From 6d5d31b83c0452c4a23676665291e53f09518ad7 Mon Sep 17 00:00:00 2001
From: Jan Grewe <jan.grewe@g-node.org>
Date: Sun, 27 Dec 2020 12:28:16 +0100
Subject: [PATCH] [file handler] make singleton class

---
 file_handler.py | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/file_handler.py b/file_handler.py
index bd83908..64b0c23 100644
--- a/file_handler.py
+++ b/file_handler.py
@@ -2,9 +2,17 @@ import os
 import nixio as nix
 from nixio import file
 
-class FileHandler():
+class Singleton(type):
+    _instances = {}
+    def __call__(cls, *args, **kwargs):
+        if cls not in cls._instances:
+            cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
+        return cls._instances[cls]
+
+class FileHandler(metaclass=Singleton):
     
     def __init__(self) -> None:
+        print("Handler Init")
         super().__init__()
         self._nix_file = None
         self._file_requests = []
@@ -15,7 +23,6 @@ class FileHandler():
         Args:
             filename ([type]): [description]
         """
-        print("open file: %s" % filename)
         self.close()
       
         if not os.path.exists(filename):
@@ -24,12 +31,17 @@ class FileHandler():
             self._nix_file = nix.File.open(filename, nix.FileMode.ReadOnly)
             return True, "Successfully opened file %s." % filename.split(os.sep)[-1]
         except RuntimeError as e:
-            return False, "Failed to open file %s! \n Error message is: %s" % (filename, e) 
+            return False, "Failed to open file %s! \n Error message is: %s" % (filename, e)
+        except OSError as e:
+            return False, "Failed to open file %s! \n Error message is: %s\n Probably no nix file?!" % (filename, e)
 
     def close(self):
-        print("close file")
-        # TODO check if there are any open file requests!
+        # TODO check if there are any pending file requests!
         if self._nix_file is not None and self._nix_file.is_open():
             self._nix_file.close()
             self._nix_file = None
-            self._file_requests = []
\ No newline at end of file
+            self._file_requests = []
+    
+    @property
+    def is_valid(self):
+        return self._nix_file is not None and self._nix_file.is_open()
\ No newline at end of file