SoundPlayer: Implement playlist shuffle mode

The shuffling algorithm uses a naïve bloom filter to provide random
uniformity, avoiding items that were recently played.  With 32 bits,
double hashing, and an error rate of ~10%, this bloom filter should
be able to hold around ~16 keys, which should be sufficient to give the
illusion of fairness to the shuffling algorithm.

This avoids having to shuffle the playlist itself (user might have
spent quite a bit of time to sort them, so it's not a good idea to mess
with it), or having to create a proxy model that shuffles (that could
potentially use quite a bit of memory).

Userland/Applications/SoundPlayer/Player.cpp

@@ -92,6 +92,15 @@ void Player::set_volume(double volume)
     volume_changed(m_volume);
 }
 
+void Player::set_shuffle_mode(ShuffleMode mode)
+{
+    if (m_shuffle_mode != mode) {
+        m_shuffle_mode = mode;
+        m_playlist.set_shuffling(mode == ShuffleMode::Shuffling);
+        shuffle_mode_changed(mode);
+    }
+}
+
 void Player::play()
 {
     m_playback_manager.play();

Userland/Applications/SoundPlayer/Player.h

@@ -24,6 +24,10 @@ public:
         File,
         Playlist,
     };
+    enum class ShuffleMode {
+        None,
+        Shuffling,
+    };
 
     explicit Player(Audio::ClientConnection& audio_client_connection);
     virtual ~Player() { }
@@ -34,10 +38,13 @@ public:
     StringView loaded_filename() const { return m_loaded_filename; }
 
     PlayState play_state() const { return m_play_state; }
-    void set_play_state(PlayState state);
+    void set_play_state(PlayState);
 
     LoopMode loop_mode() const { return m_loop_mode; }
-    void set_loop_mode(LoopMode mode);
+    void set_loop_mode(LoopMode);
+
+    ShuffleMode shuffle_mode() const { return m_shuffle_mode; }
+    void set_shuffle_mode(ShuffleMode);
 
     double volume() const { return m_volume; }
     void set_volume(double value);
@@ -52,11 +59,12 @@ public:
     virtual void loop_mode_changed(LoopMode) = 0;
     virtual void time_elapsed(int) = 0;
     virtual void file_name_changed(StringView) = 0;
-    virtual void playlist_loaded(StringView, bool) { }
+    virtual void playlist_loaded(StringView, bool) = 0;
-    virtual void audio_load_error(StringView, StringView) { }
+    virtual void audio_load_error(StringView, StringView) = 0;
-    virtual void volume_changed(double) { }
+    virtual void shuffle_mode_changed(ShuffleMode) = 0;
-    virtual void total_samples_changed(int) { }
+    virtual void volume_changed(double) = 0;
-    virtual void sound_buffer_played(RefPtr<Audio::Buffer>, [[maybe_unused]] int sample_rate, [[maybe_unused]] int samples_played) { }
+    virtual void total_samples_changed(int) = 0;
+    virtual void sound_buffer_played(RefPtr<Audio::Buffer>, [[maybe_unused]] int sample_rate, [[maybe_unused]] int samples_played) = 0;
 
 protected:
     void done_initializing()
@@ -71,6 +79,7 @@ private:
     Playlist m_playlist;
     PlayState m_play_state;
     LoopMode m_loop_mode;
+    ShuffleMode m_shuffle_mode;
 
     Audio::ClientConnection& m_audio_client_connection;
     PlaybackManager m_playback_manager;

Userland/Applications/SoundPlayer/Playlist.cpp

@@ -8,6 +8,7 @@
 #include "Playlist.h"
 
 #include <AK/LexicalPath.h>
+#include <AK/Random.h>
 #include <LibAudio/Loader.h>
 #include <LibGUI/MessageBox.h>
 
@@ -33,7 +34,7 @@ void Playlist::try_fill_missing_info(Vector<M3UEntry>& entries, StringView path)
     Vector<M3UEntry*> to_delete;
 
     for (auto& entry : entries) {
-        if (!LexicalPath(entry.path).is_absolute())
+        if (!LexicalPath { entry.path }.is_absolute())
             entry.path = String::formatted("{}/{}", playlist_path.dirname(), entry.path);
 
         if (!entry.extended_info->file_size_in_bytes.has_value()) {
@@ -69,11 +70,35 @@ StringView Playlist::next()
             return {};
         m_next_index_to_play = 0;
     }
+
     auto next = m_model->items().at(m_next_index_to_play).path;
+    if (!shuffling()) {
         m_next_index_to_play++;
         return next;
     }
 
+    // Try a few times getting an item to play that has not been
+    // recently played.  But do not try too hard, as we don't want
+    // to wait forever.
+    int shuffle_try;
+    int const max_times_to_try = min(4, size());
+    for (shuffle_try = 0; shuffle_try < max_times_to_try; shuffle_try++) {
+        if (!m_previously_played_paths.maybe_contains(next))
+            break;
+
+        m_next_index_to_play = get_random_uniform(size());
+        next = m_model->items().at(m_next_index_to_play).path;
+    }
+    if (shuffle_try == max_times_to_try) {
+        // If we tried too much, maybe it's time to try resetting
+        // the bloom filter and start over.
+        m_previously_played_paths.reset();
+    }
+
+    m_previously_played_paths.add(next);
+    return next;
+}
+
 StringView Playlist::previous()
 {
     m_next_index_to_play--;

Userland/Applications/SoundPlayer/Playlist.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, the SerenityOS developers.
+ * Copyright (c) 2021, Leandro A. F. Pereira <leandro@tia.mat.br>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -8,6 +9,7 @@
 
 #include "M3UParser.h"
 #include "PlaylistWidget.h"
+#include <AK/StringHash.h>
 #include <AK/StringView.h>
 #include <AK/Vector.h>
 
@@ -29,11 +31,40 @@ public:
     void set_looping(bool looping) { m_looping = looping; }
     bool looping() const { return m_looping; }
 
+    void set_shuffling(bool shuffling) { m_shuffling = shuffling; }
+    bool shuffling() const { return m_shuffling; }
+
 private:
+    // This naïve bloom filter is used in the shuffling algorithm to
+    // provide random uniformity, avoiding playing items that were recently
+    // played.
+    class BloomFilter {
+    public:
+        void reset() { m_bitmap = 0; }
+        void add(const StringView key) { m_bitmap |= mask_for_key(key); }
+        bool maybe_contains(const StringView key) const
+        {
+            auto mask = mask_for_key(key);
+            return (m_bitmap & mask) == mask;
+        }
+
+    private:
+        u64 mask_for_key(StringView key) const
+        {
+            auto key_chars = key.characters_without_null_termination();
+            auto hash1 = string_hash(key_chars, key.length(), 0xdeadbeef);
+            auto hash2 = string_hash(key_chars, key.length(), 0xbebacafe);
+            return 1ULL << (hash1 & 63) | 1ULL << (hash2 & 63);
+        }
+        u64 m_bitmap { 0 };
+    };
+
     void try_fill_missing_info(Vector<M3UEntry>&, StringView);
 
     RefPtr<PlaylistModel> m_model;
     bool m_looping { false };
+    bool m_shuffling { false };
 
+    BloomFilter m_previously_played_paths;
     int m_next_index_to_play { 0 };
 };

Userland/Applications/SoundPlayer/SoundPlayerWidgetAdvancedView.cpp

@@ -157,8 +157,7 @@ void SoundPlayerWidgetAdvancedView::set_playlist_visible(bool visible)
 
 void SoundPlayerWidgetAdvancedView::play_state_changed(Player::PlayState state)
 {
-    m_back_button->set_enabled(playlist().size() > 1);
+    sync_previous_next_buttons();
-    m_next_button->set_enabled(playlist().size() > 1);
 
     m_play_button->set_enabled(state != PlayState::NoFileLoaded);
     m_play_button->set_icon(state == PlayState::Playing ? *m_pause_icon : *m_play_icon);
@@ -172,6 +171,17 @@ void SoundPlayerWidgetAdvancedView::loop_mode_changed(Player::LoopMode)
 {
 }
 
+void SoundPlayerWidgetAdvancedView::sync_previous_next_buttons()
+{
+    m_back_button->set_enabled(playlist().size() > 1 && !playlist().shuffling());
+    m_next_button->set_enabled(playlist().size() > 1);
+}
+
+void SoundPlayerWidgetAdvancedView::shuffle_mode_changed(Player::ShuffleMode)
+{
+    sync_previous_next_buttons();
+}
+
 void SoundPlayerWidgetAdvancedView::time_elapsed(int seconds)
 {
     m_timestamp_label->set_text(String::formatted("Elapsed: {:02}:{:02}:{:02}", seconds / 3600, seconds / 60, seconds % 60));

Userland/Applications/SoundPlayer/SoundPlayerWidgetAdvancedView.h

@@ -38,6 +38,7 @@ public:
 
     virtual void play_state_changed(PlayState) override;
     virtual void loop_mode_changed(LoopMode) override;
+    virtual void shuffle_mode_changed(ShuffleMode) override;
     virtual void time_elapsed(int) override;
     virtual void file_name_changed(StringView) override;
     virtual void playlist_loaded(StringView, bool) override;
@@ -50,6 +51,8 @@ protected:
     void keydown_event(GUI::KeyEvent&) override;
 
 private:
+    void sync_previous_next_buttons();
+
     void drop_event(GUI::DropEvent& event) override;
     GUI::Window& m_window;
 

Userland/Applications/SoundPlayer/main.cpp

@@ -98,6 +98,14 @@ int main(int argc, char** argv)
         playlist_toggle->set_checked(true);
     playback_menu.add_action(playlist_toggle);
 
+    auto shuffle_mode = GUI::Action::create_checkable("S&huffle Playlist", [&](auto& action) {
+        if (action.is_checked())
+            player->set_shuffle_mode(Player::ShuffleMode::Shuffling);
+        else
+            player->set_shuffle_mode(Player::ShuffleMode::None);
+    });
+    playback_menu.add_action(shuffle_mode);
+
     auto& visualization_menu = window->add_menu("&Visualization");
     GUI::ActionGroup visualization_actions;
     visualization_actions.set_exclusive(true);