HackStudio: Rethink the "project" concept to be about a directory

Instead of having .hsp files that determine which files are members
of a project, a project is now an entire directory tree instead.

This feels a lot less cumbersome to work with, and removes a fair
amount of busywork that would otherwise be expected from the user.

This patch refactors large parts of HackStudio to implement the new
way of thinking. I've probably missed some details here and there,
but generally I think it's pretty OK.

6 files changed, 83 insertions, 465 deletions

diff --git a/DevTools/HackStudio/Editor.cpp b/DevTools/HackStudio/Editor.cpp
index 7a6972fb08..660ff1c5a2 100644
--- a/DevTools/HackStudio/Editor.cpp
+++ b/DevTools/HackStudio/Editor.cpp
@@ -465,7 +465,7 @@ void Editor::set_document(GUI::TextDocument& doc)
     switch (code_document.language()) {
     case Language::Cpp:
         set_syntax_highlighter(make<GUI::CppSyntaxHighlighter>());
-        m_language_client = get_language_client<LanguageClients::Cpp::ServerConnection>(project().root_directory());
+        m_language_client = get_language_client<LanguageClients::Cpp::ServerConnection>(project().root_path());
         break;
     case Language::JavaScript:
         set_syntax_highlighter(make<GUI::JSSyntaxHighlighter>());
@@ -475,16 +475,15 @@ void Editor::set_document(GUI::TextDocument& doc)
         break;
     case Language::Shell:
         set_syntax_highlighter(make<GUI::ShellSyntaxHighlighter>());
-        m_language_client = get_language_client<LanguageClients::Shell::ServerConnection>(project().root_directory());
+        m_language_client = get_language_client<LanguageClients::Shell::ServerConnection>(project().root_path());
         break;
     default:
         set_syntax_highlighter(nullptr);
     }
 
     if (m_language_client) {
-        auto full_file_path = String::formatted("{}/{}", project().root_directory(), code_document.file_path());
-        dbg() << "Opening " << full_file_path;
-        int fd = open(full_file_path.characters(), O_RDONLY | O_NOCTTY);
+        dbgln("Opening {}", code_document.file_path());
+        int fd = open(code_document.file_path().string().characters(), O_RDONLY | O_NOCTTY);
         if (fd < 0) {
             perror("open");
             return;
diff --git a/DevTools/HackStudio/HackStudioWidget.cpp b/DevTools/HackStudio/HackStudioWidget.cpp
index 2ecf6f808e..e373664110 100644
--- a/DevTools/HackStudio/HackStudioWidget.cpp
+++ b/DevTools/HackStudio/HackStudioWidget.cpp
@@ -109,6 +109,10 @@ HackStudioWidget::HackStudioWidget(const String& path_to_project)
 
     m_right_hand_splitter = outer_splitter.add<GUI::VerticalSplitter>();
     m_right_hand_stack = m_right_hand_splitter->add<GUI::StackWidget>();
+
+    // Put a placeholder widget front & center since we don't have a file open yet.
+    m_right_hand_stack->add<GUI::Widget>();
+
     create_form_editor(*m_right_hand_stack);
 
     m_diff_viewer = m_right_hand_stack->add<DiffViewer>();
@@ -174,14 +178,13 @@ void HackStudioWidget::on_action_tab_change()
     reinterpret_cast<GitWidget*>(git_widget)->refresh();
 }
 
-void HackStudioWidget::open_project(String filename)
+void HackStudioWidget::open_project(const String& root_path)
 {
-    LexicalPath lexical_path(filename);
-    if (chdir(lexical_path.dirname().characters()) < 0) {
+    if (chdir(root_path.characters()) < 0) {
         perror("chdir");
         exit(1);
     }
-    m_project = Project::load_from_file(filename);
+    m_project = Project::open_with_root_path(root_path);
     ASSERT(m_project);
     if (m_project_tree_view) {
         m_project_tree_view->set_model(m_project->model());
@@ -240,7 +243,12 @@ void HackStudioWidget::open_file(const String& filename)
     }
 
     m_currently_open_file = filename;
-    window()->set_title(String::formatted("{} - HackStudio", m_currently_open_file));
+
+    String relative_file_path = m_currently_open_file;
+    if (m_currently_open_file.starts_with(m_project->root_path()))
+        relative_file_path = m_currently_open_file.substring(m_project->root_path().length() + 1);
+
+    window()->set_title(String::formatted("{} - {} - HackStudio", relative_file_path, m_project->name()));
     m_project_tree_view->update();
 
     current_editor_wrapper().filename_label().set_text(filename);
@@ -277,14 +285,12 @@ NonnullRefPtr<GUI::Menu> HackStudioWidget::create_project_tree_view_context_menu
 {
     m_open_selected_action = create_open_selected_action();
     m_new_action = create_new_action();
-    m_add_existing_file_action = create_add_existing_file_action();
     m_delete_action = create_delete_action();
     auto project_tree_view_context_menu = GUI::Menu::construct("Project Files");
     project_tree_view_context_menu->add_action(*m_open_selected_action);
     // TODO: Rename, cut, copy, duplicate with new name, show containing folder ...
     project_tree_view_context_menu->add_separator();
     project_tree_view_context_menu->add_action(*m_new_action);
-    project_tree_view_context_menu->add_action(*m_add_existing_file_action);
     project_tree_view_context_menu->add_action(*m_delete_action);
     return project_tree_view_context_menu;
 }
@@ -300,11 +306,6 @@ NonnullRefPtr<GUI::Action> HackStudioWidget::create_new_action()
             GUI::MessageBox::show(window(), String::formatted("Failed to create '{}'", filename), "Error", GUI::MessageBox::Type::Error);
             return;
         }
-        if (!m_project->add_file(filename)) {
-            GUI::MessageBox::show(window(), String::formatted("Failed to add '{}' to project", filename), "Error", GUI::MessageBox::Type::Error);
-            // FIXME: Should we unlink the file here maybe?
-            return;
-        }
         m_project_tree_view->toggle_index(m_project_tree_view->model()->index(0, 0));
         open_file(filename);
     });
@@ -322,25 +323,8 @@ NonnullRefPtr<GUI::Action> HackStudioWidget::create_open_selected_action()
     return open_selected_action;
 }
 
-NonnullRefPtr<GUI::Action> HackStudioWidget::create_add_existing_file_action()
-{
-    return GUI::Action::create("Add existing file to project...", Gfx::Bitmap::load_from_file("/res/icons/16x16/open.png"), [this](auto&) {
-        auto result = GUI::FilePicker::get_open_filepath(window(), "Add existing file to project");
-        if (!result.has_value())
-            return;
-        auto& filename = result.value();
-        if (!m_project->add_file(filename)) {
-            GUI::MessageBox::show(window(), String::formatted("Failed to add '{}' to project", filename), "Error", GUI::MessageBox::Type::Error);
-            return;
-        }
-        m_project_tree_view->toggle_index(m_project_tree_view->model()->index(0, 0));
-        open_file(filename);
-    });
-}
-
 NonnullRefPtr<GUI::Action> HackStudioWidget::create_delete_action()
 {
-
     auto delete_action = GUI::CommonActions::make_delete_action([this](const GUI::Action&) {
         auto files = selected_file_names();
         if (files.is_empty())
@@ -348,9 +332,9 @@ NonnullRefPtr<GUI::Action> HackStudioWidget::create_delete_action()
 
         String message;
         if (files.size() == 1) {
-            message = String::formatted("Really remove {} from the project?", LexicalPath(files[0]).basename());
+            message = String::formatted("Really remove {} from disk?", LexicalPath(files[0]).basename());
         } else {
-            message = String::formatted("Really remove {} files from the project?", files.size());
+            message = String::formatted("Really remove {} files from disk?", files.size());
         }
 
         auto result = GUI::MessageBox::show(window(),
@@ -362,11 +346,8 @@ NonnullRefPtr<GUI::Action> HackStudioWidget::create_delete_action()
             return;
 
         for (auto& file : files) {
-            if (m_project->remove_file(file)) {
-                m_open_files_vector.remove_first_matching([&](auto& filename) {
-                    return filename == file;
-                });
-                m_open_files_view->model()->update();
+            if (1) {
+                // FIXME: Remove `file` from disk
             } else {
                 GUI::MessageBox::show(window(),
                     String::formatted("Removing file {} from the project failed.", file),
@@ -455,7 +436,6 @@ NonnullRefPtr<GUI::Action> HackStudioWidget::create_open_action()
         if (!open_path.has_value())
             return;
         open_project(open_path.value());
-        open_file(m_project->default_file());
         update_actions();
     });
 }
@@ -522,10 +502,6 @@ void HackStudioWidget::reveal_action_tab(GUI::Widget& widget)
 NonnullRefPtr<GUI::Action> HackStudioWidget::create_debug_action()
 {
     return GUI::Action::create("Debug", Gfx::Bitmap::load_from_file("/res/icons/16x16/debug-run.png"), [this](auto&) {
-        if (m_project->type() != ProjectType::Cpp) {
-            GUI::MessageBox::show(window(), "Cannot debug current project type", "Error", GUI::MessageBox::Type::Error);
-            return;
-        }
         if (!GUI::FilePicker::file_exists(get_project_executable_path())) {
             GUI::MessageBox::show(window(), String::formatted("Could not find file: {}. (did you build the project?)", get_project_executable_path()), "Error", GUI::MessageBox::Type::Error);
             return;
@@ -534,6 +510,7 @@ NonnullRefPtr<GUI::Action> HackStudioWidget::create_debug_action()
             GUI::MessageBox::show(window(), "Debugger is already running", "Error", GUI::MessageBox::Type::Error);
             return;
         }
+
         Debugger::the().set_executable_path(get_project_executable_path());
         m_debugger_thread = adopt(*new LibThread::Thread(Debugger::start_static));
         m_debugger_thread->start();
@@ -616,14 +593,15 @@ NonnullRefPtr<EditorWrapper> HackStudioWidget::get_editor_of_file(const String&
 
 String HackStudioWidget::get_project_executable_path() const
 {
-    // e.g /my/project.hsp => /my/project
+    // FIXME: Dumb heuristic ahead!
+    // e.g /my/project => /my/project/project
     // TODO: Perhaps a Makefile rule for getting the value of $(PROGRAM) would be better?
-    return m_project->path().substring(0, m_project->path().index_of(".").value());
+    return String::formatted("{}/{}", m_project->root_path(), LexicalPath(m_project->root_path()).basename());
 }
 
 void HackStudioWidget::build(TerminalWrapper& wrapper)
 {
-    if (m_project->type() == ProjectType::JavaScript && m_currently_open_file.ends_with(".js"))
+    if (m_currently_open_file.ends_with(".js"))
         wrapper.run_command(String::formatted("js -A {}", m_currently_open_file));
     else
         wrapper.run_command("make");
@@ -631,7 +609,7 @@ void HackStudioWidget::build(TerminalWrapper& wrapper)
 
 void HackStudioWidget::run(TerminalWrapper& wrapper)
 {
-    if (m_project->type() == ProjectType::JavaScript && m_currently_open_file.ends_with(".js"))
+    if (m_currently_open_file.ends_with(".js"))
         wrapper.run_command(String::formatted("js {}", m_currently_open_file));
     else
         wrapper.run_command("make run");
@@ -656,7 +634,11 @@ void HackStudioWidget::create_project_tree_view(GUI::Widget& parent)
 {
     m_project_tree_view = parent.add<GUI::TreeView>();
     m_project_tree_view->set_model(m_project->model());
-    m_project_tree_view->toggle_index(m_project_tree_view->model()->index(0, 0));
+
+    for (int column_index = 0; column_index < m_project->model().column_count(); ++column_index)
+        m_project_tree_view->set_column_hidden(column_index, true);
+
+    m_project_tree_view->set_column_hidden(GUI::FileSystemModel::Column::Name, false);
 
     m_project_tree_view->on_context_menu_request = [this](const GUI::ModelIndex& index, const GUI::ContextMenuEvent& event) {
         if (index.is_valid()) {
@@ -777,7 +759,6 @@ void HackStudioWidget::create_toolbar(GUI::Widget& parent)
 {
     auto& toolbar = parent.add<GUI::ToolBar>();
     toolbar.add_action(*m_new_action);
-    toolbar.add_action(*m_add_existing_file_action);
     toolbar.add_action(*m_save_action);
     toolbar.add_action(*m_delete_action);
     toolbar.add_separator();
@@ -837,7 +818,7 @@ void HackStudioWidget::create_action_tab(GUI::Widget& parent)
     m_terminal_wrapper = m_action_tab_widget->add_tab<TerminalWrapper>("Build", false);
     m_debug_info_widget = m_action_tab_widget->add_tab<DebugInfoWidget>("Debug");
     m_disassembly_widget = m_action_tab_widget->add_tab<DisassemblyWidget>("Disassembly");
-    m_git_widget = m_action_tab_widget->add_tab<GitWidget>("Git", LexicalPath(m_project->root_directory()));
+    m_git_widget = m_action_tab_widget->add_tab<GitWidget>("Git", LexicalPath(m_project->root_path()));
     m_git_widget->set_view_diff_callback([this](const auto& original_content, const auto& diff) {
         m_diff_viewer->set_content(original_content, diff);
         set_edit_mode(EditMode::Diff);
@@ -850,7 +831,7 @@ void HackStudioWidget::create_app_menubar(GUI::MenuBar& menubar)
     app_menu.add_action(*m_open_action);
     app_menu.add_action(*m_save_action);
     app_menu.add_separator();
-    app_menu.add_action(GUI::CommonActions::make_quit_action([this](auto&) {
+    app_menu.add_action(GUI::CommonActions::make_quit_action([](auto&) {
         GUI::Application::the()->quit();
     }));
 }
@@ -859,7 +840,6 @@ void HackStudioWidget::create_project_menubar(GUI::MenuBar& menubar)
 {
     auto& project_menu = menubar.add_menu("Project");
     project_menu.add_action(*m_new_action);
-    project_menu.add_action(*m_add_existing_file_action);
 }
 
 void HackStudioWidget::create_edit_menubar(GUI::MenuBar& menubar)
diff --git a/DevTools/HackStudio/HackStudioWidget.h b/DevTools/HackStudio/HackStudioWidget.h
index f182da1466..29ef3701e4 100644
--- a/DevTools/HackStudio/HackStudioWidget.h
+++ b/DevTools/HackStudio/HackStudioWidget.h
@@ -37,6 +37,7 @@
 #include "Git/GitWidget.h"
 #include "Locator.h"
 #include "Project.h"
+#include "ProjectFile.h"
 #include "TerminalWrapper.h"
 #include <LibGUI/ScrollBar.h>
 #include <LibGUI/Splitter.h>
@@ -67,7 +68,7 @@ private:
     static String get_full_path_of_serenity_source(const String& file);
 
     HackStudioWidget(const String& path_to_project);
-    void open_project(String filename);
+    void open_project(const String& root_path);
 
     enum class EditMode {
         Text,
@@ -80,7 +81,6 @@ private:
     NonnullRefPtr<GUI::Menu> create_project_tree_view_context_menu();
     NonnullRefPtr<GUI::Action> create_new_action();
     NonnullRefPtr<GUI::Action> create_open_selected_action();
-    NonnullRefPtr<GUI::Action> create_add_existing_file_action();
     NonnullRefPtr<GUI::Action> create_delete_action();
     NonnullRefPtr<GUI::Action> create_switch_to_next_editor_action();
     NonnullRefPtr<GUI::Action> create_switch_to_previous_editor_action();
@@ -153,7 +153,6 @@ private:
 
     RefPtr<GUI::Action> m_new_action;
     RefPtr<GUI::Action> m_open_selected_action;
-    RefPtr<GUI::Action> m_add_existing_file_action;
     RefPtr<GUI::Action> m_delete_action;
     RefPtr<GUI::Action> m_switch_to_next_editor;
     RefPtr<GUI::Action> m_switch_to_previous_editor;
diff --git a/DevTools/HackStudio/Project.cpp b/DevTools/HackStudio/Project.cpp
index 109aba8a22..2b8251bc78 100644
--- a/DevTools/HackStudio/Project.cpp
+++ b/DevTools/HackStudio/Project.cpp
@@ -26,368 +26,59 @@
 
 #include "Project.h"
 #include "HackStudio.h"
-#include <AK/LexicalPath.h>
-#include <AK/QuickSort.h>
-#include <AK/StringBuilder.h>
-#include <LibCore/DirIterator.h>
 #include <LibCore/File.h>
-#include <stdio.h>
-#include <string.h>
-#include <sys/stat.h>
-#include <unistd.h>
 
 namespace HackStudio {
 
-struct Project::ProjectTreeNode : public RefCounted<ProjectTreeNode> {
-    enum class Type {
-        Invalid,
-        Project,
-        Directory,
-        File,
-    };
-
-    ProjectTreeNode& find_or_create_subdirectory(const String& name)
-    {
-        for (auto& child : children) {
-            if (child->type == Type::Directory && child->name == name)
-                return *child;
-        }
-        auto new_child = adopt(*new ProjectTreeNode);
-        new_child->type = Type::Directory;
-        new_child->name = name;
-        new_child->parent = this;
-        auto* ptr = new_child.ptr();
-        children.append(move(new_child));
-        return *ptr;
-    }
-
-    void sort()
-    {
-        if (type == Type::File)
-            return;
-        quick_sort(children, [](auto& a, auto& b) {
-            return a->name < b->name;
-        });
-        for (auto& child : children)
-            child->sort();
-    }
-
-    Type type { Type::Invalid };
-    String name;
-    String path;
-    Vector<NonnullRefPtr<ProjectTreeNode>> children;
-    ProjectTreeNode* parent { nullptr };
-};
-
-class ProjectModel final : public GUI::Model {
-public:
-    explicit ProjectModel(Project& project)
-        : m_project(project)
-    {
-    }
-
-    virtual int row_count(const GUI::ModelIndex& index) const override
-    {
-        if (!index.is_valid())
-            return 1;
-        auto* node = static_cast<Project::ProjectTreeNode*>(index.internal_data());
-        return node->children.size();
-    }
-
-    virtual int column_count(const GUI::ModelIndex&) const override
-    {
-        return 1;
-    }
-
-    virtual GUI::Variant data(const GUI::ModelIndex& index, GUI::ModelRole role) const override
-    {
-        auto* node = static_cast<Project::ProjectTreeNode*>(index.internal_data());
-        if (role == GUI::ModelRole::Display) {
-            return node->name;
-        }
-        if (role == GUI::ModelRole::Custom) {
-            return node->path;
-        }
-        if (role == GUI::ModelRole::Icon) {
-            if (node->type == Project::ProjectTreeNode::Type::Project)
-                return m_project.m_project_icon;
-            if (node->type == Project::ProjectTreeNode::Type::Directory)
-                return m_project.m_directory_icon;
-            if (node->name.ends_with(".cpp"))
-                return m_project.m_cplusplus_icon;
-            if (node->name.ends_with(".frm"))
-                return m_project.m_form_icon;
-            if (node->name.ends_with(".h"))
-                return m_project.m_header_icon;
-            if (node->name.ends_with(".hsp"))
-                return m_project.m_hackstudio_icon;
-            if (node->name.ends_with(".js"))
-                return m_project.m_javascript_icon;
-            return m_project.m_file_icon;
-        }
-        if (role == GUI::ModelRole::Font) {
-            if (node->name == currently_open_file())
-                return Gfx::Font::default_bold_font();
-            return {};
-        }
-        return {};
-    }
-
-    virtual GUI::ModelIndex index(int row, int column = 0, const GUI::ModelIndex& parent = GUI::ModelIndex()) const override
-    {
-        if (!parent.is_valid()) {
-            return create_index(row, column, &m_project.root_node());
-        }
-        auto& node = *static_cast<Project::ProjectTreeNode*>(parent.internal_data());
-        return create_index(row, column, node.children.at(row).ptr());
-    }
-
-    GUI::ModelIndex parent_index(const GUI::ModelIndex& index) const override
-    {
-        if (!index.is_valid())
-            return {};
-        auto& node = *static_cast<Project::ProjectTreeNode*>(index.internal_data());
-        if (!node.parent)
-            return {};
-
-        if (!node.parent->parent) {
-            return create_index(0, 0, &m_project.root_node());
-            ASSERT_NOT_REACHED();
-            return {};
-        }
-
-        for (size_t row = 0; row < node.parent->parent->children.size(); ++row) {
-            if (node.parent->parent->children[row].ptr() == node.parent)
-                return create_index(row, 0, node.parent);
-        }
-
-        ASSERT_NOT_REACHED();
-        return {};
-    }
-
-    virtual void update() override
-    {
-        did_update();
-    }
-
-private:
-    Project& m_project;
-};
-
-Project::Project(const String& path, Vector<String>&& filenames)
-    : m_path(path)
+Project::Project(const String& root_path)
+    : m_root_path(root_path)
 {
-    m_name = LexicalPath(m_path).basename();
-
-    m_file_icon = GUI::Icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/filetype-unknown.png"));
-    m_cplusplus_icon = GUI::Icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/filetype-cplusplus.png"));
-    m_header_icon = GUI::Icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/filetype-header.png"));
-    m_directory_icon = GUI::Icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/filetype-folder.png"));
-    m_project_icon = GUI::Icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/hackstudio-project.png"));
-    m_javascript_icon = GUI::Icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/filetype-javascript.png"));
-    m_hackstudio_icon = GUI::Icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/filetype-hackstudio.png"));
-    m_form_icon = GUI::Icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/filetype-form.png"));
-
-    for (auto& filename : filenames) {
-        m_files.append(ProjectFile::construct_with_name(filename));
-    }
-
-    m_model = adopt(*new ProjectModel(*this));
-
-    rebuild_tree();
+    m_model = GUI::FileSystemModel::create(root_path, GUI::FileSystemModel::Mode::FilesAndDirectories);
 }
 
 Project::~Project()
 {
 }
 
-OwnPtr<Project> Project::load_from_file(const String& path)
+OwnPtr<Project> Project::open_with_root_path(const String& root_path)
 {
-    auto file = Core::File::construct(path);
-    if (!file->open(Core::File::ReadOnly))
+    if (!Core::File::is_directory(root_path))
         return nullptr;
-
-    auto type = ProjectType::Cpp;
-    Vector<String> files;
-
-    auto add_glob = [&](String path) {
-        auto split = path.split('*', true);
-        for (auto& item : split) {
-            dbg() << item;
-        }
-        ASSERT(split.size() == 2);
-        auto cwd = getcwd(nullptr, 0);
-        Core::DirIterator it(cwd, Core::DirIterator::Flags::SkipParentAndBaseDir);
-        while (it.has_next()) {
-            auto path = it.next_path();
-            if (!split[0].is_empty() && !path.starts_with(split[0]))
-                continue;
-
-            if (!split[1].is_empty() && !path.ends_with(split[1]))
-                continue;
-
-            files.append(path);
-        }
-    };
-
-    for (;;) {
-        auto line = file->read_line(1024);
-        if (line.is_null())
-            break;
-
-        auto path = String::copy(line, Chomp);
-        if (path.contains("*"))
-            add_glob(path);
-        else
-            files.append(path);
-    }
-
-    for (auto& file : files) {
-        if (file.ends_with(".js")) {
-            type = ProjectType::JavaScript;
-            break;
-        }
-    }
-
-    quick_sort(files);
-
-    auto project = adopt_own(*new Project(path, move(files)));
-    project->m_type = type;
-    return project;
+    return adopt_own(*new Project(root_path));
 }
 
-bool Project::add_file(const String& filename)
+template<typename Callback>
+static void traverse_model(const GUI::FileSystemModel& model, const GUI::ModelIndex& index, Callback callback)
 {
-    m_files.append(ProjectFile::construct_with_name(filename));
-    rebuild_tree();
-    m_model->update();
-    return save();
-}
-
-bool Project::remove_file(const String& filename)
-{
-    if (!get_file(filename))
-        return false;
-    m_files.remove_first_matching([filename](auto& file) { return file->name() == filename; });
-    rebuild_tree();
-    m_model->update();
-    return save();
-}
-
-bool Project::save()
-{
-    auto project_file = Core::File::construct(m_path);
-    if (!project_file->open(Core::File::WriteOnly))
-        return false;
-
-    for (auto& file : m_files) {
-        // FIXME: Check for error here. IODevice::printf() needs some work on error reporting.
-        project_file->printf("%s\n", file.name().characters());
+    if (index.is_valid())
+        callback(index);
+    auto row_count = model.row_count(index);
+    if (!row_count)
+        return;
+    for (int row = 0; row < row_count; ++row) {
+        auto child_index = model.index(row, GUI::FileSystemModel::Column::Name, index);
+        traverse_model(model, child_index, callback);
     }
-
-    if (!project_file->close())
-        return false;
-
-    return true;
 }
 
-RefPtr<ProjectFile> Project::get_file(const String& filename)
+void Project::for_each_text_file(Function<void(const ProjectFile&)> callback) const
 {
-    for (auto& file : m_files) {
-        if (LexicalPath(file.name()).string() == LexicalPath(filename).string())
-            return &file;
-    }
-    return nullptr;
-}
-
-String Project::default_file() const
-{
-    if (m_files.size() > 0) {
-        if (m_type != ProjectType::Unknown) {
-            StringView extension;
-            switch (m_type) {
-            case ProjectType::Cpp:
-                extension = ".cpp";
-                break;
-            case ProjectType::JavaScript:
-                extension = ".js";
-                break;
-            default:
-                ASSERT_NOT_REACHED();
-            }
-
-            auto project_file = m_files.find([&](auto project_file) {
-                return project_file->name().ends_with(extension);
-            });
-
-            if (!project_file.is_end()) {
-                auto& file = *project_file;
-                return file->name();
-            }
-        }
-
-        return m_files.first().name();
-    }
-
-    ASSERT_NOT_REACHED();
+    traverse_model(model(), {}, [&](auto& index) {
+        auto file = get_file(model().full_path(index));
+        if (file)
+            callback(*file);
+    });
 }
 
-void Project::rebuild_tree()
+RefPtr<ProjectFile> Project::get_file(const String& path) const
 {
-    auto root = adopt(*new ProjectTreeNode);
-    root->name = m_name;
-    root->type = ProjectTreeNode::Type::Project;
-
     for (auto& file : m_files) {
-        LexicalPath path(file.name());
-        ProjectTreeNode* current = root.ptr();
-        StringBuilder partial_path;
-
-        for (size_t i = 0; i < path.parts().size(); ++i) {
-            auto& part = path.parts().at(i);
-            if (part == ".")
-                continue;
-            if (i != path.parts().size() - 1) {
-                current = &current->find_or_create_subdirectory(part);
-                continue;
-            }
-            struct stat st;
-            if (lstat(path.string().characters(), &st) == 0) {
-                if (S_ISDIR(st.st_mode)) {
-                    current = &current->find_or_create_subdirectory(part);
-                    continue;
-                }
-            }
-            auto file_node = adopt(*new ProjectTreeNode);
-            file_node->name = part;
-            file_node->path = path.string();
-            file_node->type = Project::ProjectTreeNode::Type::File;
-            file_node->parent = current;
-            current->children.append(move(file_node));
-            break;
-        }
+        if (file.name() == path)
+            return file;
     }
-
-    root->sort();
-
-#if 0
-    Function<void(ProjectTreeNode&, int indent)> dump_tree = [&](ProjectTreeNode& node, int indent) {
-        for (int i = 0; i < indent; ++i)
-            out(" ");
-        if (node.name.is_null())
-            outln("(null)");
-        else
-            outln("{}", node.name);
-        for (auto& child : node.children) {
-            dump_tree(*child, indent + 2);
-        }
-    };
-
-    dump_tree(*root, 0);
-#endif
-
-    m_root_node = move(root);
-    m_model->update();
+    auto file = ProjectFile::construct_with_name(path);
+    m_files.append(file);
+    return file;
 }
 
 }
diff --git a/DevTools/HackStudio/Project.h b/DevTools/HackStudio/Project.h
index dddb34726f..6d3453e84e 100644
--- a/DevTools/HackStudio/Project.h
+++ b/DevTools/HackStudio/Project.h
@@ -29,19 +29,11 @@
 #include "ProjectFile.h"
 #include <AK/LexicalPath.h>
 #include <AK/Noncopyable.h>
-#include <AK/NonnullRefPtrVector.h>
 #include <AK/OwnPtr.h>
-#include <LibGUI/Icon.h>
-#include <LibGUI/Model.h>
+#include <LibGUI/FileSystemModel.h>
 
 namespace HackStudio {
 
-enum class ProjectType {
-    Unknown,
-    Cpp,
-    JavaScript
-};
-
 class Project {
     AK_MAKE_NONCOPYABLE(Project);
     AK_MAKE_NONMOVABLE(Project);
@@ -49,52 +41,24 @@ class Project {
 public:
     ~Project();
 
-    static OwnPtr<Project> load_from_file(const String& path);
+    static OwnPtr<Project> open_with_root_path(const String& root_path);
 
-    [[nodiscard]] bool add_file(const String& filename);
-    [[nodiscard]] bool remove_file(const String& filename);
-    [[nodiscard]] bool save();
+    GUI::FileSystemModel& model() { return *m_model; }
+    const GUI::FileSystemModel& model() const { return *m_model; }
+    String name() const { return LexicalPath(m_root_path).basename(); }
+    String root_path() const { return m_root_path; }
 
-    RefPtr<ProjectFile> get_file(const String& filename);
+    RefPtr<ProjectFile> get_file(const String& path) const;
 
-    ProjectType type() const { return m_type; }
-    GUI::Model& model() { return *m_model; }
-    String default_file() const;
-    String name() const { return m_name; }
-    String path() const { return m_path; }
-    String root_directory() const { return LexicalPath(m_path).dirname(); }
-
-    template<typename Callback>
-    void for_each_text_file(Callback callback) const
-    {
-        for (auto& file : m_files) {
-            callback(file);
-        }
-    }
+    void for_each_text_file(Function<void(const ProjectFile&)>) const;
 
 private:
-    friend class ProjectModel;
-    struct ProjectTreeNode;
-    explicit Project(const String& path, Vector<String>&& files);
-
-    const ProjectTreeNode& root_node() const { return *m_root_node; }
-    void rebuild_tree();
+    explicit Project(const String& root_path);
 
-    ProjectType m_type { ProjectType::Unknown };
-    String m_name;
-    String m_path;
-    RefPtr<GUI::Model> m_model;
-    NonnullRefPtrVector<ProjectFile> m_files;
-    RefPtr<ProjectTreeNode> m_root_node;
+    RefPtr<GUI::FileSystemModel> m_model;
+    mutable NonnullRefPtrVector<ProjectFile> m_files;
 
-    GUI::Icon m_directory_icon;
-    GUI::Icon m_file_icon;
-    GUI::Icon m_cplusplus_icon;
-    GUI::Icon m_header_icon;
-    GUI::Icon m_project_icon;
-    GUI::Icon m_javascript_icon;
-    GUI::Icon m_hackstudio_icon;
-    GUI::Icon m_form_icon;
+    String m_root_path;
 };
 
 }
diff --git a/DevTools/HackStudio/main.cpp b/DevTools/HackStudio/main.cpp
index 7cad913aef..c6e1db8854 100644
--- a/DevTools/HackStudio/main.cpp
+++ b/DevTools/HackStudio/main.cpp
@@ -54,8 +54,6 @@ static RefPtr<HackStudioWidget> s_hack_studio_widget;
 
 static bool make_is_available();
 static void update_path_environment_variable();
-static String path_to_project(const String& path_argument_absolute_path);
-static void open_default_project_file(const String& project_path);
 
 int main(int argc, char** argv)
 {
@@ -73,7 +71,6 @@ int main(int argc, char** argv)
 
     s_window = GUI::Window::construct();
     s_window->resize(840, 600);
-    s_window->set_title("HackStudio");
     s_window->set_icon(Gfx::Bitmap::load_from_file("/res/icons/16x16/app-hack-studio.png"));
 
     update_path_environment_variable();
@@ -88,16 +85,20 @@ int main(int argc, char** argv)
 
     auto argument_absolute_path = Core::File::real_path_for(path_argument);
 
-    auto menubar = GUI::MenuBar::construct();
-    auto project_path = path_to_project(argument_absolute_path);
+    auto project_path = argument_absolute_path;
+    if (argument_absolute_path.is_null())
+        project_path = Core::File::real_path_for(".");
+
     s_hack_studio_widget = s_window->set_main_widget<HackStudioWidget>(project_path);
 
+    s_window->set_title(String::formatted("{} - HackStudio", s_hack_studio_widget->project().name()));
+
+    auto menubar = GUI::MenuBar::construct();
     s_hack_studio_widget->initialize_menubar(menubar);
     app->set_menubar(menubar);
 
     s_window->show();
 
-    open_default_project_file(argument_absolute_path);
     s_hack_studio_widget->update_actions();
 
     return app->exec();
@@ -131,22 +132,6 @@ static void update_path_environment_variable()
     setenv("PATH", path.to_string().characters(), true);
 }
 
-static String path_to_project(const String& path_argument_absolute_path)
-{
-    if (path_argument_absolute_path.ends_with(".hsp"))
-        return path_argument_absolute_path;
-    else
-        return "/home/anon/Source/little/little.hsp";
-}
-
-static void open_default_project_file(const String& project_path)
-{
-    if (!project_path.is_empty() && !project_path.ends_with(".hsp"))
-        open_file(project_path);
-    else
-        open_file(s_hack_studio_widget->project().default_file());
-}
-
 namespace HackStudio {
 
 GUI::TextEditor& current_editor()