runtime: add method to lookup a file by name without selecting it

In some cases it might come in handy to be able to lookup a random file
in the file system tree before actually selecting it. This would be
very useful in situations where we need to check the presence of the
file or if we need to check certain file attributes before performing
some task.

Related: OS#6092
Change-Id: I6b6121e749cea843163659e1a26bb3893c032e29

pySim/runtime.py

@@ -234,6 +234,42 @@ class RuntimeLchan:
             node = node.parent
         return None
 
+    def get_file_by_name(self, name: str) -> CardFile:
+        """Obtain the file object from the file system tree by its name without actually selecting the file.
+
+        Returns:
+            CardFile() instance or None"""
+
+        # handling of entire paths with multiple directories/elements
+        if '/' in name:
+            pathlist = name.split('/')
+            # treat /DF.GSM/foo like MF/DF.GSM/foo
+            if pathlist[0] == '':
+                pathlist[0] = 'MF'
+        else:
+            pathlist = [name]
+
+        # start in the current working directory (we can still
+        # select any ADF and the MF from here, so those will be
+        # among the selectables).
+        file = self.get_cwd()
+
+        for p in pathlist:
+            # Look for the next file in the path list
+            selectables = file.get_selectables().items()
+            file = None
+            for selectable in selectables:
+                if selectable[1].name == name:
+                    file = selectable[1]
+                    break
+
+            # When we hit none, then the given path must be invalid
+            if file is None:
+                return None
+
+        # Return the file object found at the tip of the path
+        return file
+
     def interpret_sw(self, sw: str):
         """Interpret a given status word relative to the currently selected application
         or the underlying card profile.