descpage: Prepare gnuplot script for wiki

We need to replace environment variable usage to simplify script usage
and be platform independent

Issue #1 (https://git.golderweb.de/wiki/jogobot-euroexchange/issues/1)

euroexchange/descpage.py

@@ -64,6 +64,26 @@ class DescPageBot(pywikibot.bot.Bot):
             Config.gnuplot_script_dir, self.job.script + ".plt" ), "r") as fd:
                 return fd.read()
 
+    def prepare_gnuplot_script(self):
+        """
+        Prepare gnuplot script code for publishing on image description page
+        """
+
+        # Load gnuplot script
+        gnuplot_script = self.load_gnuplot_script()
+
+        # Strip leadig and trailing whitespace
+        gnuplot_script = gnuplot_script.strip(" \n")
+
+        # Replace
+        gnuplot_script = gnuplot_script.\
+            replace( "system(\"echo $INFILE\")",
+                      "'{}'".format( os.path.basename( Config.csv_file ) ) ).\
+            replace( "system(\"echo $OUTFILE\")",
+                      "'{}'".format (os.path.basename( self.job.image ) ) )
+
+        return gnuplot_script
+
     def parse_page(self):
         """
         Load current page content and parse with mwparser