LibDSP: Introduce the Keyboard

This is a class for handling user MIDI input, which is combined by the
Track with roll note data if applicable.

Userland/Libraries/LibDSP/Keyboard.h

@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2021-2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <AK/RefCounted.h>
+#include <LibDSP/Music.h>
+#include <LibDSP/Transport.h>
+
+namespace LibDSP {
+
+class Keyboard : public RefCounted<Keyboard> {
+
+public:
+    enum class Direction : bool {
+        Down,
+        Up,
+    };
+    enum class Switch : bool {
+        Off,
+        On,
+    };
+
+    Keyboard(NonnullRefPtr<Transport> transport)
+        : m_transport(move(transport))
+    {
+    }
+
+    u8 virtual_keyboard_octave() const { return m_virtual_keyboard_octave; }
+    u8 virtual_keyboard_octave_base() const { return (m_virtual_keyboard_octave - octave_min) * 12; }
+    // Automatically clips the octave between the minimum and maximum.
+    void change_virtual_keyboard_octave(Direction);
+    // Errors out if the set octave is out of range.
+    ErrorOr<void> set_virtual_keyboard_octave(u8 octave);
+
+    void set_keyboard_note(u8 pitch, Switch note_switch);
+    void set_keyboard_note_in_active_octave(i8 octave_offset, Switch note_switch);
+
+    RollNotes const& notes() const { return m_pressed_notes; }
+    Optional<RollNote> note_at(u8 pitch) const { return m_pressed_notes.get(pitch); }
+    bool is_pressed(u8 pitch) const;
+    bool is_pressed_in_active_octave(i8 octave_offset) const;
+
+private:
+    u8 m_virtual_keyboard_octave { 4 };
+    RollNotes m_pressed_notes;
+
+    NonnullRefPtr<Transport> m_transport;
+
+    static constexpr int const octave_min = 1;
+    static constexpr int const octave_max = 7;
+};
+
+}