# Brass & Sigil Launcher

A custom Minecraft Java Edition launcher built for distributing the private
"Brass & Sigil" modpack (Create + aeronautics + tech + magic + Distant
Horizons) to a small friend group.

> **NOT AN OFFICIAL MINECRAFT PRODUCT. NOT APPROVED BY OR ASSOCIATED WITH
> MOJANG OR MICROSOFT.**

## What it does

1. Fetches a JSON manifest from a self-hosted server and syncs the modpack
   files (mods, configs, resourcepacks) to the player's local install
   directory. SHA-1 hashing ensures only changed files are downloaded.
2. Authenticates each player with their own personal Microsoft account via
   the standard MSAL OAuth + Xbox Live + Minecraft Services chain, using the
   open-source `CmlLib.Core.Auth.Microsoft` library without modification.
3. Installs the appropriate Minecraft Java Edition version and Forge mod
   loader, then launches the game with the player's authenticated session.

## Stack

- **C# / .NET 8**
- **Avalonia 12** -- desktop UI
- **CmlLib.Core 4.x** -- Minecraft install + launch
- **CmlLib.Core.Auth.Microsoft 3.x + XboxAuthNet.Game.Msal** -- Microsoft auth
- **CmlLib.Core.Installer.Forge** -- Forge support

## Build

Requires the .NET 8 SDK.

```powershell
dotnet build
```

To produce the shippable single-file executable (~46 MB):

```powershell
dotnet publish -c Release -r win-x64 --self-contained true
```

Output: `bin/Release/net8.0/win-x64/publish/ModpackLauncher.exe` -- a single
file with no other dependencies, ready to send to a friend.

## Configuration

The repo ships with a `launcher-config.template.json`. Copy it to
`launcher-config.json` and fill in real values before building:

```powershell
Copy-Item launcher-config.template.json launcher-config.json
```

`launcher-config.json` is gitignored so local values (manifest URL, Azure
client ID) never get committed.

### Fields

| Field | Purpose |
| --- | --- |
| `packName` | Display name shown in the launcher |
| `manifestUrl` | URL of the hosted manifest JSON |
| `installDirName` | Folder name under `%APPDATA%` for game files |
| `memoryMinMB` / `memoryMaxMB` | JVM memory defaults |
| `msalClientId` | Azure App Registration client ID for Microsoft auth |

The config is **embedded into the exe** at build time, so the launcher ships
as a single self-contained file. A sidecar `launcher-config.json` placed
beside the exe will override the embedded copy at runtime (handy for testing).

## Manifest format

See `manifest.example.json` for the schema. Minimum:

```json
{
  "name": "Brass & Sigil",
  "version": "1.0.0",
  "minecraft": { "version": "1.20.1" },
  "loader": { "type": "forge", "version": "47.2.0" },
  "files": [
    { "path": "mods/example.jar", "url": "https://...", "sha1": "..." }
  ]
}
```

The launcher diffs the manifest against the local install dir using SHA-1
hashes and downloads only what has changed. Files removed from the manifest
are pruned from managed folders (`mods/`, `config/`, `resourcepacks/`,
`shaderpacks/`, `kubejs/`, `defaultconfigs/`).

## Privacy

The launcher does not collect, store, or transmit any user data beyond what
the standard Microsoft and Minecraft authentication APIs require. Auth tokens
are cached locally via the MSAL token cache. No telemetry, no analytics, no
third-party services beyond Microsoft and Mojang.

Local data is written to:

- `%APPDATA%\BrassAndSigil\` -- launcher settings + log file
- `%APPDATA%\<installDirName>\` -- modpack and Minecraft installation

## License

MIT -- see [LICENSE](LICENSE).

## Author

Matt Sijbers -- [https://sijbers.uk/matt](https://sijbers.uk/matt) /
[project page](https://sijbers.uk/brass-and-sigil)