# LoaderEvent

Six events emitted by `lighty-loaders` when the `events` feature is on. They surface through the global bus as `Event::Loader(LoaderEvent::…)`.

Defined in `crates/event/src/module/loader.rs`. Full workspace catalogue: [`../../event/docs/events.md`](/lightylauncher/crates/event/docs/events.md).

## Variants

| Variant             | Fields                                             | When                                                          |
| ------------------- | -------------------------------------------------- | ------------------------------------------------------------- |
| `FetchingData`      | `loader, minecraft_version, loader_version`        | Before HTTP fetch of a loader manifest                        |
| `DataFetched`       | `loader, minecraft_version, loader_version`        | After the manifest lands and parses                           |
| `ManifestNotFound`  | `loader, minecraft_version, loader_version, error` | Provider returned 404 or version missing                      |
| `ManifestCached`    | `loader`                                           | Repository hit the cache instead of fetching                  |
| `MergingLoaderData` | `base_loader, overlay_loader`                      | Before a Fabric / Quilt / Forge / NeoForge merge with Vanilla |
| `DataMerged`        | `base_loader, overlay_loader`                      | After the merge completes                                     |

`loader` is the human name: `"Vanilla"`, `"Fabric"`, `"Quilt"`, `"NeoForge"`, `"Forge"`, `"LightyUpdater"`.

## Typical sequences

**Cold fetch** (first time, no cache):

```
FetchingData { loader: "Fabric", ... }
DataFetched   { loader: "Fabric", ... }
MergingLoaderData { base_loader: "Vanilla", overlay_loader: "Fabric" }
DataMerged   { base_loader: "Vanilla", overlay_loader: "Fabric" }
```

**Warm** (cache hit):

```
ManifestCached { loader: "Fabric" }
```

**Partial** (Vanilla cached, Fabric not):

```
ManifestCached { loader: "Vanilla" }
FetchingData   { loader: "Fabric", ... }
DataFetched    { loader: "Fabric", ... }
MergingLoaderData ...
DataMerged ...
```

**Not found**:

```
FetchingData      { loader: "Fabric", loader_version: "0.99", ... }
ManifestNotFound  { loader: "Fabric", error: "...", ... }
```

## Subscriber

```rust
use lighty_event::{Event, EventBus, LoaderEvent};

let bus = EventBus::new(1000);
let mut rx = bus.subscribe();

tokio::spawn(async move {
    while let Ok(event) = rx.next().await {
        if let Event::Loader(le) = event {
            match le {
                LoaderEvent::FetchingData     { loader, .. } => println!("[fetch] {loader}"),
                LoaderEvent::DataFetched      { loader, .. } => println!("[ok]    {loader}"),
                LoaderEvent::ManifestNotFound { loader, error, .. } => eprintln!("[404]  {loader}: {error}"),
                LoaderEvent::ManifestCached   { loader }     => println!("[cache] {loader}"),
                LoaderEvent::MergingLoaderData { base_loader, overlay_loader } =>
                    println!("[merge] {overlay_loader} <- {base_loader}"),
                LoaderEvent::DataMerged       { base_loader, overlay_loader } =>
                    println!("[merged] {overlay_loader} <- {base_loader}"),
            }
        }
    }
});
```

## See also

* [`cache.md`](/lightylauncher/crates/loaders/docs/cache.md) — what `ManifestCached` actually means
* [`query.md`](/lightylauncher/crates/loaders/docs/query.md) — where the fetch / merge events fire from
* [`../../event/docs/events.md`](/lightylauncher/crates/event/docs/events.md) — full workspace catalogue


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