Implement basic multithreading support

A few CPU heavy operations, which are opening an archive and displaying
a selected Activity, have been moved to another thread to avoid having
long-running operations on the main thread.

6 files changed, 51 insertions, 14 deletions

diff --git a/src/archive_parser.cpp b/src/archive_parser.cpp
index 77d3ec0..96df1ec 100644
--- a/src/archive_parser.cpp
+++ b/src/archive_parser.cpp
@@ -19,7 +19,7 @@
 Archive::Archive(QString outbox_filename, ArchiveType archive_type) :
     outbox_filename(outbox_filename), archive_type(archive_type) {}
 
-Archive::InitError Archive::init() {
+std::variant<QString, Archive::InitError> Archive::init() {
     QFile outbox_file(outbox_filename);
 
     if (!outbox_file.open(QIODevice::ReadOnly | QIODevice::Text))
@@ -233,7 +233,7 @@ std::vector<APAttachmentFields> Archive::get_status_attachments_list(QJsonValueR
 }
 
 // status_index is assumed to be a valid index
-QString Archive::get_html_status_info(int status_index, int text_zone_width, StatusType status_type, QLocale* locale) {
+const QString Archive::get_html_status_info(int status_index, int text_zone_width, StatusType status_type, QLocale* locale) {
     // the JSON AP Activity (TODO: fix misleading name)
     QJsonObject obj = outbox_items->at(status_index).toObject();
 
@@ -303,7 +303,7 @@ QString Archive::get_html_status_info(int status_index, int text_zone_width, Sta
 }
 
 // TODO: make this use an APActivity object that will be present as an StatusListItem member.
-QString Archive::get_html_status_text(int status_index) {
+const QString Archive::get_html_status_text(int status_index) {
     QString text("");
     QJsonObject obj = outbox_items->at(status_index).toObject();
 
diff --git a/src/archive_parser.h b/src/archive_parser.h
index c206087..7377120 100644
--- a/src/archive_parser.h
+++ b/src/archive_parser.h
@@ -28,11 +28,11 @@ public:
 
     Archive(QString outbox_filename, ArchiveType archive_type);
     ~Archive();
-    InitError init();
+    std::variant<QString, InitError> init();
 
     void update_status_list(ViewStatusTypes allowed_types, QListWidget *parent);
-    QString get_html_status_info(int status_index, int text_zone_width, StatusType status_type, QLocale* locale);
-    QString get_html_status_text(int status_index);
+    const QString get_html_status_info(int status_index, int text_zone_width, StatusType status_type, QLocale* locale);
+    const QString get_html_status_text(int status_index);
 private:
     QString outbox_filename;
     QDir archive_root_dir;
diff --git a/src/list_item.cpp b/src/list_item.cpp
index c74fa39..020ccde 100644
--- a/src/list_item.cpp
+++ b/src/list_item.cpp
@@ -39,6 +39,6 @@ StatusType StatusListItem::get_status_type() {
     return status_type;
 }
 
-QString StatusListItem::get_info_html(int text_zone_width, QLocale* locale) {
+const QString StatusListItem::get_info_html(int text_zone_width, QLocale* locale) {
     return data_archive->get_html_status_info(status_index, text_zone_width, status_type, locale);
 }
diff --git a/src/list_item.h b/src/list_item.h
index 9ca0aac..4514903 100644
--- a/src/list_item.h
+++ b/src/list_item.h
@@ -13,7 +13,7 @@ public:
     StatusListItem(const QString &text, StatusType status_type, bool has_attachement, Archive* data_archive, QListWidget *parent = nullptr, int index = 0);
     int get_status_index();
     StatusType get_status_type();
-    QString get_info_html(int text_zone_width, QLocale* locale);
+    const QString get_info_html(int text_zone_width, QLocale* locale);
 
 private:
     int status_index;
diff --git a/src/mainwindow.cpp b/src/mainwindow.cpp
index ede24f8..363f2b1 100644
--- a/src/mainwindow.cpp
+++ b/src/mainwindow.cpp
@@ -9,6 +9,7 @@
 #include <QRandomGenerator>
 #include <QClipboard>
 #include <QMimeData>
+#include <QtConcurrent/QtConcurrent>
 
 MainWindow::MainWindow(QWidget *parent)
     : QMainWindow(parent)
@@ -17,6 +18,7 @@ MainWindow::MainWindow(QWidget *parent)
     ui->setupUi(this);
     connect(ui->buttonCopy, &QPushButton::clicked, ui->actionCopy_status, &QAction::trigger);
     connect(ui->buttonRandom, &QPushButton::clicked, ui->actionRandom_status, &QAction::trigger);
+    connect(&archive_thread_watcher, &QFutureWatcher<std::variant<QString, Archive::InitError>>::finished, this, &MainWindow::archive_thread_watcher_done);
 }
 
 MainWindow::~MainWindow()
@@ -60,15 +62,22 @@ void MainWindow::on_actionAbout_triggered(bool checked) {
     QMessageBox::information(this, "title", "text");
 }
 
+std::variant<QString, Archive::InitError> start_listWidget_itemActivated(StatusListItem* status, int text_zone_width, QLocale* locale) {
+    return (QString)status->get_info_html(text_zone_width, locale);
+}
+
 void MainWindow::on_listWidget_itemActivated(QListWidgetItem *item) {
     StatusListItem* status = dynamic_cast<StatusListItem*>(item);
     if (status != nullptr) {
-        // TODO: do this in another thread
-        QString status_info = status->get_info_html(ui->statusInfoText->width(), &locale_context);
-        ui->statusInfoText->setHtml(status_info);
+        const QFuture<std::variant<QString, Archive::InitError>> status_info = QtConcurrent::run(start_listWidget_itemActivated, status, ui->statusInfoText->width(), &locale_context);
+        archive_thread_watcher.setFuture(status_info);
     }
 }
 
+void MainWindow::finish_listWidget_itemActivated(const QString& status_info) {
+    ui->statusInfoText->setHtml(status_info);
+}
+
 void MainWindow::on_actionRandom_status_triggered(bool checked) {
     if (data_archive == nullptr) return; // No archive open, avoids crashing
 
@@ -201,14 +210,19 @@ void MainWindow::open_file(const QString &filename) {
         data_archive = nullptr;
     }
 
-    // TODO: Do this in another thread
+    open_file_filename = filename;
+
     QApplication::setOverrideCursor(Qt::WaitCursor);
     data_archive = new Archive(filename, ArchiveType::MASTODON);
-    auto parse_error = data_archive->init();
 
+    QFuture<std::variant<QString, Archive::InitError>> parse_error = QtConcurrent::run(data_archive, &Archive::init);
+    archive_thread_watcher.setFuture(parse_error);
+}
+
+void MainWindow::finish_open_file(const Archive::InitError& parse_error) {
     switch (parse_error) {
         case Archive::FailedOpeningFile:
-            QMessageBox::warning(this, tr("Archive Parser"), tr("Failed opening file %1").arg(filename)); break;
+            QMessageBox::warning(this, tr("Archive Parser"), tr("Failed opening file %1").arg(open_file_filename)); break;
         case Archive::JsonParseError:
             QMessageBox::warning(this, tr("Archive Parser"), tr("Failed parsing outbox JSON.")); break;
         case Archive::JsonEmpty:
@@ -228,3 +242,17 @@ void MainWindow::open_file(const QString &filename) {
 
     QApplication::restoreOverrideCursor();
 }
+
+void MainWindow::archive_thread_watcher_done() {
+    std::variant<QString, Archive::InitError> result = archive_thread_watcher.result();
+
+    // For MainWindow::on_listWidget_itemActivated
+    if (const QString* status_info = std::get_if<QString>(&result)) {
+        finish_listWidget_itemActivated(*status_info);
+    } else
+    // For MainWindow::open_file
+    if (const Archive::InitError* parse_error = std::get_if<Archive::InitError>(&result)) {
+        finish_open_file(*parse_error);
+    } else
+        qDebug() << "What, the variant is weird";
+}
diff --git a/src/mainwindow.h b/src/mainwindow.h
index f1de2d7..abf9acc 100644
--- a/src/mainwindow.h
+++ b/src/mainwindow.h
@@ -3,6 +3,8 @@
 #include <QMainWindow>
 #include <QListWidgetItem>
 #include <QLocale>
+#include <QFutureWatcher>
+#include <variant>
 
 #include "archive_parser.h"
 #include "types.h"
@@ -47,6 +49,12 @@ private:
     void reset_view_filters();
     void relist_statuses();
     void open_file(const QString &filename);
+    void archive_thread_watcher_done();
+
+    void finish_listWidget_itemActivated(const QString& status_info);
+    void finish_open_file(const Archive::InitError& parse_error);
+
+    QString open_file_filename;
 
     Ui::MainWindow *ui;
 
@@ -54,6 +62,7 @@ private:
     bool view_filters_changed = false;
 
     Archive *data_archive = nullptr;
+    QFutureWatcher<std::variant<QString, Archive::InitError>> archive_thread_watcher;
 
     QLocale locale_context;
 };