Start: fixes #17857: Icon-files of the startup screen are not removed from /tmp

It's basically a port of #10951 to the new start page implementation.

Note: Icon files are not removed but re-used instead.

The commit adds some new functions:

* getThumbnailsImage()
  Returns the name of the PNG inside a project file

* getThumbnailsName()
  Returns the directory name containing the image files

* getThumnailsParentDir()
  Returns the parent directory of the directory containing the image files

* getThumbnailsDir()
  Returns the path to the thumbnail directory. There is no need to always create a unique directory
  after each restart because it doesn't harm if the thumbnail directoy contains deprecated files.

* createThumbnailsDir()
  Creates the thumbnail directoy if it doesn't exist yet.

* getSha1Hash
  Helper function to compute a SHA-1 hash of a given path. If the same path is passed
  then the hash value will be the same.
  This way it can be avoided to create a different image file from a project file
  after each restart.

* getUniquePNG
  Computes the path of a PNG image file for a given project file. It's also possible
  to pass an arbitrary string as argument.

* useCachedPNG
  If the PNG image exists and if it's newer than the project file True is returned
  and False otherwise.

For a given project file it is checked if the thumbnail directory already contains
a cached image. If it's newer than the project file it will used, otherwise it will
be re-created.

Fix freecadCanOpen() abd DisplayedFilesModel::addFile() to also check for lower-case
file extensions.

src/Mod/Start/App/DisplayedFilesModel.cpp

@@ -23,7 +23,11 @@
 
 #include "PreCompiled.h"
 #ifndef _PreComp_
+#include <boost/algorithm/string/predicate.hpp>
 #include <QByteArray>
+#include <QCryptographicHash>
+#include <QDateTime>
+#include <QDir>
 #include <QFile>
 #include <QFileInfo>
 #endif
@@ -31,6 +35,8 @@
 #include "DisplayedFilesModel.h"
 #include <App/Application.h>
 #include <App/ProjectFile.h>
+#include <Base/FileInfo.h>
+#include <Base/Stream.h>
 
 using namespace Start;
 
@@ -80,6 +86,68 @@ FileStats fileInfoFromFreeCADFile(const std::string& path)
     return result;
 }
 
+std::string getThumbnailsImage()
+{
+    return "thumbnails/Thumbnail.png";
+}
+
+QString getThumbnailsName()
+{
+    return QString::fromLatin1("FreeCADStartThumbnails");
+}
+
+QDir getThumnailsParentDir()
+{
+    return QDir::temp();
+}
+
+QString getThumbnailsDir()
+{
+    QDir dir = getThumnailsParentDir();
+    return dir.absoluteFilePath(getThumbnailsName());
+}
+
+void createThumbnailsDir()
+{
+    QString name = getThumbnailsName();
+    QDir dir(getThumnailsParentDir());
+    if (!dir.exists(name)) {
+        dir.mkpath(name);
+    }
+}
+
+QString getSha1Hash(const std::string& path)
+{
+    QCryptographicHash hash(QCryptographicHash::Sha1);
+    hash.addData(path.c_str(), static_cast<int>(path.size()));
+    QByteArray ba1 = hash.result().toHex();
+    hash.reset();
+    hash.addData(ba1);
+    QByteArray ba2 = hash.result().toHex();
+    return QString::fromLatin1(ba2);
+}
+
+QString getUniquePNG(const std::string& path)
+{
+    QDir dir = getThumbnailsDir();
+    QString sha1 = getSha1Hash(path) + QLatin1String(".png");
+    return dir.absoluteFilePath(sha1);
+}
+
+bool useCachedPNG(const std::string& image, const std::string& project)
+{
+    Base::FileInfo f1(image);
+    Base::FileInfo f2(project);
+    if (!f1.exists()) {
+        return false;
+    }
+    if (!f2.exists()) {
+        return false;
+    }
+
+    return f1.lastModified() > f2.lastModified();
+}
+
 /// Load the thumbnail image data (if any) that is stored in an FCStd file.
 /// \returns The image bytes, or an empty QByteArray (if no thumbnail was stored)
 QByteArray loadFCStdThumbnail(const std::string& pathToFCStdFile)
@@ -87,9 +155,20 @@ QByteArray loadFCStdThumbnail(const std::string& pathToFCStdFile)
     App::ProjectFile proj(pathToFCStdFile);
     if (proj.loadDocument()) {
         try {
-            std::string thumbnailFile = proj.extractInputFile("thumbnails/Thumbnail.png");
-            if (!thumbnailFile.empty()) {
-                auto inputFile = QFile(QString::fromStdString(thumbnailFile));
+            std::string thumbnailFile = getUniquePNG(pathToFCStdFile).toStdString();
+            if (!useCachedPNG(thumbnailFile, pathToFCStdFile)) {
+                static std::string thumb = getThumbnailsImage();
+                if (proj.containsFile(thumb)) {
+                    createThumbnailsDir();
+                    Base::FileInfo fi(thumbnailFile);
+                    Base::ofstream str(fi);
+                    proj.readInputFileDirect(thumb, str);
+                    str.close();
+                }
+            }
+
+            auto inputFile = QFile(QString::fromStdString(thumbnailFile));
+            if (inputFile.exists()) {
                 inputFile.open(QIODevice::OpenModeFlag::ReadOnly);
                 return inputFile.readAll();
             }
@@ -115,6 +194,19 @@ FileStats getFileInfo(const std::string& path)
     result.insert(std::make_pair(DisplayedFilesModelRoles::baseName, file.fileName()));
     return result;
 }
+
+bool freecadCanOpen(const QString& extension)
+{
+    std::string ext = extension.toStdString();
+    auto importTypes = App::GetApplication().getImportTypes();
+    return std::find_if(importTypes.begin(),
+                        importTypes.end(),
+                        [&ext](const auto& item) {
+                            return boost::iequals(item, ext);
+                        })
+        != importTypes.end();
+}
+
 }  // namespace
 
 DisplayedFilesModel::DisplayedFilesModel(QObject* parent)
@@ -177,13 +269,6 @@ QVariant DisplayedFilesModel::data(const QModelIndex& index, int roleAsInt) cons
     return {};
 }
 
-bool freecadCanOpen(const QString& extension)
-{
-    auto importTypes = App::GetApplication().getImportTypes();
-    return std::find(importTypes.begin(), importTypes.end(), extension.toStdString())
-        != importTypes.end();
-}
-
 void DisplayedFilesModel::addFile(const QString& filePath)
 {
     QFileInfo qfi(filePath);
@@ -194,7 +279,7 @@ void DisplayedFilesModel::addFile(const QString& filePath)
         return;
     }
     _fileInfoCache.emplace_back(getFileInfo(filePath.toStdString()));
-    if (qfi.completeSuffix() == QLatin1String("FCStd")) {
+    if (qfi.completeSuffix().toLower() == QLatin1String("fcstd")) {
         auto thumbnail = loadFCStdThumbnail(filePath.toStdString());
         if (!thumbnail.isEmpty()) {
             _imageCache.insert(filePath, thumbnail);

src/Mod/Start/App/PreCompiled.h

@@ -42,7 +42,13 @@
 #include <vector>
 #include <unordered_map>
 
+// boost
+#include <boost/algorithm/string/predicate.hpp>
+
 // Qt (should never include GUI files, only QtCore)
+#include <QByteArray>
+#include <QCryptographicHash>
+#include <QDateTime>
 #include <QDir>
 #include <QFile>
 #include <QFileInfo>