Site Runtime's script runtime context.
• IExternalSystemClient: Provides script-facing invocation of external system HTTP APIs (synchronous Call and store-and-forward CachedCall). Implemented by the External System Gateway, consumed by the script runtime context.
• IInstanceLocator: Resolves an instance unique name to its site identifier. Used by the Inbound API's Route.To() to determine the destination site.
• INotificationDeliveryService: Sends notifications to a named notification list, routing transient failures to store-and-forward. Implemented by the Notification Service, consumed by the script runtime context.
• IAuditWriter: Site-local hot-path interface for appending an AuditEvent to the site SQLite AuditLog: Task WriteAsync(AuditEvent evt, CancellationToken ct). Single durable INSERT, ForwardState = Pending. Consumed by the script-trust-boundary call paths (External System Gateway, Database layer, Store-and-Forward Engine). Implementation lives in the Audit Log component.
• ICentralAuditWriter: Central direct-write interface for central-originated audit rows (Inbound API request completion, Notification Outbox dispatcher attempts/terminals): Task WriteAsync(AuditEvent evt, CancellationToken ct), with insert-if-not-exists semantics on EventId so retried handlers cannot produce duplicates. Implementation lives in the Audit Log component.

These interfaces are defined in Commons so that consuming components depend only on the abstraction, not on the implementing component.

REQ-COM-5: Cross-Component Message Contracts

Commons must define the shared DTOs and message contracts used for inter-component communication, including:

• Deployment DTOs: Configuration snapshots, deployment commands, deployment status, validation results.
• Instance Lifecycle DTOs: Disable, enable, delete commands and responses.
• Health DTOs: Health check results, site status reports, heartbeat messages. Includes script error rates and alarm evaluation error rates.
• Communication DTOs: Site identity, connection state, routing metadata.
• Attribute Stream DTOs: Attribute value change messages (instance name, attribute path, value, quality, timestamp) and alarm state change messages (instance name, alarm name, state, priority, timestamp) for the site-wide Akka stream.
• Debug View DTOs: Subscribe/unsubscribe requests, one-shot snapshot request (DebugSnapshotRequest), initial snapshot, stream filter criteria.
• Script Execution DTOs: Script call requests (with recursion depth), return values, error results.
• System-Wide Artifact DTOs: Shared script packages, external system definitions, database connection definitions, notification list definitions.
• Notification DTOs: NotificationSubmit (site→central submission: NotificationId, ListName, Subject, Body, provenance, SiteEnqueuedAt) and NotificationSubmitAck (central acknowledgement returned only after the Notifications row is persisted — ack-after-persist — which the site Store-and-Forward Engine waits on before clearing the buffered message). NotificationStatusQuery / NotificationStatusResponse back the Notify.Status script API, round-tripping a status record (status, retry count, last error, key timestamps) once a notification has been forwarded. Recipient resolution is not part of any contract — the site forwards only (listName, subject, body) and central resolves the list at delivery time. Subject to the additive-only evolution rules in REQ-COM-5a, since a submission can cross the site→central version-skew boundary.
• Cached Call Tracking DTOs: CachedCallTelemetry (site→central lifecycle telemetry for a tracked cached call: TrackedOperationId, source site, Kind — the TrackedOperationKind enum (ExternalCall / DatabaseWrite) — target summary, status, retry count, last error, key timestamps, and source instance / script provenance) and CachedCallReconcileRequest / CachedCallReconcileResponse (cursor-based per-site pull of tracking rows changed since a cursor, used so missed telemetry self-heals). All three live in the Integration/ message folder and are subject to the additive-only evolution rules in REQ-COM-5a, since they cross the site→central version-skew boundary. CachedCallTelemetry is additively extended to also carry the AuditEvent content for the corresponding lifecycle transition (CachedEnqueued / CachedAttempt / CachedTerminal), so one packet drives both the SiteCalls operational upsert and the AuditLog insert-if-not-exists in a single central transaction — see Component-AuditLog.md, Cached Operations — Combined Telemetry.
• Parked Operation Command DTOs: RetryParkedOperation and DiscardParkedOperation (central→site command/control messages keyed by TrackedOperationId, instructing the owning site to retry or discard a parked store-and-forward operation). These generalize the existing parked-message retry/discard commands to also cover parked cached calls; they live in the RemoteQuery/ message folder alongside the other parked-message management messages.
• Audit Telemetry DTOs: AuditTelemetryEnvelope (site→central gRPC message wrapping a batch of AuditEvent rows for the IngestAuditEvents telemetry call) and the matching reconciliation pull messages (PullAuditEvents request/response carrying a sinceUtc cursor and a batch of AuditEvent rows). Live in the Integration/ message folder, subject to the additive-only evolution rules in REQ-COM-5a since they cross the site→central version-skew boundary. Cached-operation audit rows do not travel via AuditTelemetryEnvelope — they are folded into CachedCallTelemetry per the bullet above.

All message types must be record types or immutable classes suitable for use as Akka.NET messages (though Commons itself must not depend on Akka.NET).

REQ-COM-5a: Message Contract Versioning

Since the system supports cross-site artifact version skew (sites may temporarily run different versions), message contracts must follow additive-only evolution rules:

• New fields may be added with default values. Existing fields must not be removed or have their types changed.
• Serialization must tolerate unknown fields (forward compatibility) and missing optional fields (backward compatibility).
• Breaking changes require a new message type and a coordinated deployment to all nodes.
• The Akka.NET serialization binding configuration (in the Host component) must explicitly map message types to serializers to prevent accidental binary serialization.

REQ-COM-5b: Namespace & Folder Convention

All types in Commons are organized by category and domain area using a consistent namespace and folder hierarchy:

ScadaLink.Commons/
├── Types/                          # REQ-COM-1: Shared data types
│   ├── Result.cs
│   ├── RetryPolicy.cs
│   ├── ScriptArgs.cs               # script-call parameter normalization helper
│   ├── ScriptParameters.cs         # typed script-parameter access helper
│   ├── StaleTagMonitor.cs          # heartbeat staleness watchdog
│   ├── ValueFormatter.cs           # culture-invariant value-to-string helper
│   ├── DynamicJsonElement.cs       # dynamic JSON wrapper for scripts
│   ├── TrackedOperationId.cs       # tracked store-and-forward operation ID (GUID)
│   ├── Enums/                      # InstanceState, DeploymentStatus, AlarmState,
│   │                               #   AlarmLevel, AlarmTriggerType, ConnectionHealth,
│   │                               #   DataType, StoreAndForwardCategory,
│   │                               #   StoreAndForwardMessageStatus,
│   │                               #   NotificationType, NotificationStatus,
│   │                               #   TrackedOperationKind, TrackedOperationStatus,
│   │                               #   AuditChannel, AuditKind, AuditStatus
│   ├── Audit/                      # AuditEvent record (site + central audit row)
│   ├── DataConnections/            # OPC UA endpoint config value objects + enums
│   ├── Flattening/                 # FlattenedConfiguration, ConfigurationDiff,
│   │                               #   DeploymentPackage, ValidationResult
│   └── Scripts/                    # AlarmContext, ScriptScope
├── Interfaces/                     # Shared interfaces by concern
│   ├── Protocol/                   # REQ-COM-2: Protocol abstraction (IDataConnection, etc.)
│   ├── Repositories/               # REQ-COM-4: Per-component repository interfaces
│   │   ├── ITemplateEngineRepository.cs
│   │   ├── IDeploymentManagerRepository.cs
│   │   ├── ISecurityRepository.cs
│   │   ├── IInboundApiRepository.cs
│   │   ├── IExternalSystemRepository.cs
│   │   ├── INotificationRepository.cs
│   │   ├── INotificationOutboxRepository.cs
│   │   ├── ISiteCallAuditRepository.cs
│   │   ├── ISiteRepository.cs
│   │   └── ICentralUiRepository.cs
│   └── Services/                   # REQ-COM-4a: Cross-cutting service interfaces
│       ├── IAuditService.cs
│       ├── IAuditWriter.cs
│       ├── ICentralAuditWriter.cs
│       ├── IDatabaseGateway.cs
│       ├── IExternalSystemClient.cs
│       ├── IInstanceLocator.cs
│       └── INotificationDeliveryService.cs
├── Entities/                       # REQ-COM-3: Domain entity POCOs, by domain area
│   ├── Templates/                  # Template, TemplateAttribute, TemplateAlarm,
│   │                               #   TemplateScript, TemplateComposition, TemplateFolder
│   ├── Instances/                  # Instance, InstanceAttributeOverride,
│   │                               #   InstanceConnectionBinding, InstanceAlarmOverride, Area
│   ├── Sites/                      # Site, DataConnection
│   ├── ExternalSystems/            # ExternalSystemDefinition, ExternalSystemMethod,
│   │                               #   DatabaseConnectionDefinition
│   ├── Notifications/              # NotificationList, NotificationRecipient, SmtpConfiguration,
│   │                               #   Notification (central Notifications-table row)
│   ├── InboundApi/                 # ApiKey, ApiMethod
│   ├── Security/                   # LdapGroupMapping, SiteScopeRule
│   ├── Deployment/                 # DeploymentRecord, SystemArtifactDeploymentRecord,
│   │                               #   DeployedConfigSnapshot
│   ├── Scripts/                    # SharedScript
│   └── Audit/                      # AuditLogEntry
├── Messages/                       # REQ-COM-5: Cross-component message contracts, by concern
│   ├── Deployment/
│   ├── Lifecycle/
│   ├── Health/
│   ├── Communication/
│   ├── Streaming/
│   ├── DebugView/
│   ├── ScriptExecution/
│   ├── Artifacts/
│   ├── DataConnection/             # data-connection subscribe/write/health messages
│   ├── Instance/                   # attribute get/set request/command messages
│   ├── Integration/                # external-integration call request/response,
│   │                               #   cached-call tracking telemetry + reconcile,
│   │                               #   audit telemetry envelope + reconcile
│   ├── Notification/               # NotificationSubmit + ack,
│   │                               #   NotificationStatusQuery/Response
│   ├── InboundApi/                 # Route.To() request messages
│   ├── RemoteQuery/                # event-log and parked-message query messages,
│   │                               #   parked-operation retry/discard commands
│   └── Management/                 # HTTP/ClusterClient management commands + registry
├── Serialization/                  # OpcUaEndpointConfigSerializer (typed↔legacy JSON)
└── Validators/                     # OpcUaEndpointConfigValidator

Naming rules:

• Namespaces mirror the folder structure: ScadaLink.Commons.Entities.Templates, ScadaLink.Commons.Interfaces.Repositories, etc.
• Interface names use the I prefix: ITemplateEngineRepository, IAuditService, IDataConnection.
• Entity classes are named after the domain concept (no suffixes like Entity or Model): Template, Instance, Site.
• Message contracts are named as commands, events, or responses: DeployInstanceCommand, DeploymentStatusResponse, AttributeValueChanged.
• Enums use singular names: AlarmState, not AlarmStates.

REQ-COM-6: No Business Logic; Pure Helpers Permitted

Commons must contain only:

• Data structures (records, classes, structs)
• Interfaces
• Enums
• Constants
• Pure, stateless helpers — see the carve-out below.

It must not contain any business logic that orchestrates other components, service implementations that perform I/O (database, network, file system), actor definitions, or orchestration code.

Pure-helper carve-out. Commons may contain stateless, side-effect-free helper types whose behavior is confined to transforming, formatting, parsing, or validating the data types Commons already defines, provided they:

• have no dependency on Akka.NET, ASP.NET Core, EF Core, or any I/O surface (consistent with REQ-COM-7);
• hold no shared mutable state across calls (a self-contained instance helper such as StaleTagMonitor, which owns only its own timer, is acceptable);
• do not call into other components or perform orchestration.

Examples currently in Commons that fall under this carve-out: Result<T>, ScriptParameters and ScriptArgs (script-parameter shaping), ValueFormatter (value-to-string formatting), DynamicJsonElement (dynamic JSON access), StaleTagMonitor (a self-contained heartbeat watchdog), OpcUaEndpointConfigSerializer (typed↔legacy JSON conversion of a Commons value object) and OpcUaEndpointConfigValidator (rule checks over a Commons value object). These are intentionally placed in Commons so every consuming component shares one implementation rather than duplicating the logic. Anything that would require an I/O dependency, mutable cross-call state, or knowledge of another component's behavior does not qualify and must live in the owning component.

REQ-COM-7: Minimal Dependencies

Commons must depend only on core .NET libraries (System.*, Microsoft.Extensions.Primitives if needed). It must not reference:

• Akka.NET or any Akka.* packages
• ASP.NET Core or any Microsoft.AspNetCore.* packages
• Entity Framework Core or any Microsoft.EntityFrameworkCore.* packages
• Any third-party libraries requiring paid licenses

This ensures Commons can be referenced by all components without introducing transitive dependency conflicts.

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Dependencies

• None — only core .NET SDK.

Interactions

• All component libraries: Reference Commons for shared types, interfaces, entity classes, and contracts.
• Configuration Database: Implements the repository interfaces defined in Commons. Maps the POCO entity classes to the database via EF Core Fluent API.
• Host: References Commons transitively through the component libraries.