# Technical structure

How this project is laid out, what each layer is allowed to do, and how to work
on it. Companion to [ARCHITECTURE.md](ARCHITECTURE.md), which states the *intent*;
this file states the *implementation*.

- Engine: **Cocos Creator 3.8.8**, TypeScript.
- Targets: Web (mobile browser), Android, iOS. Portrait only.
- Editor automation: the `cocos-code-mode` extension — see
  [CODE_MODE_SETUP.md](CODE_MODE_SETUP.md).

## Layering

Four layers, with dependencies pointing strictly downward. A layer may import
from the layers below it and never from the ones above.

```
  ui/        Cocos components: scenes, prefabs, views, input, animation
   ↓
  app/       bootstrap, service locator, scene transitions
   ↓
  modules/   engine-aware services: savegame, (later) audio, analytics
   ↓
  core/      pure rules and bots — no `cc` import anywhere
```

The rule enforced by review and by the test harness: **nothing under
`assets/scripts/core/` may import from `cc`.** It is plain TypeScript, runnable
under Node, and that is what makes the rules testable without the engine.

## Folder map

```
assets/
  scenes/
    loader.scene              module init, then → lobby
    lobby.scene               main menu; hosts the match UI
  prefabs/
    card.prefab               one playing card, face or back
    ...
  art/
    cards/                    36 faces + back, atlased
    ui/                       panels, buttons, table surface
  scripts/
    core/                     PURE TS — no engine imports
      cards/                  Suit, Rank, Card, Deck
      rules/                  GameState, actions, events, the reducer
      bot/                    PlayerView projection, Bot contract, BasicBot
      match/                  Match (stateful shell), runMatch (headless driver)
      util/                   seeded RNG, shuffle
    modules/
      save/                   SaveManager, ISaveSection, StatsSection, storage
    app/                      Bootstrap, ServiceLocator, SceneRouter
    ui/
      lobby/                  lobby screen controller
      game/                   match screen: hand, table, deck, animations
      common/                 reusable widgets, safe-area root
tests/
  core/                       vitest specs against assets/scripts/core
  support/                    position fixtures and the state invariant checker
  tools/                      measuring tools, not part of the suite
docs/                         specs, this file, plan, decisions
local/                        scratch art storage; contents get consumed
extensions/cocos-code-mode/   editor tool server
```

## The rules core

A deterministic state machine. The only entry point is a pure reducer:

```ts
apply(state: GameState, action: Action): { state: GameState; events: GameEvent[] }
```

- `GameState` is plain data: hands, deck, trump card, table slots, discard,
  phase, whose turn it is, and the RNG state. It is serialisable, which makes
  every test a fixture and every bug reproducible from a seed.
- `Action` is what a participant *wants* to do — `Attack`, `Defend`, `Take`,
  `Pass`. Legality is decided by the core, never by the caller; `legalActions()`
  exists so the UI can grey out impossible taps, not as the source of truth.
- `GameEvent` is what *happened* — `CardDealt`, `CardPlayed`, `CardBeaten`,
  `TableTaken`, `TableDiscarded`, `TurnPassed`, `PlayerOut`, `GameOver`. The view
  layer animates the event stream; it never inspects `GameState` directly for
  anything it is not allowed to see.
- Randomness comes from a seeded PRNG carried inside the state. Same seed plus
  same action sequence always reproduces the same match.

## Bots

A bot is `decide(view: PlayerView) => Action`. `PlayerView` is a projection of
`GameState` containing only legitimately visible information — own hand, table,
trump, opponents' hand *sizes*, deck and discard counts — plus the list of legal
actions. `BasicBot` implements the policy in [GAMEPLAY.md](GAMEPLAY.md).

`Match` wraps the reducer with the current state and an event subscription; the
game screen and the headless `runMatch` driver both hold one. As a reference
point, 5000 `BasicBot` self-play matches split roughly 43/43/14 between the two
seats and draws, with the opening attacker losing about 37% of the time —
`npm run stats:bot` reprints these.

## Savegame

Per [ARCHITECTURE.md](ARCHITECTURE.md): `SaveManager` keeps a registry of
`ISaveSection` implementations. `save()` enumerates them and builds
`{ [section.key]: section.save() }`; `load()` parses and dispatches each payload
back to the matching section. A missing or unparsable section is skipped with a
warning rather than failing the whole load, so a bad release cannot brick a save.

Keys are explicit string constants, not class names — release builds minify.

## Conventions

- TypeScript, 4-space indent, `PascalCase` for types, `camelCase` for members,
  `_private` for backing fields (matching Cocos's own style).
- One exported class per file, file named after it.
- Cocos components live only in `ui/`; they are thin and hold no rules logic.
- No `any` in `core/`. `strict` is off in the Cocos tsconfig for engine-side
  convenience, but the test harness type-checks `core/` in strict mode.

## Workflows

### Tests

```bash
npm test
```

Runs vitest over `tests/core` against `assets/scripts/core`. No editor required.
The soak specs play several thousand complete matches and re-check every state
invariant after every single action, so a rule regression surfaces at the move
that caused it.

```bash
npm run typecheck         # strict tsc over core/ and the tests
npm run check:core-purity # fails if core/ ever imports the engine
npm run stats:bot         # BasicBot self-play distribution, not a test
```

### Driving the editor

Cocos Creator must be running with this project open. See
[CODE_MODE_SETUP.md](CODE_MODE_SETUP.md); the port changes on every editor
restart, so always read `~/.utcp_config.json`.

Scripts and other text assets are written to disk directly and picked up by the
editor's asset watcher. Scenes and prefabs are authored through the tools —
never by hand-editing the `.scene`/`.prefab` JSON.

### Builds

Web: `web-mobile` template. Mobile: ASTC textures per [ART.md](ART.md), PNG for
web.