Define REST API Adapter interface contract
epic-external-system-integration-configuration-core-services-task-005 — Define the uniform adapter interface that all five external system REST adapters must implement. Interface includes: authenticate(), testConnection(), exportPayload(), fetchRemoteSchema(), and getCapabilities(). Implement the AdapterRegistry class with registration and lookup by integration type key. Ensures open/closed principle for adding future adapters.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Handles integration between different epics or system components. Requires coordination across multiple development streams.
Implementation Notes
Define RestApiAdapter as an abstract class rather than a Dart abstract interface (pre-Dart 3) or use `interface class` if targeting Dart 3+. Each method should have detailed dartdoc comments explaining expected behavior, error conditions, and what exceptions are permissible to throw. For AdapterRegistry, back it with a simple Map
The open/closed principle is the key architectural goal: adding a sixth adapter (e.g., a future SAP integration) should require only creating a new class implementing RestApiAdapter and calling registry.register('sap', SapAdapter()) — no changes to existing code. Document this pattern explicitly in the class dartdoc.
Testing Requirements
Unit tests using flutter_test. Create a MockAdapter that implements RestApiAdapter with configurable return values. Tests: (1) MockAdapter satisfies interface contract — all five methods callable, (2) AdapterRegistry.register() succeeds for new key, (3) AdapterRegistry.register() throws DuplicateAdapterException for duplicate key, (4) AdapterRegistry.lookup() returns correct adapter for registered key, (5) AdapterRegistry.lookup() returns null for unregistered key, (6) AdapterRegistry.lookupOrThrow() throws UnregisteredAdapterException for unregistered key, (7) getCapabilities() on MockAdapter returns synchronously without await. All tests synchronous except where Future return values are verified with await.
Each of the five external systems (Xledger, Dynamics, Cornerstone, Consio, Bufdir) has a different authentication flow, field schema, and error format. Forcing them into a uniform adapter interface may require compromises that result in leaky abstractions or make the adapter contract too complex to maintain.
Mitigation & Contingency
Mitigation: Design the IntegrationAdapter interface with a loose invoke() payload rather than a typed one, allowing each adapter to declare its own input/output schema. Use integration type metadata in the registry to document per-adapter quirks. Build Xledger first as the most documented API, then adapt the interface based on learnings.
Contingency: If the uniform interface cannot accommodate all five systems, split into two interface tiers: a simple polling/export adapter and a richer bidirectional adapter, with the registry declaring which tier each system implements.
Development and testing of the Cornerstone and Consio adapters depends on NHF providing sandbox API access. If credentials or documentation are delayed, these adapters cannot be validated, blocking the epic's acceptance criteria.
Mitigation & Contingency
Mitigation: Implement Xledger and Dynamics adapters first (better-documented, sandbox available). Create a mock adapter for Cornerstone/Consio using recorded API responses for CI testing. Proactively request sandbox access from NHF at project kickoff.
Contingency: Ship the epic with Cornerstone/Consio adapters in a 'stub' state (connectivity test returns a simulated success, invoke() is not production-wired) and gate the NHF integration behind a feature flag until real API access is obtained.
Real-world field mappings may include nested transformations, conditional logic, and data type coercions (e.g., Norwegian date formats, currency rounding rules) that the Field Mapping Resolver's initial design does not accommodate, requiring scope expansion mid-epic.
Mitigation & Contingency
Mitigation: Gather actual field mapping examples from Blindeforbundet (Xledger) and HLF (Dynamics) before designing the resolver. Identify the most complex transformation required and ensure the resolver design handles it. Limit Phase 1 to direct field renaming and format conversion only.
Contingency: If complex transformations are required, implement a simple expression evaluator (e.g., JSONata or a custom mini-DSL) as an extension point in the resolver, delivering basic mappings first and complex ones in a follow-up task.