Add QgsFileUtils::findClosestExistingPath to find the closest

existing folder match for a path

E.g. if \a path is "/home/user/projects/2018/P4343"
and "/home/user/projects" exists but no "2018" subfolder
exists, then the function will return "/home/user/projects".

(Suprisingly no existing Qt method for this!)

python/core/auto_generated/qgsfileutils.sip.in

@@ -75,6 +75,14 @@ for filenames with an '_' character.
 .. warning::
 
    This method strips slashes from the filename, so it is safe to call with file names only, not complete paths.
+%End
+
+    static QString findClosestExistingPath( const QString &path );
+%Docstring
+Returns the top-most existing folder from ``path``. E.g. if ``path`` is "/home/user/projects/2018/P4343"
+and "/home/user/projects" exists but no "2018" subfolder exists, then the function will return "/home/user/projects".
+
+.. versionadded:: 3.2
 %End
 };
 

src/core/qgsfileutils.cpp

@@ -15,6 +15,8 @@
 #include "qgsfileutils.h"
 #include <QObject>
 #include <QRegularExpression>
+#include <QFileInfo>
+#include <QDir>
 
 QString QgsFileUtils::representFileSize( qint64 bytes )
 {
@@ -29,7 +31,7 @@ QString QgsFileUtils::representFileSize( qint64 bytes )
     unit = i.next();
     bytes /= 1024.0;
   }
-  return QString( "%1 %2" ).arg( QString::number( bytes ), unit );
+  return QStringLiteral( "%1 %2" ).arg( QString::number( bytes ), unit );
 }
 
 QStringList QgsFileUtils::extensionsFromFilter( const QString &filter )
@@ -86,8 +88,29 @@ QString QgsFileUtils::addExtensionFromFilter( const QString &fileName, const QSt
 
 QString QgsFileUtils::stringToSafeFilename( const QString &string )
 {
-  QRegularExpression rx( "[/\\\\\\?%\\*\\:\\|\"<>]" );
+  QRegularExpression rx( QStringLiteral( "[/\\\\\\?%\\*\\:\\|\"<>]" ) );
   QString s = string;
   s.replace( rx, QStringLiteral( "_" ) );
   return s;
 }
+
+QString QgsFileUtils::findClosestExistingPath( const QString &path )
+{
+  QDir currentPath;
+  QFileInfo fi( path );
+  if ( fi.isFile() )
+    currentPath = fi.dir();
+  else
+    currentPath = QDir( path );
+
+  while ( !currentPath.exists() )
+  {
+    const QString parentPath = QDir::cleanPath( currentPath.path() + QStringLiteral( "/.." ) );
+    if ( parentPath.isEmpty() || parentPath == '.' )
+      return QString();
+    currentPath = QDir( parentPath );
+  }
+
+  const QString res = QDir::cleanPath( currentPath.path() );
+  return res == '.' ? QString() : res;
+}

src/core/qgsfileutils.h

@@ -78,6 +78,14 @@ class CORE_EXPORT QgsFileUtils
      * \warning This method strips slashes from the filename, so it is safe to call with file names only, not complete paths.
      */
     static QString stringToSafeFilename( const QString &string );
+
+    /**
+     * Returns the top-most existing folder from \a path. E.g. if \a path is "/home/user/projects/2018/P4343"
+     * and "/home/user/projects" exists but no "2018" subfolder exists, then the function will return "/home/user/projects".
+     *
+     * \since QGIS 3.2
+     */
+    static QString findClosestExistingPath( const QString &path );
 };
 
 #endif // QGSFILEUTILS_H

tests/src/python/test_qgsfileutils.py

@@ -14,6 +14,8 @@
 
 import qgis  # NOQA
 
+import tempfile
+import os
 from qgis.core import QgsFileUtils
 from qgis.testing import unittest
 
@@ -61,6 +63,35 @@ def testStringToSafeFilename(self):
             QgsFileUtils.stringToSafeFilename('rendered map_final? rev (12-03-1017)_real/\\?%*:|"<>.tif'),
             'rendered map_final_ rev (12-03-1017)_real__________.tif')
 
+    def testFindClosestExistingPath(self):
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(''), '')
+        self.assertEqual(QgsFileUtils.findClosestExistingPath('.'), '')
+        self.assertEqual(QgsFileUtils.findClosestExistingPath('a_very_unlikely_path_to_really_exist/because/no_one_would_have_a_folder_called/MapInfo is the bestest/'), '')
+        # sorry anyone not on linux!
+        self.assertEqual(QgsFileUtils.findClosestExistingPath('/usr/youve_been_hacked/by_the_l77t_krew'), '/usr')
+
+        base_path = tempfile.mkdtemp()
+        file = os.path.join(base_path, 'test.csv')
+        with open(file, 'wt') as f:
+            f.write('\n')
+
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(os.path.join(base_path, 'a file name.bmp')), base_path) # non-existant file
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(file), base_path) # real file!
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(os.path.join(base_path, 'non/existant/subfolder')), base_path)
+
+        sub_folder1 = os.path.join(base_path, 'subfolder1')
+        os.mkdir(sub_folder1)
+        sub_folder2 = os.path.join(sub_folder1, 'subfolder2')
+        os.mkdir(sub_folder2)
+        bad_sub_folder = os.path.join(sub_folder2, 'nooo')
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(bad_sub_folder), sub_folder2)
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(sub_folder2), sub_folder2)
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(sub_folder2 + '/.'), sub_folder2)
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(sub_folder2 + '/..'), sub_folder1)
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(sub_folder2 + '/../ddddddd'), sub_folder1)
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(sub_folder2 + '/../subfolder2'), sub_folder2)
+        self.assertEqual(QgsFileUtils.findClosestExistingPath(sub_folder2 + '/../subfolder2/zxcv/asfdasd'), sub_folder2)
+
 
 if __name__ == '__main__':
     unittest.main()