Added settings window.

src/PathManager.swift

@@ -0,0 +1,85 @@
+import AppKit
+import OSLog
+
+final class PathManager {
+    fileprivate static let logger = Logger(
+        subsystem: Bundle.main.bundleIdentifier!,
+        category: String(describing: PathManager.self)
+    )
+
+    static let shared = PathManager()
+
+    // TODO: Filesystem events to watch changes on these directories and
+    //       rebuild index when needed.
+    // NOTE: These are default paths where MacOS's default programs are
+    //       stored. This list should be updated if something changes in
+    //       newer MacOS version.
+    static let defaultPaths = ["/Applications", "/System/Applications",
+        "/System/Applications/Utilities", "/System/Library/CoreServices",
+        "/Applications/Xcode.app/Contents/Applications",
+        "/System/Library/CoreServices/Applications"]
+    var userPaths: [String] = []
+    private(set) var programs: [Program] = []
+
+    private let fileManager = FileManager.default
+
+    private init() {
+        if let paths =
+            UserDefaults.standard.stringArray(forKey: "programPaths")
+        {
+            for path in paths {
+                addPath(path)
+            }
+        } else {
+            userPaths += Self.defaultPaths
+        }
+    }
+
+    deinit {}
+
+    public func addPath(_ path: String) {
+        if !userPaths.contains(path) {
+            userPaths.append(path)
+        }
+    }
+
+    public func removePath(_ path: String) {
+        userPaths.removeAll { $0 == path }
+    }
+
+    public func removeEmpty() {
+        userPaths.removeAll { $0.isEmpty }
+    }
+
+    public func savePaths() {
+        UserDefaults.standard.set(userPaths, forKey: "programPaths")
+    }
+
+    public func reset() {
+        userPaths = []
+        userPaths += Self.defaultPaths
+        savePaths()
+    }
+
+    public func rebuildIndex() {
+        programs.removeAll(keepingCapacity: true)
+        for path in userPaths {
+            do {
+                let items = try fileManager.contentsOfDirectory(
+                    atPath: path)
+                for item in items {
+                    let name = String(item.dropLast(4))
+                    if item.hasSuffix(".app") {
+                        if !programs.contains(where: { name == $0.name }) {
+                            programs.append(
+                                Program(
+                                    path: path, name: name, ext: ".app"))
+                        }
+                    }
+                }
+            } catch {
+                Self.logger.error("Error reading directory: \(error.localizedDescription, privacy: .public)")
+            }
+        }
+    }
+}