# boardgame-core

A state management library for board games using [Preact Signals](https://preactjs.com/guide/v10/signals/).

Build turn-based board games with reactive state, entity collections, spatial regions, and a command-driven game loop.

## Features

- **Reactive State Management**: Fine-grained reactivity powered by [@preact/signals-core](https://preactjs.com/guide/v10/signals/)
- **Type Safe**: Full TypeScript support with strict mode and generic context extension
- **Entity Collections**: Signal-backed collections for managing game pieces (cards, dice, tokens, meeples, etc.)
- **Region System**: Spatial management with multi-axis positioning, alignment, and shuffling
- **Command System**: CLI-style command parsing with schema validation, type coercion, and prompt support
- **Deterministic RNG**: Seeded pseudo-random number generator (Mulberry32) for reproducible game states

## Installation

```bash
npm install boardgame-core
```

## Writing a Game

### Defining a Game

Each game defines its own context type by extending `IGameContext`, creates a command registry, and exports helper functions:

```ts
import { IGameContext, createGameCommand, createGameContext, createCommandRegistry, registerCommand } from 'boardgame-core';

// 1. Define your game-specific state
type MyGameState = {
    score: number;
    round: number;
};

// 2. Extend IGameContext with your state
type MyGameContext = IGameContext & {
    state: MyGameState;
};

// 3. Define typed commands
const addScore = createGameCommand<MyGameContext, number>(
    'add-score <amount:number>',
    async function(cmd) {
        this.context.state.score += cmd.params[0] as number;
        return this.context.state.score;
    }
);

// 4. Create and populate a registry
const registry = createCommandRegistry<MyGameContext>();
registerCommand(registry, addScore);

// 5. Export a context factory with initial state
export function createMyGameContext() {
    return createGameContext<MyGameContext>(registry, () => ({
        state: { score: 0, round: 1 },
    }));
}

// 6. Export helper functions for your game logic
export function getScore(ctx: MyGameContext) {
    return ctx.state.score;
}
```

### Running a Game

```ts
import { createMyGameContext } from './my-game';

const game = createMyGameContext();

// Run commands through the context
const result = await game.commands.run('add-score 10');
if (result.success) {
    console.log(result.result); // 10
}

// Access game state
console.log(game.state.score); // 10
```

## Sample Games

### Tic-Tac-Toe

The simplest example. Shows the basic command loop, 2D board regions, and win detection.

See [`src/samples/tic-tac-toe.ts`](src/samples/tic-tac-toe.ts).

### Boop

A more complex game with piece types (kittens/cats), supply management, the "boop" push mechanic, and graduation rules.

// Compact cards in a hand towards the start
applyAlign(handRegion);

// Shuffle positions of all parts in a region
shuffle(handRegion, rng);
```

### Command Parsing

```ts
import { parseCommand, parseCommandSchema, validateCommand } from 'boardgame-core';

// Parse a command string
const cmd = parseCommand('move card1 hand --force -x 10');
// { name: 'move', params: ['card1', 'hand'], flags: { force: true }, options: { x: '10' } }

// Define and validate against a schema
const schema = parseCommandSchema('move <from> <to> [--force] [-x: number]');
const result = validateCommand(cmd, schema);
// { valid: true }
```

### Entity Collections

```ts
import { createEntityCollection } from 'boardgame-core';

const collection = createEntityCollection();
collection.add({ id: 'a', name: 'Item A' }, { id: 'b', name: 'Item B' });

const accessor = collection.get('a');
console.log(accessor.value); // reactive access

collection.remove('a');
```

### Random Number Generation

```ts
import { createRNG } from 'boardgame-core';

const rng = createRNG(12345);
rng.nextInt(6);       // 0-5
rng.next();           // [0, 1)
rng.next(100);        // [0, 100)
rng.setSeed(999);     // reseed
```

## API Reference

### Core

| Export | Description |
|---|---|
| `IGameContext` | Base interface for the game context (parts, regions, commands, prompts) |
| `createGameContext<TContext>(registry, initialState?)` | Create a game context instance. `initialState` can be an object or factory function for custom properties |
| `createGameCommand<TContext, TResult>(schema, handler)` | Create a typed command with access to `this.context` |

### Parts

| Export | Description |
|---|---|
| `Part` | Entity type representing a game piece |
| `entity(id, data)` | Create a reactive entity |
| `flip(part)` | Cycle to the next side |
| `flipTo(part, side)` | Set to a specific side |
| `roll(part, rng)` | Randomize side using RNG |

### Regions

| Export | Description |
|---|---|
| `RegionEntity` | Entity type for spatial grouping of parts |
| `RegionAxis` | Axis definition with min/max/align |
| `applyAlign(region)` | Compact parts according to axis alignment |
| `shuffle(region, rng)` | Randomize part positions |
| `moveToRegion(part, targetRegion, position?)` | Move a part to another region |
| `moveToRegionAll(parts, targetRegion, positions?)` | Move multiple parts to another region |
| `removeFromRegion(part)` | Remove a part from its region |

### Commands

| Export | Description |
|---|---|
| `parseCommand(input)` | Parse a command string into a `Command` object |
| `parseCommandSchema(schema)` | Parse a schema string into a `CommandSchema` |
| `validateCommand(cmd, schema)` | Validate a command against a schema |
| `parseCommandWithSchema(cmd, schema)` | Parse and validate in one step |
| `applyCommandSchema(cmd, schema)` | Apply schema validation and return validated command |
| `createCommandRegistry<TContext>()` | Create a new command registry |
| `registerCommand(registry, runner)` | Register a command runner |
| `unregisterCommand(registry, name)` | Remove a command from the registry |
| `hasCommand(registry, name)` | Check if a command exists |
| `getCommand(registry, name)` | Get a command runner by name |
| `runCommand(registry, context, input)` | Parse and run a command string |
| `runCommandParsed(registry, context, command)` | Run a pre-parsed command |
| `createCommandRunnerContext(registry, context)` | Create a command runner context |
| `CommandRunner` | Command runner type with schema and run function |
| `CommandRunnerContext` | Context available inside command handlers |
| `PromptEvent` | Event dispatched when a command prompts for input |

### Utilities

| Export | Description |
|---|---|
| `createEntityCollection<T>()` | Create a reactive entity collection |
| `createRNG(seed?)` | Create a seeded RNG instance |
| `Mulberry32RNG` | Mulberry32 PRNG class |

## Scripts

```bash
npm run build       # Build with tsup
npm run test        # Run tests in watch mode
npm run test:run    # Run tests once
npm run typecheck   # Type check with TypeScript
```

## License

MIT