Document adapter extension guide and service API contracts
epic-external-system-integration-configuration-core-services-task-018 — Write technical documentation covering: the adapter interface contract with implementation guide for adding a new external system adapter, the Integration Config Service public API with method signatures and error types, the FieldMappingResolver transformation pipeline, and the Validator rule extension pattern. This documentation enables future teams to add new integrations without touching core service code.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 9 - 22 tasks
Can start after Tier 8 completes
Handles integration between different epics or system components. Requires coordination across multiple development streams.
Implementation Notes
Write documentation as Markdown files co-located with the source code (e.g., docs/integrations/adapter-extension-guide.md). Use real integration names (Xledger, Dynamics, Cornerstone, Consio, Bufdir) in all examples — avoid generic 'MyAdapter' placeholders wherever possible to maximize relevance. Structure the adapter guide as: (1) Prerequisites, (2) Interface contract with annotated Dart abstract class, (3) Step-by-step implementation walkthrough, (4) Registration in the type registry, (5) Testing your adapter. For the FieldMappingResolver pipeline, a linear flow diagram (even ASCII art) aids comprehension significantly.
Ensure the Validator section demonstrates the extension pattern using a concrete example such as a Norwegian organization number (organisasjonsnummer) validator. Cross-reference all sections to actual source file paths to reduce context-switching for future developers.
Testing Requirements
No automated tests required for documentation itself. However, include a documentation validation checklist: (1) Code samples must be copy-pasteable and compile in isolation.
(2) At minimum one 'new adapter walkthrough' must be validated by a developer following the guide from scratch on a feature branch. (3) All referenced method names must be verified against the actual codebase to prevent doc drift. Suggest a CI lint step that checks for broken internal doc references.
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.