# Flow F1 — Annotation Create

Cross-reference: `system-flows.md` → Flow F1.

## Sequence (verified against `Services/AnnotationService.cs`)

```mermaid
sequenceDiagram
    autonumber
    participant Caller as Detections / UI
    participant Ctrl as AnnotationsController (01)
    participant Svc as AnnotationService (01)
    participant Path as PathResolver (06)
    participant DB as PostgreSQL (06)
    participant FS as Filesystem
    participant Evt as AnnotationEventService (02)
    participant Q as annotations_queue_records (DB / 02)

    Caller->>Ctrl: POST /annotations (CreateAnnotationRequest, JWT ANN)
    Ctrl->>Svc: CreateAnnotation(request, userIdFromJwt)

    alt request.Image bytes provided
        Svc->>Svc: ComputeHash (XxHash64 over sampled bytes) -> id
        Svc->>FS: write {id}.jpg under images_dir
        Svc->>DB: SELECT media WHERE id = :id
        opt media row missing
            Svc->>DB: INSERT media (Image, MediaStatus.New, ...)
        end
    else MediaId provided
        Svc->>DB: SELECT media WHERE id = :MediaId (404 if missing)
        opt source media file exists & target image missing
            Svc->>FS: copy media.Path -> images_dir/{id}.jpg
        end
    end

    Svc->>DB: INSERT annotations
    Svc->>DB: BulkCopy detection rows
    Svc->>FS: write {id}.txt (YOLO label) under labels_dir
    Svc->>Evt: PublishAsync(AnnotationEventDto)
    Svc->>DB: SELECT system_settings (FirstOrDefault)
    alt SilentDetection != true
        Svc->>Q: FailsafeProducer.EnqueueAsync(db, id, QueueOperation.Created)
    end
    Svc-->>Ctrl: Annotation
    Ctrl-->>Caller: 201 Created (Location: /annotations/{id})
```

## Flowchart

```mermaid
flowchart TD
    start([POST /annotations]) --> auth{JWT valid + ANN claim?}
    auth -->|no| rej401([401 / 403])
    auth -->|yes| input{bytes or MediaId?}
    input -->|neither| arg([400 ArgumentException])
    input -->|bytes| hash[ComputeHash sampled XxHash64 -> id]
    input -->|MediaId| lookupMedia[SELECT media WHERE id = MediaId]
    lookupMedia -->|missing| nf404([404 KeyNotFound])
    lookupMedia -->|exists| copyImg[copy media.Path to images dir if missing]
    hash --> writeImg[write {id}.jpg]
    writeImg --> mediaRow[INSERT media if absent]
    mediaRow --> writeDb
    copyImg --> writeDb[INSERT annotations + BulkCopy detections]
    writeDb --> writeLabel[write {id}.txt YOLO label]
    writeLabel --> sse[PublishAsync SSE event]
    sse --> readSettings[SELECT system_settings]
    readSettings --> silentChk{SilentDetection?}
    silentChk -->|yes| ok([201 Created])
    silentChk -->|no| outbox[FailsafeProducer.EnqueueAsync Created]
    outbox --> ok

    writeImg -->|IOException| err500([500 via ErrorHandlingMiddleware])
    writeDb -->|DB error| err500
    writeLabel -->|IOException| err500
    outbox -->|DB error| err500
```

## Notes

- Image hashing is `XxHash64` over a **sampled** input (length prefix + head/middle/tail 1KB) for inputs > 3072 bytes. See ADR-004 in `architecture.md` for collision implications.
- The implementation is **not transactional across FS + DB + outbox**. Partial failure can leave orphan files or unsent outbox rows. Captured in `system-flows.md` → Open Behavioral Questions §4.
- `Update`, `UpdateStatus`, `DeleteAnnotation` paths do **NOT** publish SSE or enqueue outbox today. Captured in `system-flows.md` → Open Behavioral Questions §1.
- Outbox row is consumed asynchronously by Flow F4 (`FailsafeProducer`).