@startuml
!include <C4/C4_Component>

title Component Diagram: API Backend — Timeline (Zeitstrahl)

ContainerDb(db, "PostgreSQL", "PostgreSQL 16")

System_Boundary(backend, "API Backend (Spring Boot)") {
    Component(timelineRepo, "TimelineEventRepository", "Spring Data JPA", "Reads and writes TimelineEvent rows and their persons/documents join tables (timeline_event_persons, timeline_event_documents).")

    Component(timelineSvc, "TimelineEventService", "Spring Service", "Owns curated-event CRUD: assembles TimelineEventView inside the transaction (lazy ManyToMany + open-in-view=false, ADR-036/ADR-040), populates createdBy/updatedBy from the session principal, and translates optimistic-lock conflicts to DomainException.conflict. Also exposes assembleDerivedEvents(): computes Geburt/Tod/Heirat TimelineEntryDTOs on read from Person/PersonRelationship data — never persisted (ADR-043).")
    Component(timelineCtrl, "TimelineEventController", "Spring MVC", "Exposes /api/timeline/events reads (READ_ALL) and writes (WRITE_ALL). createdBy/updatedBy are never bound from request bodies (CWE-639).")

    Component(timelineAssemblySvc, "TimelineService", "Spring Service", "Assembles GET /api/timeline response: merges curated TimelineEvent rows, derived life-events (via TimelineEventService), and archive letters (via DocumentService) into a year-bucketed TimelineDTO. Applies personId, generation, type, fromYear/toYear filters. WITHIN_BAND_ORDER: precision rank desc → date asc → title alpha → id tiebreak.")
    Component(timelineAssemblyCtrl, "TimelineController", "Spring MVC", "Exposes GET /api/timeline (READ_ALL). Five optional query params: personId, generation (@Min(0)), type (EventType enum), fromYear, toYear. @Validated on class for constraint enforcement.")
}

System_Ext(documentDomain, "Document domain", "Provides DatePrecision (shared value type), Document references for linked letters, and getAllForTimeline() bulk fetch")
System_Ext(personDomain, "Person domain", "Provides Person references (PersonService.findAllFamilyMembers, getPersonsByGeneration, getById) and SPOUSE_OF edges (RelationshipService.findAllSpouseEdges) for derived-event assembly and generation filtering")

Rel(timelineRepo, db, "SQL queries", "JDBC")
Rel(timelineSvc, timelineRepo, "Reads / writes events")
Rel(timelineCtrl, timelineSvc, "Delegates to")
Rel(timelineRepo, personDomain, "References persons via join table")
Rel(timelineRepo, documentDomain, "References documents via join table")
Rel(timelineSvc, personDomain, "findAllFamilyMembers() + findAllSpouseEdges() for derived-event assembly")
Rel(timelineAssemblyCtrl, timelineAssemblySvc, "Delegates to")
Rel(timelineAssemblySvc, timelineRepo, "findAll() for curated events")
Rel(timelineAssemblySvc, timelineSvc, "assembleDerivedEvents() for derived life-events")
Rel(timelineAssemblySvc, personDomain, "getPersonsByGeneration(), getById() for generation/personId filters")
Rel(timelineAssemblySvc, documentDomain, "getAllForTimeline(), getDocumentsBySender(), getDocumentsByReceiver() for letter layer")

@enduml
