1 files changed, 274 insertions, 0 deletions
diff --git a/src-tauri/src/core/fabric.rs b/src-tauri/src/core/fabric.rs
new file mode 100644
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+++ b/src-tauri/src/core/fabric.rs
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+//! Fabric Loader support module.
+//!
+//! This module provides functionality to:
+//! - Fetch available Fabric loader versions from the Fabric Meta API
+//! - Generate version JSON files for Fabric-enabled Minecraft versions
+//! - Install Fabric loader for a specific Minecraft version
+
+use serde::{Deserialize, Serialize};
+use std::error::Error;
+use std::path::PathBuf;
+
+const FABRIC_META_URL: &str = "https://meta.fabricmc.net/v2";
+
+/// Represents a Fabric loader version from the Meta API.
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FabricLoaderVersion {
+    pub separator: String,
+    pub build: i32,
+    pub maven: String,
+    pub version: String,
+    pub stable: bool,
+}
+
+/// Represents a Fabric intermediary mapping version.
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FabricIntermediaryVersion {
+    pub maven: String,
+    pub version: String,
+    pub stable: bool,
+}
+
+/// Represents a combined loader + intermediary version entry.
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FabricLoaderEntry {
+    pub loader: FabricLoaderVersion,
+    pub intermediary: FabricIntermediaryVersion,
+    #[serde(rename = "launcherMeta")]
+    pub launcher_meta: FabricLauncherMeta,
+}
+
+/// Launcher metadata from Fabric Meta API.
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FabricLauncherMeta {
+    pub version: i32,
+    pub libraries: FabricLibraries,
+    #[serde(rename = "mainClass")]
+    pub main_class: FabricMainClass,
+}
+
+/// Libraries required by Fabric loader.
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FabricLibraries {
+    pub client: Vec<FabricLibrary>,
+    pub common: Vec<FabricLibrary>,
+    pub server: Vec<FabricLibrary>,
+}
+
+/// A single Fabric library dependency.
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FabricLibrary {
+    pub name: String,
+    pub url: Option<String>,
+}
+
+/// Main class configuration for Fabric.
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FabricMainClass {
+    pub client: String,
+    pub server: String,
+}
+
+/// Represents a Minecraft version supported by Fabric.
+#[derive(Debug, Deserialize, Serialize, Clone)]
+pub struct FabricGameVersion {
+    pub version: String,
+    pub stable: bool,
+}
+
+/// Information about an installed Fabric version.
+#[derive(Debug, Serialize, Clone)]
+pub struct InstalledFabricVersion {
+    pub id: String,
+    pub minecraft_version: String,
+    pub loader_version: String,
+    pub path: PathBuf,
+}
+
+/// Fetch all Minecraft versions supported by Fabric.
+///
+/// # Returns
+/// A list of game versions that have Fabric intermediary mappings available.
+pub async fn fetch_supported_game_versions(
+) -> Result<Vec<FabricGameVersion>, Box<dyn Error + Send + Sync>> {
+    let url = format!("{}/versions/game", FABRIC_META_URL);
+    let resp = reqwest::get(&url)
+        .await?
+        .json::<Vec<FabricGameVersion>>()
+        .await?;
+    Ok(resp)
+}
+
+/// Fetch all available Fabric loader versions.
+///
+/// # Returns
+/// A list of all Fabric loader versions, ordered by build number (newest first).
+pub async fn fetch_loader_versions(
+) -> Result<Vec<FabricLoaderVersion>, Box<dyn Error + Send + Sync>> {
+    let url = format!("{}/versions/loader", FABRIC_META_URL);
+    let resp = reqwest::get(&url)
+        .await?
+        .json::<Vec<FabricLoaderVersion>>()
+        .await?;
+    Ok(resp)
+}
+
+/// Fetch Fabric loader versions available for a specific Minecraft version.
+///
+/// # Arguments
+/// * `game_version` - The Minecraft version (e.g., "1.20.4")
+///
+/// # Returns
+/// A list of loader entries with full metadata for the specified game version.
+pub async fn fetch_loaders_for_game_version(
+    game_version: &str,
+) -> Result<Vec<FabricLoaderEntry>, Box<dyn Error + Send + Sync>> {
+    let url = format!("{}/versions/loader/{}", FABRIC_META_URL, game_version);
+    let resp = reqwest::get(&url)
+        .await?
+        .json::<Vec<FabricLoaderEntry>>()
+        .await?;
+    Ok(resp)
+}
+
+/// Fetch the version JSON profile for a specific Fabric loader + game version combination.
+///
+/// # Arguments
+/// * `game_version` - The Minecraft version (e.g., "1.20.4")
+/// * `loader_version` - The Fabric loader version (e.g., "0.15.6")
+///
+/// # Returns
+/// The raw version JSON as a `serde_json::Value` that can be saved to the versions directory.
+pub async fn fetch_version_profile(
+    game_version: &str,
+    loader_version: &str,
+) -> Result<serde_json::Value, Box<dyn Error + Send + Sync>> {
+    let url = format!(
+        "{}/versions/loader/{}/{}/profile/json",
+        FABRIC_META_URL, game_version, loader_version
+    );
+    let resp = reqwest::get(&url)
+        .await?
+        .json::<serde_json::Value>()
+        .await?;
+    Ok(resp)
+}
+
+/// Generate the version ID for a Fabric installation.
+///
+/// # Arguments
+/// * `game_version` - The Minecraft version
+/// * `loader_version` - The Fabric loader version
+///
+/// # Returns
+/// The version ID string (e.g., "fabric-loader-0.15.6-1.20.4")
+pub fn generate_version_id(game_version: &str, loader_version: &str) -> String {
+    format!("fabric-loader-{}-{}", loader_version, game_version)
+}
+
+/// Install Fabric loader for a specific Minecraft version.
+///
+/// This creates the version JSON file in the versions directory.
+/// The actual library downloads happen during game launch.
+///
+/// # Arguments
+/// * `game_dir` - The .minecraft directory path
+/// * `game_version` - The Minecraft version (e.g., "1.20.4")
+/// * `loader_version` - The Fabric loader version (e.g., "0.15.6")
+///
+/// # Returns
+/// Information about the installed version.
+pub async fn install_fabric(
+    game_dir: &PathBuf,
+    game_version: &str,
+    loader_version: &str,
+) -> Result<InstalledFabricVersion, Box<dyn Error + Send + Sync>> {
+    // Fetch the version profile from Fabric Meta
+    let profile = fetch_version_profile(game_version, loader_version).await?;
+
+    // Get the version ID from the profile or generate it
+    let version_id = profile
+        .get("id")
+        .and_then(|v| v.as_str())
+        .map(|s| s.to_string())
+        .unwrap_or_else(|| generate_version_id(game_version, loader_version));
+
+    // Create the version directory
+    let version_dir = game_dir.join("versions").join(&version_id);
+    tokio::fs::create_dir_all(&version_dir).await?;
+
+    // Write the version JSON
+    let json_path = version_dir.join(format!("{}.json", version_id));
+    let json_content = serde_json::to_string_pretty(&profile)?;
+    tokio::fs::write(&json_path, json_content).await?;
+
+    Ok(InstalledFabricVersion {
+        id: version_id,
+        minecraft_version: game_version.to_string(),
+        loader_version: loader_version.to_string(),
+        path: json_path,
+    })
+}
+
+/// Check if Fabric is installed for a specific version combination.
+///
+/// # Arguments
+/// * `game_dir` - The .minecraft directory path
+/// * `game_version` - The Minecraft version
+/// * `loader_version` - The Fabric loader version
+///
+/// # Returns
+/// `true` if the version JSON exists, `false` otherwise.
+pub fn is_fabric_installed(game_dir: &PathBuf, game_version: &str, loader_version: &str) -> bool {
+    let version_id = generate_version_id(game_version, loader_version);
+    let json_path = game_dir
+        .join("versions")
+        .join(&version_id)
+        .join(format!("{}.json", version_id));
+    json_path.exists()
+}
+
+/// List all installed Fabric versions in the game directory.
+///
+/// # Arguments
+/// * `game_dir` - The .minecraft directory path
+///
+/// # Returns
+/// A list of installed Fabric version IDs.
+pub async fn list_installed_fabric_versions(
+    game_dir: &PathBuf,
+) -> Result<Vec<String>, Box<dyn Error + Send + Sync>> {
+    let versions_dir = game_dir.join("versions");
+    let mut installed = Vec::new();
+
+    if !versions_dir.exists() {
+        return Ok(installed);
+    }
+
+    let mut entries = tokio::fs::read_dir(&versions_dir).await?;
+    while let Some(entry) = entries.next_entry().await? {
+        let name = entry.file_name().to_string_lossy().to_string();
+        if name.starts_with("fabric-loader-") {
+            // Verify the JSON file exists
+            let json_path = entry.path().join(format!("{}.json", name));
+            if json_path.exists() {
+                installed.push(name);
+            }
+        }
+    }
+
+    Ok(installed)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_generate_version_id() {
+        assert_eq!(
+            generate_version_id("1.20.4", "0.15.6"),
+            "fabric-loader-0.15.6-1.20.4"
+        );
+    }
+}