generated from john/python-template
Step 4 implementation plan
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Jim Lancaster
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## Step 4: `services/upload.py` + `worker.py`
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## Objective
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Implement the MVP upload and background processing pipeline so the system can:
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1. Save uploaded files into `UPLOAD_DIR`
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2. Create `Document` + `Job(status="queued")`
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3. Process queued jobs in a worker loop:
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- `queued -> processing`
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- invoke Step 3 transcription
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- persist `Transcript`
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- finalize as `transcribed` or `failed`
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This covers MVP Feature 1 + 2 and supports REQ-1, REQ-2, REQ-3, REQ-4, REQ-6.
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---
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## Scope
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### In scope
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- `src/transcription/services/upload.py`
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- `src/transcription/worker.py`
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- Upload persistence logic + job creation
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- Worker polling and single-job processing lifecycle
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- Tests for upload + worker behavior (deterministic, no live API)
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### Out of scope
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- UI wiring (Step 5)
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- Job/transcript pages (Step 5)
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- External queue infrastructure
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- Async DB/session architecture changes (post-MVP)
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---
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## Planned Deliverables
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### Source files
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- `src/transcription/services/upload.py`
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- `src/transcription/worker.py`
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- `src/transcription/services/__init__.py` (export updates as needed)
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### Tests
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- `tests/services/test_upload.py`
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- `tests/services/test_worker.py` *(recommended for mirror consistency)*
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---
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## Design Decisions
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1. **Upload service owns file persistence + initial DB records**
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- Save file first, then create `Document` + `Job(queued)`.
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2. **Worker owns job lifecycle transitions**
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- Transition only in worker:
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- `queued -> processing`
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- `processing -> transcribed|failed`
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3. **Worker calls Step 3 service, not provider SDK directly**
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- Use `transcribe_document_image(...)` from `services/transcription.py`.
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4. **Failure details are always persisted**
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- On failure, persist transcript row with `text=None`, `error_detail=...`.
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5. **Worker loop is stoppable**
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- Simple in-process loop with stop signal/event and poll interval.
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---
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## Task-by-Task Execution Checklist
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## Phase A — Upload service (`services/upload.py`)
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- [ ] Create `src/transcription/services/upload.py`
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- [ ] Add `UploadError` exception type
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- [ ] Add result dataclass (e.g., `UploadJobResult`) with:
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- [ ] `document_id`
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- [ ] `job_id`
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- [ ] `stored_path`
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- [ ] `original_filename`
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- [ ] Implement safe filename handling:
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- [ ] basename normalization
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- [ ] collision-safe naming (e.g., UUID prefix)
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- [ ] reject path traversal patterns
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- [ ] Implement extension validation (`.jpg/.jpeg/.png/.tif/.tiff/.pdf`)
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- [ ] Implement empty-bytes validation
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- [ ] Ensure `UPLOAD_DIR` exists (`mkdir(parents=True, exist_ok=True)`)
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- [ ] Persist file bytes to disk
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- [ ] Insert `Document` and `Job(status=queued)` in one transaction
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- [ ] Return structured `UploadJobResult`
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- [ ] Add logging for upload success/failure (no sensitive payload logging)
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---
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## Phase B — Worker core (`worker.py`)
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- [ ] Create `src/transcription/worker.py`
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- [ ] Implement `process_next_queued_job(...) -> bool`
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- [ ] fetch oldest queued job
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- [ ] return `False` if none found
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- [ ] set job to `processing` + update timestamp
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- [ ] call `transcribe_document_image(image_path=...)`
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- [ ] success path: persist transcript text, mark `transcribed`
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- [ ] failure path: persist error detail, mark `failed`
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- [ ] return `True` when a job is processed
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- [ ] Implement transcript upsert behavior (avoid duplicate unique `job_id` insert issues)
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- [ ] Add structured logs for lifecycle transitions and outcomes
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---
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## Phase C — Worker loop (`worker.py`)
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- [ ] Implement `run_worker_loop(...)`
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- [ ] accepts stop signal/event
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- [ ] configurable `poll_interval_seconds`
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- [ ] repeatedly calls `process_next_queued_job`
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- [ ] sleeps when no work
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- [ ] exits cleanly on stop request
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- [ ] Keep implementation single-process/simple for MVP assumptions
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---
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## Phase D — Service exports
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- [ ] Update `src/transcription/services/__init__.py` exports
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- [ ] include upload service symbols
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- [ ] keep transcription exports intact
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---
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## Phase E — Tests (scaffold -> fill)
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### E1 Scaffold
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- [ ] Create `tests/services/test_upload.py` with class/method skeletons + one-line docstrings
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- [ ] Create `tests/services/test_worker.py` with class/method skeletons + one-line docstrings
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- [ ] Validate scaffold collection:
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- [ ] `uv run pytest --collect-only -q`
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### E2 Fill
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#### Upload tests
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- [ ] `test_create_upload_job_writes_file_and_creates_records` (`integration`)
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- [ ] `test_create_upload_job_rejects_empty_bytes` (`unit`)
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- [ ] `test_create_upload_job_rejects_unsupported_extension` (`unit`)
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- [ ] `test_create_upload_job_uses_unique_stored_filename` (`integration`)
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- [ ] `test_create_upload_job_sets_job_status_queued` (`integration`)
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#### Worker tests
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- [ ] `test_process_next_queued_job_returns_false_when_queue_empty` (`integration`)
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- [ ] `test_process_next_queued_job_transitions_processing_to_transcribed` (`integration`)
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- [ ] `test_process_next_queued_job_persists_transcript_text_on_success` (`integration`)
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- [ ] `test_process_next_queued_job_sets_failed_and_error_detail_on_failure` (`integration`)
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- [ ] `test_process_next_queued_job_updates_existing_transcript_if_present` (`integration`)
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- [ ] `test_run_worker_loop_stops_when_stop_event_is_set` (`unit`)
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### Marker usage
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- [ ] Mark pure logic tests as `@pytest.mark.unit`
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- [ ] Mark DB/service orchestration tests as `@pytest.mark.integration`
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- [ ] Reuse existing `external` only for future live endpoint checks (not required in Step 4)
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---
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## Phase F — Verification
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- [ ] `uv run pytest --collect-only -q`
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- [ ] `uv run pytest tests/services/test_upload.py -q`
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- [ ] `uv run pytest tests/services/test_worker.py -q`
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- [ ] `uv run pytest -m "unit or integration" -q`
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- [ ] `uv run pytest -q`
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---
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## Implementation Guardrails
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- [ ] Do not couple worker directly to provider SDK internals
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- [ ] Do not swallow exceptions silently
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- [ ] Always persist terminal failure details
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- [ ] Keep status transitions explicit and timestamped
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- [ ] Keep default test suite deterministic and fast (no live network)
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---
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## Definition of Done (Step 4)
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- [ ] Upload service persists file + creates `Document` and queued `Job`
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- [ ] Worker processes queued jobs end-to-end via Step 3 service
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- [ ] Success writes transcript text and final `transcribed` status
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- [ ] Failure writes `error_detail` and final `failed` status
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- [ ] Queue-empty worker call returns cleanly without error
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- [ ] Full test suite passes with `uv run pytest -q`
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