Added barebones OSInterface with hotkey registration.

src/model/OSInterface.java

+package model;
+
+import com.sun.jna.platform.win32.User32;
+import com.sun.jna.platform.win32.WinDef;
+
+import java.util.HashMap;
+
+/** Singleton class which interfaces with windows. */
+public class OSInterface implements HotkeyDetector, HotkeyRegistration, InputEmulator, OSSettingsWriter {
+    private static OSInterface instance = null;
+
+    private User32 user32 = User32.INSTANCE;
+    private WinDef.HWND hwnd;
+    private HashMap<Integer, Hotkey> registeredKeys;
+
+    private OSInterface() {
+        registeredKeys = new HashMap<>();
+    }
+
+    /**
+     * Gets the OSInterface instance.
+     */
+    public static OSInterface getInstance() {
+        if (instance == null)
+            instance = new OSInterface();
+
+        return instance;
+    }
+
+    /**
+     * Sets the HWND to use for interfacing with the OS.
+     * @param hwnd The HWND of a window.
+     */
+    public void setHWND(WinDef.HWND hwnd) {
+        this.hwnd = hwnd;
+    }
+
+    @Override
+    public boolean registerHotkey(Hotkey hotkey) {
+        if (registeredKeys.containsKey(hotkey.getID()))
+            return false;
+
+        boolean success = user32.RegisterHotKey(hwnd, hotkey.getID(), hotkey.getModifier(), hotkey.getKeyCode());
+        if (success)
+            registeredKeys.put(hotkey.getID(), hotkey);
+
+        return success;
+    }
+
+    @Override
+    public boolean unregisterHotkey(int id) {
+        if (!registeredKeys.containsKey(id))
+            return true;
+
+        boolean success = user32.UnregisterHotKey(hwnd.getPointer(), id);
+        if (success)
+            registeredKeys.remove(id);
+
+        return success;
+    }
+
+    @Override
+    public boolean setMouseSpeed(int speed) {
+        return false;
+    }
+
+    @Override
+    public boolean wasPressed(int id) {
+        return false;
+    }
+
+    @Override
+    public void sendKey(int keyCode, boolean release) {
+
+    }
+}
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