shopdb-flask/docs/PLUGIN-LAB-PRINTEDPARTS.md

Plugin lab: build the printedparts plugin

A hand-held, build-along tutorial: construct the 3D-printed-parts storefront + kiosk plugin specified in docs/proposals/printedparts-plugin.md, stage by stage, seeing each piece work before moving on. Written for someone building their first plugin. The finished implementation lives on the feat/printedparts-plugin branch with one commit per stage, tagged lab-stage-01 .. lab-stage-10 - when stuck, git diff lab-stage-03 lab-stage-04 shows exactly what a stage changes.

Know before you start

• You are building a BUNDLED plugin inside this repo. Plugin frontend files live in core (frontend/src/...), and three core files get small edits: frontend/src/api/index.js, the sidebar icon map in AppLayout.vue, and PLUGIN_TABLE_OWNERS in shopdb/plugins/alembic_template.py. Normal for all bundled plugins - external-plugin UI packaging does not exist yet.
• Three deliberate divergences from the scaffold, each a teaching point: (1) NO AssetType - these are quantity consumables, not ADR-001 assets (stage 1); (2) the migration is a REAL baseline that creates tables, not a stamp-only anchor (stage 2); (3) the kiosk take endpoint is the product's first UNauthenticated write - read the decision record in the proposal before stage 7.
• Ground rules: import core ONLY via shopdb.api (+ shopdb.plugins.base); DB names lowercase concatenated (quantityonhand); run bash scripts/check-naming-and-style.sh + the tests at every stage; one git commit per stage.

Prerequisites: working dev environment (README quick start), skim PLUGIN-QUICKSTART.md, PLUGIN-GUIDE.md (the measuringtools exemplar this lab imitates), PLUGIN-HOOKS.md, and CONTRIBUTING.md naming rules.

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Stage 0 - orientation (no code)

Read the proposal. Tour the two reference plugins you will imitate: plugins/usb/ (checkout ledger + badge contract) and plugins/measuringtools/ (post-cutover migration baseline, hooks). See it work: run the app, log in.

Stage 1 - scaffold, minus the AssetType

flask plugin new printedparts --description "3D-printed parts inventory + kiosk checkout"

Walk the generated tree. Then diverge:

1. In plugins/printedparts/plugin.py, DELETE _ensure_asset_type and its on_install call - a printed part is a kind-with-a-count, not an asset. Replace it with settings seeding (see the tagged commit): three Setting rows, category printedparts - printedparts_code_prefix (3DP), printedparts_default_threshold (5), printedparts_unknown_badge (deny).
2. manifest.json: "dependencies": ["employees"] (badge names), "core_version": ">=0.11.0,<1.0.0", "default_enabled": false, "display_name": "3D Printed Parts".

See it work: flask plugin list shows printedparts [Available]. Commit: printedparts stage 1: scaffold, no AssetType, manifest per spec

Stage 2 - models + real migration baseline + tables live

1. Replace the scaffold model with models/printeditem.py: PrintedItem (itemcode unique+indexed, itemname, itemdescription, imageurl, quantityonhand, lowstockthreshold, binlocation, printnotes) and PrintedItemTransaction (printeditemid FK CASCADE, transactiontype take/restock/adjust, SIGNED quantitychange, employeesso, employeename, reason, transactiondate) - both on BaseModel. The ledger is the source of truth; quantityonhand is a cache moved in the same commit.
2. Update models/__init__.py exports and plugin.py get_models.
3. Register in PLUGIN_TABLE_OWNERS (shopdb/plugins/alembic_template.py): 'printedparts': ('printeditems', 'printeditemtransactions'),
4. migrations/: copy script.py.mako + the 3-line env.py from measuringtools (change PLUGIN_NAME), then hand-write versions/0001_printedparts_baseline.py with explicit op.create_table for both tables + the three transaction indexes.
5. The scaffold's api/routes.py still imports the model you deleted - make the blueprint import cleanly (a placeholder route is fine for now).

See it work:

flask plugin install printedparts && flask plugin enable printedparts
mysql> SHOW TABLES LIKE 'printed%';                    -- both tables
mysql> SELECT * FROM alembic_version_printedparts;     -- printedparts0001baseline
flask plugin upgrade-all                               -- printedparts: ok (idempotent)

Common errors (both hit for real while building this):

• An empty Migration error: on install. Root cause: anything that makes plugins.printedparts.models fail to import - the alembic env imports the models package, which pulls in plugin.py and routes.py. Here it was the scaffold routes importing the deleted model; the ImportError gets caught and retried down a subprocess path with no stderr. Fix the import, not the migration.
• KeyError: 'printedparts' from tests/test_plugin_migrations.py: add EXPECTED_HEAD_REVISION['printedparts'] = 'printedparts0001baseline' - the guard makes every new plugin declare its expected head on purpose.

Commit + tag lab-stage-02.

Stage 3 - read API + list page (the first visible win)

1. Real api/routes.py: GET /items (jwt-optional; pagination via get_pagination_params/paginate_query, search across code/name/description/bin, ?lowstock=true filter) and GET /items/<id> returning the item + its 25 most recent transactions.
2. get_navigation_items on the plugin: {'name': '3D Parts', 'icon': 'box', 'route': '/printedparts', 'position': 46}.
3. Frontend: paste the printedpartsApi client into frontend/src/api/index.js (list/get for now, paths under /printedparts/items); rename the scaffold views to PrintedItemsList/PrintedItemDetail/PrintedItemForm.vue and repoint router/routes/printedparts.js; build the list page from PrintersList.vue (global styles, useListQuery, PaginationBar) with an image thumb column and a red/green quantity badge vs the threshold.
4. Seed two or three rows by hand (SQL or flask shell) purely to have something to look at. NOTE: hand-seeded stock has no ledger backing - the stage-9 reconcile report will flag exactly these rows, which is the check working.

See it work: navigate to /printedparts - your parts in a table, low-stock row red-badged. Everything before this moment was invisible; from here on every stage shows on screen.

Common error: nav icon missing. The sidebar maps icon NAMES to Lucide components in AppLayout.vue (iconMap); an unknown name renders nothing. Add 'box': Box to the map (and the import) or reuse an existing name.

Commit + tag lab-stage-03.

Stage 4 - catalog mutations + item photos + detail/form pages

1. POST /items mints the itemcode AFTER db.session.flush() assigns the id: <prefix>-<id:04d> with the prefix from Setting. PUT /items/<id> updates catalog fields but REFUSES quantityonhand (ledger-managed). DELETE soft-retires. All @jwt_required() (permissions come in stage 6).
2. Image trio copied from shopdb/core/api/models.py: POST/DELETE /items/<id>/image + public GET /image/<filename>, storing printeditem-<id>.<ext> in instance/printedpartsimages/, wiping prior extensions on replace, prefix-guarded delete.
3. PrintedItemDetail.vue on the unified detail skeleton (hero image, info list, transactions table); PrintedItemForm.vue create/edit + photo upload on edit; extend the api client.

See it work: add a part with a photo in the UI; thumbnail on the list, hero on the detail; PUT with quantityonhand returns the ledger-managed error.

Commit + tag lab-stage-04.

Stage 5 - the ledger: restock/adjust with badge attribution

1. services/badges.py - COPY the USB badge contract (do not import plugins.usb; cross-plugin imports fail the contract test): ^0(\d+)BZ$ PayNo wrap, all-digits SSO, name lookup via the employees plugin DirectoryEmployee (lazy import, graceful fallback), and the printedparts_unknown_badge policy - deny raises a kiosk-displayable BadgeError, allow records the SSO with an empty name.
2. _ledger_write(item, type, change, sso, name, reason) - THE invariant: append the transaction row and move the cached quantity in ONE commit. Every write path goes through it.
3. POST /items/<id>/restock {quantity, badge} and /adjust {quantitychange, reason, badge}; adjust requires a reason and refuses to drive stock below zero.
4. Detail page: Restock/Adjust modals (shared Modal.vue).
5. Tests as you go: minting, cache==ledger after a restock, the PayNo badge shape, reason-required + below-zero guards, the policy toggle, 401 for anonymous. See tests/test_plugins/test_printedparts_ledger.py.

See it work: restock from the detail page with your SSO - quantity moves AND a named transaction row appears.

Common error: in tests, mutating rows through a nested app.app_context() does not reliably stick in the sqlite test env - stock the item through the real restock endpoint instead (also more honest).

Commit + tag lab-stage-05.

Stage 6 - RBAC

1. get_permissions on the plugin: view/create/edit/delete/restock, category printedparts (seeded automatically on install/enable and by flask seed permissions).
2. Add @require_permission('printedparts.<x>') under @jwt_required() on every mutation: create/edit/delete/image = create/edit/delete; restock + adjust = restock.
3. Test with the member_headers fixture (authenticated, role-less): 403 where admin succeeds - authentication alone is not authorization.

See it work: the permissions appear in the role grid (Settings > Roles), and the member test passes.

Commit + tag lab-stage-06.

Stage 7 - the kiosk (the deliberate open write)

Read the decision record in the proposal first. The take endpoint must stay: decrement-only, badge-attributed server-side, bounded, physically rate-limited. Put the justification in the plugin README.

1. Backend, both UNdecorated: GET /kiosk/item/<itemcode> (summary for a scanned bin code) and POST /kiosk/take {itemcode, badge, quantity} - validate active item, 1 <= qty <= onhand, resolve the badge, then _ledger_write(..., 'take', -quantity, ...). Error strings are shown verbatim on the kiosk - write them for a person standing at a screen.
2. TouchKeypad.vue - net-new, dumb 3x4 grid emitting digit/clear/backspace.
3. PartsKiosk.vue + a top-level /parts-kiosk route registered beside /shopfloor in router/index.js (NO requiresAuth, outside AppLayout, meta.plugin so a disabled plugin dead-ends). Three steps - scan item, scan badge, keypad quantity - driven by ONE hidden always-focused input that consumes keyboard-wedge scans (scanners type the code + Enter) for whichever step is active; manual type-in fallbacks for damaged labels. Success screen auto-resets after a few seconds.
4. Kiosk test: open access, over-take guard, unknown-badge 422, and cache==ledger afterward.

See it work: full walkthrough in a browser - type a code, badge in, keypad 2, TAKE - stock drops with your name in the ledger.

Common error (by design): the full suite fails with test_authz.py::test_mutation_rejects_roleless_member[printedparts.kiosk_take]. That sweep asserts EVERY mutating route rejects a role-less user - the framework's net against accidentally-open writes. Your kiosk take is open on purpose, so add printedparts.kiosk_take to EXEMPT_ENDPOINTS with a comment pointing at the decision record. The net stays; the exception is explicit and reviewable.

Commit + tag lab-stage-07.

Stage 8 - 1in x 0.5in bin labels

1. frontend/src/views/print/PrintedPartsLabels.vue + a public /print/printedparts-labels route beside /print/usb-labels (a plugin OWNS its label page - the USB precedent; parts are not in the asset-label TYPE_CONFIG because they are not assets).
2. The label: CODE128 of the itemcode via JsBarcode ({format:'CODE128', displayValue:false, width:1.4, height:26, margin:0})
   • the code text at ~6.5pt. A QR at 0.4in is at the edge of scanner tolerance; CODE128 of 3DP-0042 is comfortable.
3. Roll stock = one label per page: a global (unscoped) print style with @page { size: 1in 0.5in; margin: 0 } and page-break-after: always on each .bin-label. Multi-select + per-item copies; ?item=<id> preselects (the Detail page's Bin Label button).

See it work: print preview shows one 1x0.5 label per page; scan the printed barcode (or the on-screen one with a phone scanner app) into the kiosk - label -> scan -> badge -> take -> ledger is the demo moment.

Commit + tag lab-stage-08.

Stage 9 - reports + the reconcile check

1. Three jwt-optional endpoints in the plugin blueprint, each honoring ?format=csv (local CSV helper - generate_csv is not on the contract surface): /reports/stock, /reports/consumption?days=N, /reports/by-person?days=N.
2. The stock report's ledgerdelta column = cached quantityonhand minus the ledger SUM per item. Always 0 for ledger-driven stock; nonzero flags a write path that bypassed _ledger_write - your stage-3 hand-seeded rows show up here, proving the check works.
3. get_reports on the plugin (endpoint-style entries, categories inventory/usage) - they merge into GET /api/reports and the /reports hub while the plugin is enabled.

Common error: MySQL SUM() returns Decimal; int() it or the JSON carries strings.

Deferred by decision: get_dashboard_widgets (predates the ADR-010 data-only renderers; needs a core component) and a Settings card (needs a settings page to link). Reports are the monitoring surface.

Commit + tag lab-stage-09.

Stage 10 - closeout

1. Lifecycle: flask plugin disable printedparts - nav, reports, and grantable permissions disappear; API routes only disappear after a RESTART (blueprints register at startup - the guide's section 12 gotcha). Re-enable.
2. Fresh-database proof: scratch DATABASE_URL, flask db upgrade + flask plugin install/enable printedparts + upgrade-all - green with zero manual SQL.
3. Full suite: backend pytest, vitest, frontend build, naming hook.
4. Walk PLUGIN-GUIDE.md section 12's End checklist.

Done means: a colleague can clone the repo, enable the plugin, print a bin label, and take a part at the kiosk with their badge - without asking you anything.

Stage 11 (extension) - low-stock email alerts

Per-item thresholds already exist; alerting on them is a worked example of a CONTRACT ADDITION, because the mailer was not on the plugin surface:

1. Export send_email/send_alert from shopdb/api/__init__.py, bump __contract_version__ 0.11.0 -> 0.12.0, and update PLUGIN-HOOKS.md - the docs-drift guard test fails until the doc's version example matches. Manifest pins core_version >=0.12.0 since the plugin now needs it.
2. Fire the alert inside _ledger_write when a DECREMENT crosses the threshold (before > threshold >= after). Crossing, not being-below, is the natural debounce: one alert per depletion, restocking above rearms. Best-effort try/except AFTER the commit - mail failure must never fail the take.
3. Recipients: Setting printedparts_alert_email (comma-separated), empty falls back to the site's alert_recipients via send_alert. Seed the new setting in on_enable too (idempotent) so already-installed sites get it.
4. Test with a monkeypatched sender: no alert above threshold, one on the crossing, no re-fire while below, rearm after restock (see test_lowstock_alert_fires_on_crossing_only).

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Where each pattern lives (cheat sheet)

Need	Copy from
Standalone (non-asset) plugin shape	plugins/knowledgebase/
Checkout/ledger + badge contract	plugins/usb/ (api/routes.py badge regex, api/selfhosted.py name resolve)
Real-baseline plugin migration	plugins/measuringtools/migrations/
Blueprint style, pagination, authz	plugins/measuringtools/api/routes.py
Image upload/serve/delete	shopdb/core/api/models.py
Open kiosk endpoints precedent	plugins/employees/api/routes.py, plugins/notifications/api/routes.py
Plugin-owned label print view	frontend/src/views/print/USBLabelBatch.vue
Barcode/QR rendering	JsBarcode usage in AssetLabel.vue, qrLogo.js
Kiosk route posture	/shopfloor in frontend/src/router/index.js
List/Detail master templates	PrintersList.vue, PrinterDetail.vue
Reports hook + CSV	plugins/warranty/ + shopdb/core/api/reports.py
Permissions declaration	plugins/usb/plugin.py::get_permissions
The finished plugin itself	branch feat/printedparts-plugin, tags lab-stage-01..10