ersatztv/docs/spa-conventions.md

SPA conventions — "Add a screen" playbook

Purpose: a precise playbook for adding a new screen (or sub-path editor) to the ChicoryTV React SPA (web/), for an agent with no prior context in this repo. Update this doc in the same PR that changes any convention below.

Companion to api-conventions.md (the API surface the SPA talks to) and docs/contributing.md (general repo conventions).

1. Stack & layout

Vite + React + TypeScript, builds to ErsatzTV/wwwroot/app (see web/vite.config.ts: base: '/app/', build.outDir: '../ErsatzTV/wwwroot/app'), served by the ASP.NET host at /app.

• Routes + nav: web/src/App.tsx — one big route table of ScreenRoute objects (path, label, title, kicker, icon, etc.) plus an allowSubPaths?: boolean flag.
• Screens: web/src/screens/*.tsx, one file per top-level screen, generally with a colocated *.test.tsx.
• API clients: web/src/api/<domain>.ts (see §4).
• Styling: web/src/shell.css (+ web/src/components/components.css) — utility classes with a ctv- prefix (~690 occurrences across those two files). Reuse an existing ctv-* class before inventing a new one.

2. CRITICAL: sub-path screens must own their own pathname state

If a route sets allowSubPaths: true (e.g. so /app/blocks/{id} works under the /app/blocks nav entry), the screen component itself must track window.location.pathname and listen for popstate — do not rely on App.tsx re-rendering ScreenContent when the sub-path changes.

Why: App.tsx's routeFromLocation() matches an allowSubPaths route by prefix (pathname.startsWith(\${route.path}/`)) and returns the **same ScreenRouteobject reference** for the base path and every sub-path under it.App's state update is setActiveRoute(routeFromLocation()); React's useStatesetter bails viaObject.iswhen the new value is reference-equal to the old one — so navigating from/app/blocksto/app/blocks/42(or between/app/blocks/42and/app/blocks/17) **never re-invokes ScreenContent** at the Applevel. See the comment block directly abovePlayoutsRouteScreeninApp.tsx (~line 3540) for the canonical explanation, and its implementation (useState(() => window.location.pathname)+useEffectwith apopstate` listener local to the wrapper component) for the fix.

Exemplars of screens that already do this correctly: BlocksScreen.tsx, TemplatesScreen.tsx, DecosScreen.tsx, DecoTemplatesScreen.tsx, and the PlayoutsRouteScreen wrapper in App.tsx (which owns two sibling sub-paths, /playouts/{id}/alternate-schedules and /playouts/{id}/templates, dispatching internally via parsePlayoutSubRoute).

Exception — a guarded sub-path route defers pathname ownership to App. When a sub-path route's screens ALSO register a dirty guard (§8), the wrapper must not self-listen for popstate; App owns the pathname and passes the approved sub-path down as a prop. The LibrariesRouteScreen wrapper in App.tsx is the exemplar (sub-path parsed by parseLibrariesSubRoute, dispatched via a flat switch, sub-path supplied by App's librariesSubPath state). See §8 for why child-before-parent effect order makes the self-listening pattern unsafe here.

3. Data loading pattern

Reference implementation: web/src/screens/LogsScreen.tsx. Structure to copy for any screen that fetches from the API:

• A discriminated-union state type covering loading/success/error, e.g. type LogsState = { status: 'loading'; ... } | { status: 'success'; ... } | { status: 'error'; ... }.
• A seqRef (monotonically incremented request counter) + activeRef (mount-tracking boolean, flipped in a mount/unmount useEffect) pair — guards against a stale, slower request overwriting a newer one's result, and against setting state after unmount.
• The actual fetch lives in a useCallback (load), called from a separate useEffect(() => { load(); }, [load]).
• Lint rule — react-hooks "no set-state-in-effect": never call setState synchronously in the body of a useEffect. State transitions happen only inside event handlers or promise .then()/.catch() callbacks (as in LogsScreen's load). This is enforced by eslint-plugin-react-hooks in web/eslint.config.js — a synchronous setState in an effect body will fail npm run lint.

3a. "Keep results visible during refetch" ⇒ gate mutations + show a refreshing cue

Some grid screens deliberately keep the previous successful result set rendered while a refetch is in flight (no full-screen loading state on a query/kind/page change), so the grid doesn't flash empty. SearchScreen.tsx and MediaBrowseScreen.tsx do this. If such a screen also carries mutation surfaces (per-card Add-to menu, Select/select-mode, a selection action bar, "Add all", "Save as smart collection"), those surfaces would otherwise stay live over a stale result set — an add/select action then targets the about-to-be-replaced items, or (worse) a query-wide "Add all" bulk request resolves against the previous query. This was issue #221 (adversarial-reviewer#18).

Convention — when a screen keeps stale results visible during a refetch:

• Key the success state to the request params that produced it. Store the identifying params on the status: 'success' variant (SearchScreen: the query; MediaBrowseScreen: a kind|query|page key), set in the seq-guarded .then. Derive const refreshing = state.status === 'success' && state.<key> !== <current params>; in render. Prefer this over a synchronously-set refreshing flag: setting state synchronously from the load path trips the react-hooks "no set-state-in-effect" rule (§3). Invariant, not a guarantee: the derivation is only self-correcting when every value the current params can take will actually trigger a fetch. If load() early-returns for some param value (e.g. SearchScreen's blank-query guard), state never updates for that value and a stale status: 'success' variant lingers — so the comparison must exclude params that suppress fetching, or gate the whole flag on the same condition that gates the fetch (SearchScreen: const refreshing = hasQuery && state.status === 'success' && state.query !== query.trim(); — fixed post-review in #222 after the naive derivation got stuck true once the query was cleared to empty, see PR discussion for #221).
• While refreshing: show a visible cue (a role="status" "Refreshing…" row with <Spinner> plus the .ctv-media-grid-dim opacity class on the grid) and disable every mutation surface — per-card Add-to menu (withhold the actions node), select toggle + in-grid selection (const canSelect = selectMode && !refreshing; gates onToggleSelect), the selection action bar, "Add all", "Save as smart collection". Card navigation (onOpen) may stay live — but only outside select mode: while selectMode && refreshing, MediaPosterCard falls back to onOpen whenever onToggleSelect is undefined, so both props must be withheld together or a mid-select click navigates away instead of no-op'ing. The select-mode toggle itself should only be disabled while refreshing when entering select mode (refreshing && !selectMode) — exiting only clears selection, not a mutation, so it must stay available.
• Bind async bulk completions to their request params, not just mount. A whole-query/whole-set request (e.g. getSearchAllItems) must, on resolve, check that its snapshotted params are still current (compare against a ref that always holds the committed value — SearchScreen reuses lastQueryRef) and discard otherwise. Checking only activeRef (mounted) is insufficient.

4. API client modules

One file per domain in web/src/api/, e.g. logs.ts, blocks.ts, playouts.ts. Pattern (see web/src/api/logs.ts):

• Re-export the generated response/DTO types from ./generated/v1: export type LogEntry = components['schemas']['LogEntryResponseModel'];
• A typed params interface for the endpoint's query string (e.g. GetLogsParams).
• The fetch function builds a URLSearchParams from only the params that are set, then calls the shared request<T>(url) helper from ./client.
• An error-message helper (e.g. messageFromLogsError) that narrows unknown → ApiError (from ./client) → a human string, with a fallback message — screens use this instead of stringifying errors themselves.
• web/src/api/index.ts re-exports everything so screens import from '../api', not from the individual domain file directly.

Trust the generated key casing — it mirrors the runtime. Since #198 the OpenAPI spec is generated to match the runtime Newtonsoft serializer exactly (a schema transformer runs the same contract resolver; see api-conventions.md §5a), so the generated types carry the real wire keys — including Newtonsoft's acronym quirks like ffmpegProfileId (channel FFmpeg-profile id) and ffmpegProfile (channel FFmpeg-profile display name). Do not hand-cast responses to "fix" a key or dual-read a spec-cased vs runtime-cased key (the old PlaybackTroubleshootingScreen #198 escape hatch that read data.channel.fFmpegProfileId has been removed — read ffmpegProfileId straight off the typed response). When you mock an API response in a test, use the generated (runtime) casing.

4a. Optimistic-concurrency editors (ETag / If-Match / 412)

Replace-all editors (Blocks is the reference; see api-conventions.md §7a for the server contract, issue #253) must round-trip the aggregate's concurrency ETag so a stale tab can't silently overwrite a fresher edit:

• Transport seam (web/src/api/client.ts): requestWithMeta<T>(path, options) returns { data, etag } (reads the ETag response header). request<T> delegates to it and drops the meta — keep using request for endpoints without a concurrency token.
• Domain module (web/src/api/blocks.ts): expose a …WithMeta load (getBlockItemsWithMeta → { data, etag }) and make the replace accept the last-seen ETag and return the new one: replaceBlock(id, body, ifMatch?) → requestWithMeta(..., { headers: ifMatch ? {'If-Match': ifMatch} : undefined }).
• Editor: hold the ETag in a useRef; set it from the load GET, and replace it from the PUT response's ETag on every successful save (a same-tab second save otherwise 412s against its own write). Keyed reload: a reloadKey state in the load useEffect dep array lets the conflict flow re-fetch.
• 412 UX: catch error instanceof ApiError && error.status === 412 on save and open a blocking "changed elsewhere — reload (unsaved changes discarded)" ConfirmDialog (Reload bumps reloadKey), distinct from a 409 ("build in progress — retry shortly"). All other errors stay the generic save-error path. Reference: web/src/screens/BlocksScreen.tsx BlockEditor.
• List-derived editors (Multi/Rerun collections open the editor from a paged-list row, not a per-record GET): fetch the single record via the …WithMeta by-id helper (getMultiCollectionWithMeta / getRerunCollectionWithMeta) when the editor mounts, and build the draft from that response — so the ETag and the draft data come from one read and stay consistent (the fail-safe ordering; don't pair a list-row draft with a separately-fetched ETag). Editors that navigate back to the list on save (Playout, Multi/Rerun, Collection reorder) need only the 412 branch — no post-save ETag rotation.

5. Artwork rendering

Render item.artwork / item.poster (or whatever the DTO field is named) directly as an <img src> — since PR #181, API responses already return rooted, directly-usable URLs (see api-conventions.md §4). Do not client-side-prefix artwork paths (no /artwork/posters/ string building in SPA code) — if you see that pattern, it's stale/wrong.

5b. HLS video preview

Screens that preview an ErsatzTV HLS stream use the reusable HlsPlayer component (web/src/media/HlsPlayer.tsx, introduced with #145). Pass it a src (the .m3u8 URL, or null for idle) and — when the manifest GET itself starts a server-side session (e.g. troubleshooting playback.m3u8) — a playToken you increment per play, so a repeat play with an identical URL still tears down and re-attaches (an unchanged src alone is a state no-op that never issues a new request); it attaches hls.js when Media Source Extensions are available and falls back to native HLS (video.canPlayType('application/vnd.apple.mpegurl'), i.e. Safari) otherwise, and tears down the hls.js instance on src change and unmount. Its config mirrors the legacy _Host.cshtml previewChannel (liveDurationInfinity: true + an unbounded manifest maxTimeToFirstByteMs) because the troubleshooting playback.m3u8 endpoint blocks until segments exist before it 302s to the live manifest. In tests, mock hls.js wholesale (vi.mock('hls.js', …) with a class exposing static isSupported(), static Events, and loadSource/attachMedia/on/destroy) so jsdom never touches a real MediaSource; assert the manifest URL via the mocked loadSource spy (see PlaybackTroubleshootingScreen.test.tsx).

5c. Media "Add to…" affordances

Screens that let the user add media items to a collection/playlist/schedule use the shared layer in web/src/media/addTo/ — AddToMenu (popover for a MediaPosterCard actions slot or a detail page's action row) and the AddToCollectionDialog / AddToPlaylistDialog / AddToScheduleDialog / SaveAsSmartCollectionDialog it drives. Do not build screen-local target pickers. Multi-select on grid screens is an explicit "Select" toggle (see docs/decisions.md 2026-07-10 for the rationale and the accepted deviations from Blazor).

5d. Client-local preferences: localStorage, namespaced ctv-* keys

Per-browser UI preferences (theme, an auth token, a screen's remembered page size) live in window.localStorage under a namespaced ctv- key, not a round-trip through the API — the established pattern is designSystem.ts's getStoredDesignSystemTheme/applyDesignSystemTheme (ctv-theme): a small getStorage() helper that returns window.localStorage wrapped in a try/catch (so a disabled/unavailable storage API degrades to the default instead of throwing), a getter that validates the stored value against the known option set before trusting it, and a setter that writes straight through. LogsScreen.tsx's page-size persistence (ctv-logs-page-size, #213) follows the same shape. Reserve this for state that's genuinely local to the browser/user session — if a preference needs to be shared across devices or is really server/business state (e.g. Blazor's ConfigElement-backed settings), it belongs behind an API endpoint instead; see docs/decisions.md 2026-07-11 for the specific reasoning on logs page-size.

5e. API key: the one keyless screen + the global 401 signal (#197)

The whole /api surface is gated behind an X-Api-Key header (server-side #197): writes always require it and reads require it too (Api:RequireKeyForReads defaults true), so a missing/wrong key yields 401 on every call. Two SPA seams support this:

• The request client sends the key on every request (web/src/api/client.ts): whenever getStoredApiKey() returns a value it's attached to X-Api-Key, regardless of method (there is no reads-vs-mutations split — that older guard was removed). The key lives in localStorage (ctv-api-key) via web/src/api/auth.ts (get/set/clearStoredApiKey), per §5d.
• The API Key screen is the one screen that must render with ZERO successful /api calls (web/src/screens/ApiKeyScreen.tsx, route /app/api-key, System nav group). A keyless first load 401s every read, so this screen reads/writes only localStorage (the auth.ts helpers) and never fetches from /api. It shows a masked "key set / no key" state (never echoes the stored key in plaintext — a type="password" input), Save (setStoredApiKey) and Clear (clearStoredApiKey), and copy pointing at the server-generated /config/api.key. If you add a keyless bootstrap screen, keep it localStorage-only for the same reason.
• 401 UX is one shell-level banner, not per-screen handling. Rather than special-casing 401 in every screen's error path, the request client emits a single app-wide signal on 401 (auth.ts notifyUnauthorized / subscribeUnauthorized), and web/src/UnauthorizedBanner.tsx (rendered once in the App shell) subscribes and points the user at /app/api-key. This is the DRY seam for "the server rejected us" — reuse it instead of adding bespoke 401 branches.

6. Tests

• vitest, colocated *.test.ts / *.test.tsx next to the source file.
• Every screen with meaningful logic gets a screen test; every API client module gets a param-mapping / URL-building test (e.g. logs.test.ts next to logs.ts).
• web/src/App.test.tsx covers navigation + the route table, including regressions like the sub-path bug in §2 (see the tests around PlayoutsRouteScreen, ~line 1682+, that click into /app/playouts/{id}/... sub-paths and assert the correct sub-screen rendered).
• Nav-label test-selector care: getByRole('link'/'button', { name: /Regex/ }) matches by substring by default — a loose regex can match more than one nav item. Verified example: the System nav button is matched with an anchored regex (name: /^System/) rather than a bare /System/, specifically to avoid ambiguous matches against other labels that start with or contain "System". Anchor (^/$) or use exact strings in getByRole name matchers whenever a new label could be a substring of (or share a substring with) an existing one — check App.tsx's nav label: list for collisions before picking a new label.
• Extracted-screen tests own their own fetch mock (Schedules #207, Channels #244): when a screen is pulled out of App.tsx into web/src/screens/<Name>Screen.tsx, its colocated <Name>Screen.test.tsx builds a self-contained vi.spyOn(window, 'fetch') mock scoped to that screen's own endpoints (plus local jsonResponse/fixture-factory helpers) and renders the screen component directly — it must not import from App.test.tsx or reuse the monolithic mockDashboardApi(). App.test.tsx keeps only a thin nav-smoke test for the extracted screen (route to it, assert it mounted and hit its own endpoint) plus genuinely cross-cutting shell concerns (route table, sub-path ownership §2, the unsaved-changes/popstate guard §8, the TopBar action wiring). Detailed screen behavior lives in the screen's own test file. See ChannelsScreen.test.tsx / SchedulesScreen.test.tsx for the shape.

7. Verification gate — run before every commit touching web/

From web/:

npm test          # vitest
npm run lint      # eslint .
npm run build     # tsc -b && vite build

Also run npm run check:api if you touched anything OpenAPI-relevant (see api-conventions.md §5) — it regenerates src/api/generated/v1.d.ts and fails the build if it's out of sync with what's committed.

8. Unsaved-changes navigation guard

Screens with a draft / explicit-Save model (edits accumulate locally, one Save flushes them — e.g. the schedules editor, web/src/screens/SchedulesScreen.tsx) must guard against losing the draft to navigation. The shared module web/src/navigationGuard.ts is the seam:

• The screen registers a guard on mount: registerNavigationGuard(() => !dirtyRef.current || window.confirm(...)), returning the unregister fn from the mount useEffect for cleanup. Only one guard is active at a time (the mounted screen); a stale unregister only clears its own guard.

• App.tsx's navigate handler calls canLeaveCurrentScreen() before pushState — a false return aborts the in-app sidebar/nav click.

• Browser Back/Forward (popstate) is also covered. App.tsx's popstate handler consults canLeaveCurrentScreen() too. A popstate cannot be cancelled — by the time it fires the URL has already changed — so on a veto the handler re-pushes the pre-pop path (tracked in a currentPathRef updated on every approved navigation) via history.pushState and leaves activeRoute untouched, effectively undoing the browser's URL change. This same handler also runs for the synthetic pop navigateToPath() dispatches, so programmatic in-app navigation is guarded as well. The re-push does not re-fire popstate; that's safe because only one screen is mounted at a time.

• Guarded sub-path routes: App owns pathname/popstate (resolves the old §2 caveat). A sub-path wrapper that BOTH tracks its own pathname (§2) AND whose sub-screens register a dirty guard cannot self-listen for popstate: React commits child passive effects before the parent, so a wrapper-owned popstate listener fires before App's guard-restore handler and would switch sub-screen before App could veto and re-push — desyncing the two. Resolution (design #202 §D.2, finding 4): App is the single popstate owner. On a pop it consults canLeaveCurrentScreen(), and only on approval does it update a currentSubPath state value (librariesSubPath) that it passes down into the wrapper; on a veto it re-pushes the pre-pop path and updates nothing, so the wrapper never sees a vetoed path. The wrapper (LibrariesRouteScreen) derives its sub-path purely from that prop — never from the raw event — so effect-commit order is irrelevant. Scope the state write to the guarded route only: the setLibrariesSubPath call is gated on the arrived route being libraries, so unguarded sub-path routes (Playouts/Media) skip it entirely and stay byte-identical (they still bail App's setActiveRoute via Object.is and self-own their pathname per §2). The regression test is the App-owned-popstate case in App.test.tsx (dirty editor at /app/libraries/local/3: confirm→false keeps URL + mounted sub-screen; confirm→true navigates). Unguarded sub-path screens (PlayoutsRouteScreen, MediaRouteScreen) keep self-owning their pathname — only screens that register a dirty guard defer to App.

• The screen also guards the paths the module still can't see — an in-screen action that would replace the draft (schedule switch, opening the properties editor) uses its own window.confirm(...), and a beforeunload listener (installed while dirty) covers full-page unloads (reload / close tab / external link).

Keep the guard predicate reading a ref (dirtyRef), not the dirty state value, so canLeaveCurrentScreen() sees the current dirtiness synchronously at click time.

9. Review checklist — temporal semantics

• For every effect / timer / async completion, ask: when does it fire (mount, dependency change, unmount, StrictMode double-invoke) and which render/request does it still own? A debounce timer fires on mount too (§3, the lastQueryRef no-change guard exists precisely for that); a .then can resolve after the params it was launched for have moved on (§3a, the refreshing gate and the Add-all query binding exist for that). A guard that only checks "still mounted" (activeRef) does not answer "still current".
• For any "make X consistent with Y" change, re-validate the exemplar Y's temporal behavior before copying it. #221 came from copying a fetch model that keeps stale results visible onto screens that had gained mutation surfaces — the exemplar was safe read-only, the copy was not. Copying a pattern copies its assumptions; confirm they still hold in the new context.