Add FUSE external mapping support, BG3/Oblivion Remastered fixes, fomod-plus and NaK integration

FUSE VFS now deploys non-data-dir mod mappings (Paks, OBSE, UE4SS, etc.)
via real symlinks and injects file-level data-dir mappings (plugins.txt,
loadorder.txt) into the VFS tree. Fixes game launches for Oblivion
Remastered (Root Builder path resolution, script extender support) and
BG3 (Wine prefix documents directory, file mapper symlinks on Linux).

Vendors mo2-fomod-plus plugin and NaK crate for FOMOD installer and
game finder/runtime support.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 359 insertions, 0 deletions

diff --git a/libs/nak/src/installers/symlinks.rs b/libs/nak/src/installers/symlinks.rs
new file mode 100644
index 0000000..ef8cbb4
--- /dev/null
+++ b/libs/nak/src/installers/symlinks.rs
@@ -0,0 +1,359 @@
+//! Symlink management for NaK prefixes
+//!
+//! Creates symlinks FROM NaK prefix TO game prefixes.
+//! Data stays in the game prefix, NaK just has links pointing to it.
+//!
+//! This inverted approach means:
+//! - Game saves remain in their original location (Steam cloud sync works)
+//! - NaK prefix provides unified access to all game data
+//! - No data duplication or sync issues
+//!
+//! NaK Tools folder contains convenience symlinks pointing INTO the prefix
+//! for easy access to Documents, AppData, etc.
+
+// Allow unused items - some functions are public API for future use
+#![allow(dead_code)]
+
+use std::fs;
+use std::path::Path;
+
+use crate::game_finder::{detect_all_games, Game, GameScanResult};
+use crate::logging::{log_info, log_warning};
+
+// ============================================================================
+// Public API
+// ============================================================================
+
+/// Create symlinks from NaK prefix to game prefixes for all detected games
+///
+/// This creates symlinks in the NaK prefix pointing to the actual save/config
+/// folders in each game's own prefix. The symlink direction is:
+///
+/// NaK/Documents/My Games/Skyrim -> game_prefix/Documents/My Games/Skyrim
+/// NaK/AppData/Local/Skyrim -> game_prefix/AppData/Local/Skyrim
+///
+/// Data stays in the game prefix (preserving Steam Cloud sync), while NaK
+/// provides unified access through symlinks.
+pub fn create_game_symlinks(nak_prefix: &Path, games: &[Game]) {
+    let users_dir = nak_prefix.join("drive_c/users");
+    let username = find_prefix_username(&users_dir);
+    let user_dir = users_dir.join(&username);
+
+    let documents = user_dir.join("Documents");
+    let my_games = documents.join("My Games");
+    let appdata_local = user_dir.join("AppData/Local");
+    let appdata_roaming = user_dir.join("AppData/Roaming");
+
+    // Ensure base directories exist (real folders in NaK prefix)
+    let _ = fs::create_dir_all(&my_games);
+    let _ = fs::create_dir_all(&appdata_local);
+    let _ = fs::create_dir_all(&appdata_roaming);
+
+    let mut linked_count = 0;
+
+    for game in games {
+        // Skip games without prefixes
+        let Some(game_prefix) = &game.prefix_path else {
+            continue;
+        };
+
+        // Discover the game prefix's user directory
+        let game_users_dir = game_prefix.join("drive_c/users");
+        let game_username = find_prefix_username(&game_users_dir);
+        let game_user_dir = game_users_dir.join(&game_username);
+
+        // Scan and symlink ALL folders in the game prefix's Documents/My Games/
+        linked_count += scan_and_link_all(
+            &my_games,
+            &game_user_dir.join("Documents/My Games"),
+            "Documents/My Games",
+            &game.name,
+            game_prefix,
+        );
+
+        // Also link the Documents folder itself for non-My Games entries
+        // (some games put saves directly in Documents/<GameName>)
+        linked_count += scan_and_link_all(
+            &documents,
+            &game_user_dir.join("Documents"),
+            "Documents",
+            &game.name,
+            game_prefix,
+        );
+
+        // Scan and symlink ALL folders in AppData/Local/
+        linked_count += scan_and_link_all(
+            &appdata_local,
+            &game_user_dir.join("AppData/Local"),
+            "AppData/Local",
+            &game.name,
+            game_prefix,
+        );
+
+        // Scan and symlink ALL folders in AppData/Roaming/
+        linked_count += scan_and_link_all(
+            &appdata_roaming,
+            &game_user_dir.join("AppData/Roaming"),
+            "AppData/Roaming",
+            &game.name,
+            game_prefix,
+        );
+    }
+
+    if linked_count > 0 {
+        log_info(&format!(
+            "Created {} symlinks to game prefixes",
+            linked_count
+        ));
+    }
+
+    // Create "My Documents" symlink for compatibility
+    let my_documents = user_dir.join("My Documents");
+    if !my_documents.exists() && fs::symlink_metadata(&my_documents).is_err() {
+        if let Err(e) = std::os::unix::fs::symlink("Documents", &my_documents) {
+            log_warning(&format!("Failed to create My Documents symlink: {}", e));
+        }
+    }
+}
+
+/// Create NaK Tools convenience symlinks pointing INTO the prefix
+///
+/// Creates symlinks in NaK Tools folder for easy access:
+/// - NaK Tools/Prefix Documents -> prefix/drive_c/users/<user>/Documents
+/// - NaK Tools/Prefix AppData Local -> prefix/drive_c/users/<user>/AppData/Local
+/// - NaK Tools/Prefix AppData Roaming -> prefix/drive_c/users/<user>/AppData/Roaming
+pub fn create_nak_tools_symlinks(tools_dir: &Path, prefix_path: &Path) {
+    let users_dir = prefix_path.join("drive_c/users");
+    let username = find_prefix_username(&users_dir);
+    let user_dir = users_dir.join(&username);
+
+    // Symlink: NaK Tools/Prefix Documents -> prefix Documents
+    let documents_link = tools_dir.join("Prefix Documents");
+    let documents_target = user_dir.join("Documents");
+    create_or_update_symlink(&documents_link, &documents_target, "Prefix Documents");
+
+    // Symlink: NaK Tools/Prefix AppData Local -> prefix AppData/Local
+    let appdata_local_link = tools_dir.join("Prefix AppData Local");
+    let appdata_local_target = user_dir.join("AppData/Local");
+    create_or_update_symlink(&appdata_local_link, &appdata_local_target, "Prefix AppData Local");
+
+    // Symlink: NaK Tools/Prefix AppData Roaming -> prefix AppData/Roaming
+    let appdata_roaming_link = tools_dir.join("Prefix AppData Roaming");
+    let appdata_roaming_target = user_dir.join("AppData/Roaming");
+    create_or_update_symlink(&appdata_roaming_link, &appdata_roaming_target, "Prefix AppData Roaming");
+
+    log_info("Created NaK Tools convenience symlinks to prefix folders");
+}
+
+/// Create or update a symlink
+fn create_or_update_symlink(link_path: &Path, target: &Path, name: &str) {
+    // Remove existing symlink or file
+    if link_path.exists() || fs::symlink_metadata(link_path).is_ok() {
+        let _ = fs::remove_file(link_path);
+        let _ = fs::remove_dir_all(link_path);
+    }
+
+    // Create symlink
+    if let Err(e) = std::os::unix::fs::symlink(target, link_path) {
+        log_warning(&format!("Failed to create {} symlink: {}", name, e));
+    }
+}
+
+/// Create symlinks for all detected games
+///
+/// Convenience function that detects games and creates symlinks in one call.
+pub fn create_game_symlinks_auto(nak_prefix: &Path) -> GameScanResult {
+    let result = detect_all_games();
+    create_game_symlinks(nak_prefix, &result.games);
+    result
+}
+
+/// Ensure only the Temp directory exists in AppData/Local
+///
+/// MO2 and other tools require AppData/Local/Temp to exist.
+/// We create only this essential directory, leaving other game-specific
+/// folders to be symlinked from game prefixes.
+pub fn ensure_temp_directory(prefix_path: &Path) {
+    let users_dir = prefix_path.join("drive_c/users");
+    let username = find_prefix_username(&users_dir);
+    let user_dir = users_dir.join(&username);
+
+    let temp_dir = user_dir.join("AppData/Local/Temp");
+    if let Err(e) = fs::create_dir_all(&temp_dir) {
+        log_warning(&format!("Failed to create Temp directory: {}", e));
+    } else {
+        log_info("Ensured AppData/Local/Temp directory exists");
+    }
+}
+
+// ============================================================================
+// Internal Functions
+// ============================================================================
+
+/// Directories to skip when scanning prefix folders for symlinking.
+/// These are Wine/Proton internal or system dirs, not game data.
+const SKIP_DIRS: &[&str] = &[
+    "Temp", "Microsoft", "wine", "Public", "root",
+    "Application Data", "Cookies", "Local Settings",
+    "NetHood", "PrintHood", "Recent", "SendTo",
+    "Start Menu", "Templates", "My Documents", "My Music",
+    "My Pictures", "My Videos", "Desktop", "Downloads",
+    "Favorites", "Links", "Saved Games", "Searches",
+    "Contacts", "3D Objects",
+];
+
+/// Scan all subdirectories in a game prefix folder and create symlinks
+/// for each one in the corresponding NaK prefix folder.
+///
+/// Returns the number of symlinks created.
+fn scan_and_link_all(
+    nak_base: &Path,
+    game_base: &Path,
+    label: &str,
+    game_name: &str,
+    _game_prefix: &Path,
+) -> usize {
+    if !game_base.is_dir() {
+        return 0;
+    }
+
+    let Ok(entries) = fs::read_dir(game_base) else {
+        return 0;
+    };
+
+    let mut count = 0;
+    for entry in entries.flatten() {
+        // Only symlink directories (game folders), not loose files
+        if !entry.path().is_dir() {
+            continue;
+        }
+
+        let folder_name = entry.file_name().to_string_lossy().to_string();
+
+        // Skip Wine/system internal directories
+        if SKIP_DIRS.iter().any(|&s| s.eq_ignore_ascii_case(&folder_name)) {
+            continue;
+        }
+
+        // Skip if it's "My Games" and we're scanning Documents (handled separately)
+        if label == "Documents" && folder_name == "My Games" {
+            continue;
+        }
+
+        let nak_path = nak_base.join(&folder_name);
+        let source_path = entry.path();
+
+        if create_symlink_if_needed(&nak_path, &source_path, game_name, label, &folder_name) {
+            count += 1;
+        }
+    }
+
+    count
+}
+
+/// Create a symlink if the target doesn't already exist or is already correct.
+///
+/// Returns true if a symlink was created (or already existed correctly).
+fn create_symlink_if_needed(
+    nak_path: &Path,
+    source_path: &Path,
+    game_name: &str,
+    label: &str,
+    folder_name: &str,
+) -> bool {
+    // Check if target already exists
+    if nak_path.exists() || fs::symlink_metadata(nak_path).is_ok() {
+        // Check if it's already a symlink to the correct location
+        if let Ok(target) = fs::read_link(nak_path) {
+            if target == source_path {
+                return true; // Already correctly linked
+            }
+        }
+        // Something else exists here, don't overwrite
+        return false;
+    }
+
+    // Ensure parent directory exists
+    if let Some(parent) = nak_path.parent() {
+        let _ = fs::create_dir_all(parent);
+    }
+
+    // Create the symlink
+    match std::os::unix::fs::symlink(source_path, nak_path) {
+        Ok(()) => {
+            log_info(&format!(
+                "Linked {}/{} -> {} ({})",
+                label,
+                folder_name,
+                source_path.display(),
+                game_name,
+            ));
+            true
+        }
+        Err(e) => {
+            log_warning(&format!(
+                "Failed to create symlink for {} ({}/{}): {}",
+                game_name, label, folder_name, e
+            ));
+            false
+        }
+    }
+}
+
+/// Find the username from a Wine prefix users directory
+fn find_prefix_username(users_dir: &Path) -> String {
+    if let Ok(entries) = fs::read_dir(users_dir) {
+        for entry in entries.flatten() {
+            let name = entry.file_name().to_string_lossy().to_string();
+            if name != "Public" && name != "root" {
+                return name;
+            }
+        }
+    }
+    "steamuser".to_string()
+}
+
+// ============================================================================
+// Oblivion Lowercase INI Symlinks
+// ============================================================================
+
+/// Create lowercase INI symlinks for Oblivion (some tools expect lowercase)
+pub fn create_oblivion_ini_symlinks(prefix_path: &Path) {
+    let users_dir = prefix_path.join("drive_c/users");
+    let username = find_prefix_username(&users_dir);
+    let oblivion_dir = users_dir
+        .join(&username)
+        .join("Documents/My Games/Oblivion");
+
+    if !oblivion_dir.exists() {
+        return;
+    }
+
+    create_lowercase_ini_symlink(&oblivion_dir, "Oblivion.ini", "oblivion.ini");
+    create_lowercase_ini_symlink(&oblivion_dir, "OblivionPrefs.ini", "oblivionprefs.ini");
+}
+
+/// Create a lowercase symlink for an INI file
+fn create_lowercase_ini_symlink(dir: &Path, original: &str, lowercase: &str) {
+    let original_path = dir.join(original);
+    let lowercase_path = dir.join(lowercase);
+
+    // Only create if original exists and lowercase doesn't
+    if original_path.exists()
+        && !lowercase_path.exists()
+        && fs::symlink_metadata(&lowercase_path).is_err()
+    {
+        // Create relative symlink (just the filename)
+        if let Err(e) = std::os::unix::fs::symlink(original, &lowercase_path) {
+            log_warning(&format!(
+                "Failed to create lowercase symlink {} -> {}: {}",
+                lowercase, original, e
+            ));
+        } else {
+            log_info(&format!(
+                "Created lowercase INI symlink: {} -> {}",
+                lowercase, original
+            ));
+        }
+    }
+}