sim/README.md

# World Simulation

A browser-based world simulation with a Rust server and a Leptos/Wasm UI. The server runs the simulation and exposes its state over HTTP and WebSockets. You can edit terrain and resources, manage people and animals, and customize agent behavior with the included Rune script.

Living simulation entities (people, rabbits, and wolves) run as Picard actors. The world coordinates terrain, shared resources, and actor messages; Rune behavior scripts remain on the simulation thread because Rune's VM is not `Send`.

The **Calendar and life-stage durations** panel configures ticks per day and the number of days, weeks, and months in larger calendar units. Each human life stage has an inclusive minimum/maximum duration in in-game days; the world samples within that range when a person enters the stage. These settings are stored with the world snapshot.

The UI is built automatically as part of `cargo run` and embedded in the server binary. There is no separate manual UI build step.

## Getting Started

### Local run with SQLite

Install Rust with `rustup`. The build script installs the `wasm32-unknown-unknown` target if it is missing. Start locally with SQLite using:

```sh
just dev
```

Open [http://127.0.0.1:7878](http://127.0.0.1:7878). The database is SQLite at `sim.db` in the current directory, and the initial seed is `42`. You can also run directly with `cargo run`.

To choose a seed on the first run:

```sh
cargo run -- 123
```

An existing database snapshot takes precedence on later runs, including over a new command-line seed. Use the UI's **Reset** button to start a fresh world with its current seed, or **Regenerate** to choose a different seed.

### Run with Just

Install [Just](https://just.systems/), then list the project recipes:

```sh
just
```

Useful recipes:

```sh
just run  # Stop Compose services, then build and start the app with Postgres
just stop # Stop Compose services; keep the database volume
just dev  # Run locally with SQLite
```

### Run with Docker Compose and Postgres

Install Docker with the Compose plugin, then run `just run`. This stops any existing Compose stack before rebuilding and starting the app with Postgres. You can also use the equivalent Docker command directly:

```sh
docker compose up --build -d
```

Open [http://localhost:7878](http://localhost:7878). Compose waits for Postgres to become healthy before starting the app. Postgres data is stored in the `postgres_data` volume and survives container restarts, `just stop`, and `docker compose down`.

To remove the database volume and all saved simulation data as well:

```sh
docker compose down -v
```

The Compose file uses development-only database credentials. Change them before exposing the service beyond a trusted local environment.

## Database Configuration

The server selects its database through `DATABASE_URL`:

| Backend          | Example URL                             |
| ---------------- | --------------------------------------- |
| SQLite (default) | `sqlite://sim.db?mode=rwc`              |
| Postgres         | `postgres://sim:sim@localhost:5432/sim` |

For example, run locally against a reachable Postgres server with:

```sh
DATABASE_URL=postgres://sim:sim@localhost:5432/sim cargo run
```

The simulation is saved as a snapshot about once per second and restored at startup. SQLite is convenient for local testing; Compose configures the app to use Postgres.

`SIM_ADDR` sets the listen address. It defaults to `127.0.0.1:7878`; containers set it to `0.0.0.0:7878`.

## Project Layout

- `src/world.rs` contains the simulation and snapshot serialization.
- `src/main.rs` runs the Axum server, simulation thread, and HTTP/WebSocket API.
- `src/storage.rs` provides SQLite and Postgres snapshot storage.
- `src/behavior.rn` is the default Rune behavior script.
- `ui/` contains the Leptos frontend, compiled to Wasm by `build.rs`.
- `Dockerfile`, `compose.yaml`, and `Justfile` provide container and developer workflows.

## Tests

Run the server tests with:

```sh
cargo test --bin sim
```