# Implementation Plan: Scoreboard — Distinct Line Colors per Top-10 Player on Score Graph

## Status

**Feature NOT yet implemented.** The `PLAYER_COLOR_PALETTE` exposes 10 distinct
hex colors and there are 10 legend entries / 10 polylines, but each `colorIndex`
is derived from `stablePlayerColorIndex(playerId)` — an FNV-1a hash modulo 10.
For many player-id sets (including the reported one) that hash produces
collisions: e.g. `PlayerC` and `Player05` both hash to `5` → `#ec4899`;
`Player07` and `Player08` both hash to `9` → `#84cc16`; `PlayerA` and
`Player10` both hash to `2` → `#10b981`. Verified empirically:

```
hash → palette index
PlayerA  → 2  (#10b981) green
PlayerB  → 8  (#6366f1)
PlayerC  → 5  (#ec4899) pink    ← collides with Player05
Player04 → 8  (#6366f1)
Player05 → 5  (#ec4899) pink    ← collides with PlayerC
Player06 → 3  (#ef4444)
Player07 → 9  (#84cc16) lime    ← collides with Player08
Player08 → 9  (#84cc16) lime    ← collides with Player07
Player09 → 3  (#ef4444)
Player10 → 2  (#10b981) green   ← collides with PlayerA
```

Collisions are observed across **all four** scoreboard tabs (Ranking swatch,
Matrix first-column swatch, Event Log has no swatch, Score Graph swatch +
polyline) because every component reads its color through the same
`colorIndex → PLAYER_COLOR_PALETTE` lookup.

The Job text limits the symptom to the Score Graph, but the root cause is
shared data (`colorIndex`), so the fix must be applied at the data layer
(`scoreboard.pure.ts`) and re-projected through `scoreboard.store.ts` so the
same top-10 player keeps the same distinct color in every tab.

## 1. Architectural Reconnaissance

- **Framework & language:** TypeScript strict mode, Angular standalone
  components, NestJS backend (irrelevant for this fix — the bug is purely
  client-side rendering).
- **Code style:** Standalone components with `ChangeDetectionStrategy.OnPush`,
  signal-based store, pure-function helpers in `scoreboard.pure.ts` (no
  Angular DI), services in `*.service.ts`, store in `*.store.ts`.
- **Data layer:** Pure-function projections over server-supplied payloads.
  The four tabs are populated from
  `/api/v1/scoreboard/{ranking,matrix,event-log,graph}` (parallel fetch in
  `ScoreboardStore.loadAll()`) and incrementally patched in
  `ScoreboardStore.applySolveEvent()` from the `/api/v1/events` SSE
  `solve` frame.
- **Color model:** A single readonly 10-entry hex array
  `PLAYER_COLOR_PALETTE` in `frontend/src/app/features/scoreboard/scoreboard.pure.ts:73`
  and a hashing helper `stablePlayerColorIndex(playerId)`
  (`scoreboard.pure.ts:86`). Every consumer (ranking, matrix, score-graph)
  reads `PLAYER_COLOR_PALETTE[idx]` directly. There is currently **no**
  collision-resolution pass.
- **Test framework & structure:** Jest 29 with `ts-jest` preset, configured
  by `/repo/tests/jest.config.js` (two projects: `backend` and `frontend`,
  the latter with `jsdom`). Tests live exclusively in `/repo/tests/frontend/`
  and `/repo/tests/backend/` (never next to source). Single command:
  `npm test` from the repo root.
- **Required tools & dependencies:** None new. The fix is purely a
  pure-function rewrite inside existing files plus a tiny test addition.
  No `setup.sh` change, no new packages.

## 2. Impacted Files

- **To Modify:**
  - `frontend/src/app/features/scoreboard/scoreboard.pure.ts` — add a
    collision-free top-N palette assigner; rewire the three projection
    helpers (`parseSolveEventIntoRanking`, `mutateMatrixFromSolve`,
    `applySolveToGraph`) so they use it instead of bare
    `stablePlayerColorIndex`.
  - `frontend/src/app/features/scoreboard/scoreboard.store.ts` — apply
    the unique-color projection after `loadAll()` populates each signal
    (ranking/matrix/graph) so the initial REST responses also benefit.
  - `tests/frontend/scoreboard.pure.spec.ts` — add focused specs covering
    the new collision-free assigner (success path: distinct indices for
    the documented colliding ID set) and a regression spec asserting
    existing single-player behaviour still holds.

- **To Create:** None.

## 3. Proposed Changes

### 3.1. Add a unique-color assigner in `scoreboard.pure.ts`

Export a new pure helper next to `stablePlayerColorIndex`:

```ts
export function assignUniquePlayerColors<T extends { playerId: string }>(
  items: readonly T[],
  getColorIndex: (t: T) => number,
  capacity: number = PLAYER_COLOR_PALETTE.length,
): T[] {
  const used = new Set<number>();
  const out: T[] = [];
  for (const item of items) {
    const preferred = ((getColorIndex(item) % capacity) + capacity) % capacity;
    let chosen = preferred;
    if (used.has(preferred)) {
      // Linear probe — the top-10 window guarantees a free slot exists.
      let probe = (preferred + 1) % capacity;
      while (used.has(probe) && probe !== preferred) {
        probe = (probe + 1) % capacity;
      }
      chosen = probe;
    }
    used.add(chosen);
    out.push({ ...item, colorIndex: chosen } as T);
  }
  return out;
}
```

Semantics:

- The first player keeps their hashed index; collisions are pushed to the
  next free slot via linear probe. With `capacity = 10` and at most 10
  players, a free slot is always found (the input length is itself
  bounded to ≤ capacity by the upstream `top-10 cutoff` in
  `applySolveToGraph`).
- Order is preserved → ranking/rank-cell order is unaffected.
- The mapper is injected so the same helper works for `RankingRow`,
  `GraphSeries`, and any future list type that needs a `colorIndex`.

### 3.2. Use the assigner inside the three projection helpers

In `parseSolveEventIntoRanking`, replace the direct assignment at the
"new player" branch (currently
`colorIndex: stablePlayerColorIndex(payload.playerId)`) by:

1. Build a temporary list of the affected/new player with the hashed index.
2. After the sort, call `assignUniquePlayerColors(sorted, (r) => r.colorIndex)`
   and return that.

In `mutateMatrixFromSolve`, when a brand-new player is appended, derive
their provisional `colorIndex` from the hash, then post-process the
`players` array with `assignUniquePlayerColors` before returning.

In `applySolveToGraph`, after the new series is added and the array is
sorted + sliced to top 10, run `assignUniquePlayerColors` on the top-10
series so the polyline colors are guaranteed unique. New players appended
after the cutoff don't affect the top-10.

This keeps the FNV hash as the **deterministic preference** (so a
player retains their color across all tabs and across reloads whenever
possible) while guaranteeing uniqueness inside the top-10 window.

### 3.3. Apply the same pass after `loadAll()` in `scoreboard.store.ts`

The initial REST responses already arrive with `colorIndex` set by the
backend (which uses the same hashing convention). After the four
parallel fetches resolve, re-project each view through the new assigner
so the very first paint also shows distinct colors. Specifically, in
the success branch of `loadAll()`:

```ts
this._ranking.set(assignUniquePlayerColors(ranking, (r) => r.colorIndex));
const matrixPlayers = assignUniquePlayerColors(matrix.players, (p) => p.colorIndex);
this._matrix.set({ ...matrix, players: matrixPlayers });
this._graph.set({ ...graph, series: assignUniquePlayerColors(graph.series, (s) => s.colorIndex) });
```

(Backed by tests in §4; the projection is a no-op when there is only
one player or when no collisions exist.)

### 3.4. Verify Ranking/Matrix tabs visually

The existing `ranking.component.ts:68`, `matrix.component.ts:108`, and
`score-graph.component.ts:112` `color(idx)` helpers already guard
against out-of-range indices via the same modulo trick the assigner
uses, so no template changes are required — they keep working as soon as
`colorIndex` is unique.

## 4. Test Strategy

- **Target test file:** `tests/frontend/scoreboard.pure.spec.ts`
  (and one regression test for `applySolveToGraph` covering the exact
  Job example: ten PlayerC/Player05-style IDs).
- **Mocking strategy:** The helper is a pure function with no DOM, no
  Angular DI, and no async — it is imported directly into the existing
  spec file, which already mocks only `@angular/common/http` (no extra
  setup needed). No `TestBed`, no fixtures, no chart rendering.
- **Spec list (minimal, focused):**
  1. `assignUniquePlayerColors` returns distinct indices for the
     documented colliding id set
     `['PlayerA','PlayerB','PlayerC','Player04','Player05','Player06','Player07','Player08','Player09','Player10']`
     and the colors they map to are all different (assert via
     `PLAYER_COLOR_PALETTE[idx]` set size === 10).
  2. `assignUniquePlayerColors` is a no-op when there are no collisions
     (single player, or hashed indices already unique).
  3. `applySolveToGraph` end-to-end: feed it an empty view + 10 SSE
     solves for 10 colliding players, then assert every series in the
     resulting `view.series` has a unique `colorIndex` (regression for
     the Job's DOM-inspection symptom at the polyline level).
  4. `parseSolveEventIntoRanking` regression: existing test still passes
     — proves the rewire did not change ranking sort/points logic.

- **How to run:** `npm test` from the repo root (resolves to the
  pre-configured Jest project; frontend project selected automatically
  because all impacted specs live under `tests/frontend/`).