From 72ddd7b7704f2087a52c9c0552446682918c513b Mon Sep 17 00:00:00 2001
From: Filip Wandzio <contact@philw.dev>
Date: Thu, 22 Jan 2026 23:14:08 +0100
Subject: Implement basic game files download logic

Implement core clap arguments

Respect XDG_BASE_DIR

Currently library extraction is broken because it assumes every instace has it's own library folder. This should be refactored so instances share libraries

Signed-off-by: Filip Wandzio <contact@philw.dev>
---
 src/minecraft/launcher.rs | 73 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 src/minecraft/launcher.rs

(limited to 'src/minecraft/launcher.rs')

diff --git a/src/minecraft/launcher.rs b/src/minecraft/launcher.rs
new file mode 100644
index 0000000..f7e3ecc
--- /dev/null
+++ b/src/minecraft/launcher.rs
@@ -0,0 +1,73 @@
+use std::process::Command;
+
+use log::{debug, info};
+
+use crate::{config::Config, errors::McError, minecraft::manifests::Version, platform::paths};
+
+/// Build the full classpath
+fn build_classpath(config: &Config, version: &Version) -> Result<String, McError> {
+    let sep = if cfg!(windows) { ";" } else { ":" };
+    let mut entries = Vec::new();
+
+    for lib in &version.libraries {
+        if let Some(artifact) = &lib.downloads.artifact {
+            let path = paths::library_file(config, &artifact.path)?;
+            entries.push(path.to_string_lossy().to_string());
+        }
+    }
+
+    let client_jar = paths::client_jar(config, &version.id)?;
+    entries.push(client_jar.to_string_lossy().to_string());
+    Ok(entries.join(sep))
+}
+
+/// Launch Minecraft
+pub fn launch(config: &Config, version: &Version) -> Result<(), McError> {
+    let java = &config.java_path;
+    let classpath = build_classpath(config, version)?;
+    let natives_dir = paths::natives_dir(config, &version.id);
+
+    if !natives_dir.exists() {
+        return Err(McError::Runtime(format!(
+            "Natives folder does not exist: {}",
+            natives_dir.display()
+        )));
+    }
+
+    info!("Launching Minecraft {}", version.id);
+    debug!("Classpath: {}", classpath);
+    debug!("Natives: {}", natives_dir.display());
+
+    let status = Command::new(java)
+        .arg(format!("-Xmx{}M", config.max_memory_mb))
+        .arg(format!("-Djava.library.path={}", natives_dir.display()))
+        .arg("-cp")
+        .arg(classpath)
+        .arg(&version.main_class)
+        .arg("--username")
+        .arg(&config.username)
+        .arg("--version")
+        .arg(&version.id)
+        .arg("--gameDir")
+        .arg(paths::minecraft_root(config))
+        .arg("--assetsDir")
+        .arg(paths::minecraft_root(config).join("assets"))
+        .arg("--assetIndex")
+        .arg(&version.id)
+        .arg("--uuid")
+        .arg(&config.uuid)
+        .arg("--userProperties")
+        .arg("{}")
+        .arg("--accessToken")
+        .arg("0")
+        .arg("--userType")
+        .arg("legacy")
+        .args(&config.jvm_args)
+        .status()?;
+
+    if !status.success() {
+        return Err(McError::Process("Minecraft exited with error".into()));
+    }
+
+    Ok(())
+}
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