path: root/src/mainwindow.cpp

/*
 * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
 * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include "mainwindow.h"

#include <QAction>
#include <QComboBox>
#include <QDialog>
#include <QDialogButtonBox>
#include <QHBoxLayout>
#include <QHeaderView>
#include <QLabel>
#include <QLineEdit>
#include <QMenu>
#include <QMenuBar>
#include <QMessageBox>
#include <QPlainTextEdit>
#include <QPushButton>
#include <QSettings>
#include <QSplitter>
#include <QStatusBar>
#include <QTableView>
#include <QToolBar>
#include <QVBoxLayout>

#include "mailsync.h"
#include "messageview.h"
#include "mimeparser.h"
#include "notmuchworker.h"
#include "tagchip.h"
#include "threadlistmodel.h"
#include "version.h"

QStringList MainWindow::registeredActionNames() const
{
    // Derived from the actions themselves, so it cannot drift from what
    // registerActions() really installed.
    QStringList names = m_actions.keys();
    names.sort();
    return names;
}

QString MainWindow::cidPrefixForIndex(int index)
{
    // "m<index>" is digits only after the 'm', so it cannot contain '!'.
    return QStringLiteral("m%1").arg(index);
}

MainWindow::MainWindow(const Config &config, QWidget *parent)
    : QMainWindow(parent), m_config(config)
{
    qRegisterMetaType<ThreadSummary>();
    qRegisterMetaType<MessageRef>();
    qRegisterMetaType<TagChange>();
    qRegisterMetaType<QVector<ThreadSummary>>();
    qRegisterMetaType<QVector<MessageRef>>();

    m_keyMap.loadDefaults();
    {
        QSettings settings(Config::defaultPath(), QSettings::IniFormat);
        m_keyMap.loadOverrides(settings);
        m_tagColors.load(settings);
    }

    // An account's chip colour comes from its own stanza, since an account tag
    // is a different taxonomy from a functional one.
    for (const Account &account : m_config.accounts()) {
        m_tagColors.setAccountColour(account.key, account.color);
        m_tagColors.setAccountLabel(account.key, account.label);
    }

    buildUi();
    registerActions();
    buildMenus();
    wireWorker();
    showWarnings();

    // No event filter: QAction shortcuts are dispatched before the focused
    // widget sees the key, so they beat QAbstractItemView's type-to-search
    // without one. Qt also suppresses a plain-letter shortcut while an
    // editable widget has focus, so typing in the query bar stays typing;
    // modifier shortcuts such as Ctrl+Q still work there, which the old
    // filter blocked.

    if (!m_config.savedQueries().isEmpty()) {
        m_queryEdit->setText(m_config.savedQueries().first().query);
        runCurrentQuery();
    }
}

MainWindow::~MainWindow()
{
    m_workerThread.quit();
    m_workerThread.wait();
}

void MainWindow::buildUi()
{
    auto *central = new QWidget(this);
    auto *layout = new QVBoxLayout(central);

    // The status label is created first: the sync wiring below can report into
    // it before the rest of the UI exists.
    m_statusLabel = new QLabel(this);
    statusBar()->addWidget(m_statusLabel);

    // Query row.
    auto *queryRow = new QHBoxLayout;
    m_accountBox = new QComboBox(central);
    m_accountBox->addItem(tr("All accounts"), QString());
    for (const Account &account : m_config.accounts())
        m_accountBox->addItem(account.key, account.key);

    m_queryEdit = new QLineEdit(central);
    m_queryEdit->setPlaceholderText(tr("notmuch query, e.g. tag:inbox"));
    connect(m_queryEdit, &QLineEdit::returnPressed,
            this, &MainWindow::runCurrentQuery);

    m_syncLog = new QPlainTextEdit(central);
    m_syncLog->setReadOnly(true);
    m_syncLog->setMaximumHeight(120);
    m_syncLog->hide();

    m_syncButton = new QPushButton(tr("Sync"), central);
    m_sync = new MailSync(m_config.syncCommand(), this);
    m_syncButton->setEnabled(m_sync->isAvailable());
    if (!m_sync->isAvailable()) {
        m_syncButton->setToolTip(
            tr("No sync command configured ([sync] command in qtmaildir.conf)"));
    }
    connect(m_syncButton, &QPushButton::clicked, this, [this]() {
        if (!m_sync->start())
            m_statusLabel->setText(tr("Sync already running"));
    });
    connect(m_sync, &MailSync::finished, this, &MainWindow::onSyncFinished);
    connect(m_sync, &MailSync::outputReceived, this, [this](const QString &chunk) {
        m_syncLog->appendPlainText(chunk.trimmed());
    });

    queryRow->addWidget(m_accountBox);
    queryRow->addWidget(m_queryEdit, 1);
    queryRow->addWidget(m_syncButton);
    layout->addLayout(queryRow);

    // Saved query buttons.
    auto *savedRow = new QHBoxLayout;
    for (const SavedQuery &saved : m_config.savedQueries()) {
        auto *button = new QPushButton(saved.name, central);
        connect(button, &QPushButton::clicked, this, [this, saved]() {
            m_queryEdit->setText(saved.query);
            runCurrentQuery();
        });
        savedRow->addWidget(button);
    }
    savedRow->addStretch();
    layout->addLayout(savedRow);

    // Thread list and message pane.
    m_model = new ThreadListModel(this);
    m_model->setTagColors(&m_tagColors);
    m_threadView = new QTableView(central);
    m_threadView->setModel(m_model);
    m_threadView->setSelectionBehavior(QAbstractItemView::SelectRows);
    m_threadView->setSelectionMode(QAbstractItemView::ExtendedSelection);
    m_threadView->verticalHeader()->hide();
    m_threadView->horizontalHeader()->setStretchLastSection(false);
    // Every column Interactive, Subject included: Stretch and ResizeToContents
    // both compute a width and discard the user's drag. Nothing absorbs spare
    // width as a result, so the columns end where they end.
    for (int column = 0; column < ThreadListModel::ColumnCount; ++column) {
        m_threadView->horizontalHeader()->setSectionResizeMode(
            column, QHeaderView::Interactive);
    }

    // The subject cell carries the account chip in front of its text.
    m_threadView->setItemDelegateForColumn(ThreadListModel::SubjectColumn,
                                           new SubjectDelegate(this));
    // Widening a column past the viewport scrolls rather than squeezing the
    // others. Per-pixel so the scroll does not jump a whole column at a time.
    m_threadView->setHorizontalScrollBarPolicy(Qt::ScrollBarAsNeeded);
    m_threadView->setHorizontalScrollMode(QAbstractItemView::ScrollPerPixel);

    // Starting widths only; a drag overrides them, and they are what the
    // saved-widths item will persist.
    m_threadView->setColumnWidth(ThreadListModel::DateColumn, 130);
    m_threadView->setColumnWidth(ThreadListModel::AuthorsColumn, 180);
    m_threadView->setColumnWidth(ThreadListModel::SubjectColumn, 520);

    connect(m_threadView->selectionModel(),
            &QItemSelectionModel::currentRowChanged,
            this, &MainWindow::onThreadSelected);

    m_messageView = new MessageView(central);
    m_messageView->setTagColors(&m_tagColors);
    connect(m_messageView, &MessageView::statusMessage,
            this, [this](const QString &text) { m_statusLabel->setText(text); });

    auto *splitter = new QSplitter(Qt::Horizontal, central);
    splitter->addWidget(m_threadView);
    splitter->addWidget(m_messageView);
    splitter->setStretchFactor(1, 2);
    layout->addWidget(splitter, 1);

    layout->addWidget(m_syncLog);

    setCentralWidget(central);

    resize(1200, 800);
    setWindowTitle(QStringLiteral("qtmaildir %1").arg(QTMAILDIR_VERSION));
}

QAction *MainWindow::addAction(const QString &name, const QString &text,
                               const QString &description,
                               const std::function<void()> &handler)
{
    auto *action = new QAction(text, this);
    action->setObjectName(name);
    action->setStatusTip(description);
    m_actionDescriptions.insert(name, description);

    // The binding comes from KeyMap, so a [keys] override reaches the menus
    // and the shortcut reference as well as the keyboard.
    const QKeySequence sequence = m_keyMap.sequenceFor(name);
    if (!sequence.isEmpty())
        action->setShortcut(sequence);

    // Shortcuts must work while focus is in the thread list or the message
    // view, not only on the window itself.
    action->setShortcutContext(Qt::WindowShortcut);

    connect(action, &QAction::triggered, this, handler);

    // Added to the window so the shortcut is live even before the action is
    // put in a menu; the ones that never reach a menu depend on this.
    QMainWindow::addAction(action);
    m_actions.insert(name, action);
    return action;
}

void MainWindow::registerActions()
{
    addAction(QStringLiteral("focus_query"), tr("&Find"),
              tr("Focus and select the query bar"), [this]() {
        m_queryEdit->setFocus();
        m_queryEdit->selectAll();
    });
    addAction(QStringLiteral("next_thread"), tr("&Next thread"),
              tr("Select the next thread"), [this]() {
        const QModelIndex current = m_threadView->currentIndex();
        const int row = current.isValid() ? current.row() + 1 : 0;
        if (row < m_model->rowCount())
            m_threadView->selectRow(row);
    });
    addAction(QStringLiteral("prev_thread"), tr("&Previous thread"),
              tr("Select the previous thread"), [this]() {
        const QModelIndex current = m_threadView->currentIndex();
        if (current.isValid() && current.row() > 0)
            m_threadView->selectRow(current.row() - 1);
    });
    addAction(QStringLiteral("open_thread"), tr("&Open thread"),
              tr("Focus the thread list"), [this]() {
        m_threadView->setFocus();
    });
    addAction(QStringLiteral("archive"), tr("&Archive"),
              tr("Remove inbox from every selected thread"), [this]() {
        tagSelected({}, { QStringLiteral("inbox") }, tr("Archive"));
    });
    addAction(QStringLiteral("delete"), tr("&Delete"),
              tr("Add the deleted tag"), [this]() {
        tagSelected({ QStringLiteral("deleted") }, {}, tr("Delete"));
    });
    addAction(QStringLiteral("spam"), tr("Mark &spam"),
              tr("Add spam and remove inbox"), [this]() {
        tagSelected({ QStringLiteral("spam") }, { QStringLiteral("inbox") },
                    tr("Mark spam"));
    });
    addAction(QStringLiteral("flag"), tr("&Flag"),
              tr("Add the flagged tag"), [this]() {
        tagSelected({ QStringLiteral("flagged") }, {}, tr("Flag"));
    });
    addAction(QStringLiteral("toggle_unread"), tr("Toggle &unread"),
              tr("Toggle the unread tag"), [this]() {
        // The direction comes from the current row, but the change applies to
        // the whole selection, so a mixed selection lands in one consistent
        // state rather than each row flipping its own way.
        const QModelIndex current = m_threadView->currentIndex();
        if (!current.isValid())
            return;
        const ThreadSummary thread = m_model->threadAt(current.row());
        if (thread.isUnread())
            tagSelected({}, { QStringLiteral("unread") }, tr("Mark read"));
        else
            tagSelected({ QStringLiteral("unread") }, {}, tr("Mark unread"));
    });
    addAction(QStringLiteral("toggle_html"), tr("Toggle &HTML"),
              tr("Switch the thread between HTML and plain text"), [this]() {
        m_messageView->toggleHtml();
    });
    addAction(QStringLiteral("load_remote"), tr("Load &remote content"),
              tr("Load remote images for the current thread"), [this]() {
        m_messageView->loadRemoteContent();
    });
    addAction(QStringLiteral("undo"), tr("&Undo"),
              tr("Undo the last tag change"), [this]() {
        if (m_undoStack.canUndo())
            m_undoStack.undo();
        else
            m_statusLabel->setText(tr("Nothing to undo"));
    });
    addAction(QStringLiteral("sync"), tr("&Sync"),
              tr("Run the configured sync command"), [this]() {
        if (m_sync->isAvailable())
            m_sync->start();
    });
    addAction(QStringLiteral("quit"), tr("&Quit"),
              tr("Quit qtmaildir"), [this]() { close(); });

    // A binding the user wrote for an action that does not exist would be
    // silently dead. KeyMap warns about unknown names, but only a check here
    // catches the reverse: a known action nothing implements.
    Q_ASSERT(m_actions.size() == KeyMap::knownActions().size());
}

void MainWindow::buildMenus()
{
    auto *fileMenu = menuBar()->addMenu(tr("&File"));
    fileMenu->addAction(m_actions.value(QStringLiteral("sync")));
    fileMenu->addSeparator();
    fileMenu->addAction(m_actions.value(QStringLiteral("quit")));

    auto *editMenu = menuBar()->addMenu(tr("&Edit"));
    editMenu->addAction(m_actions.value(QStringLiteral("undo")));
    editMenu->addSeparator();
    editMenu->addAction(m_actions.value(QStringLiteral("focus_query")));

    auto *messageMenu = menuBar()->addMenu(tr("&Message"));
    messageMenu->addAction(m_actions.value(QStringLiteral("archive")));
    messageMenu->addAction(m_actions.value(QStringLiteral("delete")));
    messageMenu->addAction(m_actions.value(QStringLiteral("spam")));
    messageMenu->addSeparator();
    messageMenu->addAction(m_actions.value(QStringLiteral("toggle_unread")));
    messageMenu->addAction(m_actions.value(QStringLiteral("flag")));

    auto *viewMenu = menuBar()->addMenu(tr("&View"));
    viewMenu->addAction(m_actions.value(QStringLiteral("prev_thread")));
    viewMenu->addAction(m_actions.value(QStringLiteral("next_thread")));
    viewMenu->addSeparator();
    viewMenu->addAction(m_actions.value(QStringLiteral("toggle_html")));
    viewMenu->addAction(m_actions.value(QStringLiteral("load_remote")));

    auto *helpMenu = menuBar()->addMenu(tr("&Help"));
    auto *shortcuts = helpMenu->addAction(tr("&Keyboard shortcuts"));
    connect(shortcuts, &QAction::triggered,
            this, &MainWindow::showShortcutReference);
    auto *about = helpMenu->addAction(tr("&About"));
    connect(about, &QAction::triggered, this, &MainWindow::showAbout);

    // Standard names from the icon theme, so the buttons match the rest of the
    // desktop rather than shipping bespoke art. A theme that lacks one leaves
    // that action with text alone, which still works.
    const QHash<QString, QString> themeIcons = {
        { QStringLiteral("sync"),    QStringLiteral("mail-receive") },
        { QStringLiteral("archive"), QStringLiteral("mail-mark-read") },
        { QStringLiteral("delete"),  QStringLiteral("edit-delete") },
        { QStringLiteral("undo"),    QStringLiteral("edit-undo") },
        { QStringLiteral("spam"),    QStringLiteral("mail-mark-junk") },
        { QStringLiteral("flag"),    QStringLiteral("mail-mark-important") },
        { QStringLiteral("quit"),    QStringLiteral("application-exit") },
        { QStringLiteral("focus_query"), QStringLiteral("edit-find") },
    };
    for (auto it = themeIcons.cbegin(); it != themeIcons.cend(); ++it) {
        QAction *action = m_actions.value(it.key());
        if (!action)
            continue;
        const QIcon icon = QIcon::fromTheme(it.value());
        if (!icon.isNull())
            action->setIcon(icon);
    }

    // The frequent subset only. A toolbar holding every action is as
    // unreadable as no toolbar.
    auto *toolBar = addToolBar(tr("Main"));
    toolBar->setObjectName(QStringLiteral("main_toolbar"));
    toolBar->setToolButtonStyle(Qt::ToolButtonTextBesideIcon);
    toolBar->addAction(m_actions.value(QStringLiteral("sync")));
    toolBar->addSeparator();
    toolBar->addAction(m_actions.value(QStringLiteral("archive")));
    toolBar->addAction(m_actions.value(QStringLiteral("delete")));
    toolBar->addSeparator();
    toolBar->addAction(m_actions.value(QStringLiteral("undo")));
}

void MainWindow::showShortcutReference()
{
    // Generated from the actions, so it cannot disagree with what the keys
    // really do. A hand-written list would drift the first time a binding
    // changed.
    QStringList rows;
    for (const QString &name : registeredActionNames()) {
        const QAction *action = m_actions.value(name);
        if (!action)
            continue;
        const QString sequence = action->shortcut().toString(QKeySequence::NativeText);
        rows.append(QStringLiteral("<tr><td><tt>%1</tt>&nbsp;&nbsp;</td>"
                                   "<td>%2&nbsp;&nbsp;</td>"
                                   "<td><tt>%3</tt></td></tr>")
                        .arg(sequence.isEmpty() ? tr("(unbound)") : sequence.toHtmlEscaped(),
                             m_actionDescriptions.value(name).toHtmlEscaped(),
                             name.toHtmlEscaped()));
    }

    // Two columns rather than one. Fourteen actions in a single table made a
    // dialog taller than the screen, which cut off its own title bar.
    const int half = (rows.size() + 1) / 2;
    const QString header =
        tr("<tr><th align='left'>Key</th><th align='left'>Does</th>"
           "<th align='left'>Action name</th></tr>");
    const QString left = header + rows.mid(0, half).join(QString());
    const QString right = header + rows.mid(half).join(QString());

    // A QDialog rather than QMessageBox: the message box wraps its text at a
    // narrow default width, which turned every description into a column of
    // single words and made the dialog taller than the screen.
    QDialog dialog(this);
    dialog.setWindowTitle(tr("Keyboard shortcuts"));

    auto *label = new QLabel(&dialog);
    label->setTextFormat(Qt::RichText);
    label->setText(tr("<table cellspacing='0'><tr>"
                      "<td valign='top'><table cellpadding='3'>%1</table></td>"
                      "<td width='32'></td>"
                      "<td valign='top'><table cellpadding='3'>%2</table></td>"
                      "</tr></table>")
                       .arg(left, right));

    auto *note = new QLabel(
        tr("Rebind any of these in the <tt>[keys]</tt> section of "
           "<tt>qtmaildir.conf</tt>, using the action name."),
        &dialog);
    note->setTextFormat(Qt::RichText);
    note->setWordWrap(true);

    auto *buttons = new QDialogButtonBox(QDialogButtonBox::Ok, &dialog);
    connect(buttons, &QDialogButtonBox::accepted, &dialog, &QDialog::accept);

    auto *layout = new QVBoxLayout(&dialog);
    layout->addWidget(label);
    layout->addWidget(note);
    layout->addStretch();
    layout->addWidget(buttons);

    dialog.exec();
}

void MainWindow::showAbout()
{
    QMessageBox::about(
        this, tr("About qtmaildir"),
        tr("<h3>qtmaildir %1</h3>"
           "<p>A Qt6 mail client for notmuch-indexed Maildirs.</p>"
           "<p>Reads and organizes local mail. Fetching and sending are "
           "handled by external scripts.</p>")
            .arg(QStringLiteral(QTMAILDIR_VERSION)));
}

void MainWindow::wireWorker()
{
    m_worker = new NotmuchWorker(m_config.notmuchConfig());
    m_worker->moveToThread(&m_workerThread);
    connect(&m_workerThread, &QThread::finished, m_worker, &QObject::deleteLater);

    connect(m_worker, &NotmuchWorker::threadsReady,
            this, &MainWindow::onThreadsReady);
    connect(m_worker, &NotmuchWorker::queryFinished,
            this, &MainWindow::onQueryFinished);
    connect(m_worker, &NotmuchWorker::threadLoaded,
            this, &MainWindow::onThreadLoaded);
    connect(m_worker, &NotmuchWorker::errorOccurred,
            this, &MainWindow::onWorkerError);

    // A confirmed write clears the pending revert: without this, a later
    // unrelated error would roll back a change that actually succeeded.
    connect(m_worker, &NotmuchWorker::tagsApplied, this, [this](const TagChange &) {
        m_pendingChange = {};
        m_pendingThreadIds.clear();
    });

    m_workerThread.start();
}

void MainWindow::showWarnings()
{
    const QStringList warnings = m_config.warnings() + m_keyMap.warnings();
    if (warnings.isEmpty())
        return;

    // Non-fatal: the app runs degraded rather than refusing to start.
    m_statusLabel->setText(
        tr("%n configuration warning(s)", "", warnings.size()));

    // Interrupt startup only for things that are actually wrong. Every KeyMap
    // warning qualifies (each one means a binding the user wrote is being
    // ignored), but a Config notice such as "no sync command configured" does
    // not: nothing is broken, the feature is simply off, and a modal on every
    // launch teaches the user to dismiss dialogs unread.
    const QStringList problems = m_config.problems() + m_keyMap.warnings();
    if (problems.isEmpty())
        return;

    QMessageBox::warning(this, tr("Configuration problems"),
                         problems.join(QLatin1Char('\n')));
}

void MainWindow::runCurrentQuery()
{
    QString query = m_queryEdit->text().trimmed();

    const QString accountKey = m_accountBox->currentData().toString();
    if (!accountKey.isEmpty())
        query = m_config.account(accountKey).scopedQuery(query);

    if (query.isEmpty())
        return;

    // Kept so loadThread() can work out which messages of a thread matched.
    m_lastQuery = query;

    ++m_generation;
    m_model->clear();
    m_messageView->clear();

    // Undo entries refer to rows that are about to be discarded. The model
    // update they invert would be a no-op against the new result set, leaving
    // undo half-applied: the database would change and the list would not.
    m_undoStack.clear();
    m_pendingChange = {};
    m_pendingThreadIds.clear();

    m_statusLabel->setText(tr("Searching..."));

    QMetaObject::invokeMethod(m_worker, "runQuery", Qt::QueuedConnection,
                              Q_ARG(QString, query),
                              Q_ARG(quint64, m_generation));
}

void MainWindow::onThreadsReady(const QVector<ThreadSummary> &threads,
                                quint64 generation)
{
    if (generation != m_generation)
        return;  // Superseded by a newer query.
    m_model->appendBatch(threads);
}

void MainWindow::onQueryFinished(int total, quint64 generation)
{
    if (generation != m_generation)
        return;
    m_statusLabel->setText(tr("%n thread(s)", "", total));
}

void MainWindow::onThreadSelected(const QModelIndex &current,
                                  const QModelIndex &)
{
    if (!current.isValid())
        return;

    const ThreadSummary thread = m_model->threadAt(current.row());
    m_currentThreadId = thread.threadId;
    m_messageView->setTags(thread.tags);
    QMetaObject::invokeMethod(m_worker, "loadThread", Qt::QueuedConnection,
                              Q_ARG(QString, m_currentThreadId),
                              Q_ARG(QString, m_lastQuery),
                              Q_ARG(quint64, m_generation));
}

void MainWindow::onThreadLoaded(const QVector<MessageRef> &messages,
                                quint64 generation)
{
    if (generation != m_generation || messages.isEmpty())
        return;

    MimeParser parser;
    QList<ThreadRenderItem> items;
    items.reserve(messages.size());

    for (int i = 0; i < messages.size(); ++i) {
        const MessageRef &ref = messages.at(i);

        ThreadRenderItem item;
        item.message = parser.parse(ref.filePath);

        if (!item.message.ok) {
            // One unreadable message must not lose the rest of the thread, so
            // it becomes an inline note rather than replacing the whole pane.
            item.message = {};
            item.message.ok = true;
            item.message.from = tr("(unreadable message)");
            item.message.subject = ref.filePath;
            item.message.plainBody =
                tr("This message could not be parsed.\n%1").arg(ref.filePath);
        }

        // Namespace prefix keeps cid: references distinct across the thread.
        item.cidPrefix = cidPrefixForIndex(i);

        // Matched messages open; the rest collapse to a stub. The last message
        // always opens, so a thread never renders as nothing but stubs.
        item.expanded = ref.matched || i == messages.size() - 1;

        items.append(item);
    }

    m_messageView->showThread(items);
}

void MainWindow::revertPendingTagChange()
{
    if (m_pendingThreadIds.isEmpty())
        return;

    // Put the rows back the way they were. Only the model is touched: the
    // worker never applied the change, so there is nothing to undo there.
    for (const QString &threadId : m_pendingThreadIds) {
        m_model->applyTagChange(threadId, m_pendingChange.removed,
                                m_pendingChange.added);
    }

    // The undo entry describes a change that never landed, so it would apply a
    // spurious inverse if the user pressed undo.
    if (m_undoStack.canUndo())
        m_undoStack.undo();
    m_undoStack.clear();

    m_pendingChange = {};
    m_pendingThreadIds.clear();
}

void MainWindow::onWorkerError(const QString &message)
{
    // Spec: the UI updates optimistically and reverts if the write fails.
    // Without this the list would keep showing a tag the database never got.
    revertPendingTagChange();
    m_statusLabel->setText(message);
}

void MainWindow::onSyncFinished(bool success, int exitCode)
{
    if (success) {
        m_statusLabel->setText(tr("Sync complete"));
        runCurrentQuery();
    } else {
        m_statusLabel->setText(tr("Sync failed (exit %1)").arg(exitCode));
        m_syncLog->show();
    }
}

void MainWindow::tagSelected(const QStringList &add, const QStringList &remove,
                             const QString &description)
{
    const QModelIndexList rows =
        m_threadView->selectionModel()->selectedRows();
    if (rows.isEmpty())
        return;

    QStringList threadIds;
    threadIds.reserve(rows.size());
    for (const QModelIndex &index : rows)
        threadIds.append(m_model->threadAt(index.row()).threadId);

    sendThreadTagChange(threadIds, add, remove, description);

    // Pushed for undo. The inverse re-resolves the same threads, so it works
    // whether or not those rows are still selected.
    m_undoStack.push(new ThreadTagCommand(this, threadIds, add, remove,
                                          description));

    m_statusLabel->setText(
        tr("%1: %n thread(s)", "", threadIds.size()).arg(description));
}

void MainWindow::sendThreadTagChange(const QStringList &threadIds,
                                     const QStringList &add,
                                     const QStringList &remove,
                                     const QString &description)
{
    // Optimistic: the rows change now, so a bulk archive of hundreds of threads
    // feels instant. Recorded so onWorkerError() can put them back.
    for (const QString &threadId : threadIds)
        m_model->applyTagChange(threadId, add, remove);

    // The strip shows the open thread's tags, so it has to follow a change to
    // that thread rather than waiting for the next selection.
    if (threadIds.contains(m_currentThreadId)) {
        const QModelIndex current = m_threadView->currentIndex();
        if (current.isValid())
            m_messageView->setTags(m_model->threadAt(current.row()).tags);
    }

    m_pendingThreadIds = threadIds;
    m_pendingChange = TagChange{ {}, add, remove, description };

    // The worker resolves thread ids to message ids: the UI does not hold
    // message ids for rows it never opened.
    QMetaObject::invokeMethod(m_worker, "applyTagsToThreads",
                              Qt::QueuedConnection,
                              Q_ARG(QStringList, threadIds),
                              Q_ARG(QStringList, add),
                              Q_ARG(QStringList, remove),
                              Q_ARG(QString, description));
}