Reload a project changed on disk, fingerprinted by its manifest and image sizes (12.13a)

src/IO/ProjectWatcher.cpp

@@ -0,0 +1,66 @@
+#include "IO/ProjectWatcher.h"
+#include <QFile>
+#include <QFileInfo>
+#include <sys/stat.h>
+
+ProjectWatcher::ProjectWatcher(const QString &path, std::function<void()> onChange, QObject *parent)
+    : QObject(parent), path(path), m_onChange(std::move(onChange)), m_delivery(new QTimer(this)), m_rearm(new QTimer(this))
+{
+    m_delivery->setObjectName(QStringLiteral("delivery"));
+    m_delivery->setSingleShot(true);
+    // Swift's sleeps never end early; a coarse timer may.
+    m_delivery->setTimerType(Qt::PreciseTimer);
+    m_delivery->setInterval(coalescing);
+    connect(m_delivery, &QTimer::timeout, this, [this] { m_onChange(); });
+    // A swapped-in package retires the watched inodes: arm by path.
+    m_rearm->setObjectName(QStringLiteral("rearm"));
+    m_rearm->setInterval(100);
+    m_rearm->setTimerType(Qt::PreciseTimer);
+    connect(m_rearm, &QTimer::timeout, this, [this] {
+        arm();
+        m_rearmTries += 1;
+        if (m_watcher.files().size() + m_watcher.directories().size() == watchedPaths().size() || m_rearmTries >= 20)
+            m_rearm->stop();
+    });
+    connect(&m_watcher, &QFileSystemWatcher::fileChanged, this, &ProjectWatcher::noteEvent);
+    connect(&m_watcher, &QFileSystemWatcher::directoryChanged, this, &ProjectWatcher::noteEvent);
+    // The parent's other entries are not ours: only another package.
+    connect(&m_parent, &QFileSystemWatcher::directoryChanged, this, [this] {
+        if (identity() != m_identity)
+            noteEvent();
+    });
+    m_parent.addPath(QFileInfo(path).absolutePath());
+    arm();
+}
+
+QStringList ProjectWatcher::watchedPaths() const
+{
+    return {path, path + QStringLiteral("/manifest.json"), path + QStringLiteral("/images")};
+}
+
+std::optional<std::pair<dev_t, ino_t>> ProjectWatcher::identity() const
+{
+    struct stat status;
+    if (::stat(QFile::encodeName(path).constData(), &status) != 0)
+        return std::nullopt;
+    return std::pair(status.st_dev, status.st_ino);
+}
+
+void ProjectWatcher::arm()
+{
+    m_identity = identity();
+    const QStringList watched = m_watcher.files() + m_watcher.directories();
+    if (!watched.isEmpty())
+        m_watcher.removePaths(watched);
+    for (const QString &each : watchedPaths()) {
+        if (QFileInfo::exists(each))
+            m_watcher.addPath(each);
+    }
+}
+
+void ProjectWatcher::noteEvent()
+{
+    m_rearmTries = 0;
+    m_rearm->start();
+    m_delivery->start();
+}