Continue service layer extraction: AdapterConfigService, InventoryService, ProductService

[bokelley]

Context

PR #XXX implemented PolicyService as the first step in extracting business logic from Flask route handlers into testable service layers.

Current state:

• ✅ PolicyService handles: currencies, measurement_providers, naming_templates, approval_mode, thresholds, policies
• ❌ settings.py still directly handles: adapter config, inventory sync, product management, user management (still 1,120 lines)

Proposed Service Layer Architecture

Week 2: AdapterConfigService

Scope: "Ad Server" settings section

• Ad server selection (GAM, Kevel, Triton, Mock)
• OAuth flow and token management
• Network codes and configuration
• Connection testing
• Adapter-specific config validation

Benefits:

• Testable adapter configuration logic
• Centralized OAuth token handling
• Clear adapter validation rules

Week 3: InventoryService

Scope: "Inventory" settings section

• Sync inventory from ad server
• Ad unit and placement management
• Inventory tree operations
• GAM/Kevel/Triton inventory adapters

Benefits:

• Testable inventory sync logic
• Clear separation of inventory concerns
• Reusable across different UI patterns

Week 4: ProductService

Scope: "Products" settings section

• Product CRUD operations
• Product validation
• Implementation config management
• Property tag associations

Benefits:

• Testable product operations
• Consistent product validation
• Easier to add REST API later

Week 5: REST API Layer

Once services are extracted, add thin REST API wrappers:

• GET /api/v1/tenants/{id}/policies
• PUT /api/v1/tenants/{id}/policies
• GET /api/v1/tenants/{id}/adapter-config
• PUT /api/v1/tenants/{id}/adapter-config
• etc.

Testing Requirements

Each service should have:

• Unit tests for validation logic
• Integration tests with real database
• Clear error messages with field-specific feedback

Success Criteria

• AdapterConfigService implemented with tests
• InventoryService implemented with tests
• ProductService implemented with tests
• Route handlers refactored to use services
• settings.py reduced to ~500 lines (from 1,120)
• REST API endpoints added as thin wrappers
• All existing functionality preserved

References

• PR #XXX - PolicyService implementation (reference architecture)
• src/services/policy_service.py - Service layer pattern
• tests/unit/test_policy_service.py - Testing pattern