Initial GCodeReader reading profiles from g-code

Hasn't been tested yet. Probably is wrong.

Contributes to issue CURA-34.

plugins/GCodeReader/GCodeReader.py

@@ -3,6 +3,42 @@
 
 from UM.Mesh.MeshReader import MeshReader
 
+##  A class that reads profile data from g-code files.
+#
+#   It reads the profile data from g-code files and stores the profile as a new
+#   profile, and then immediately activates that profile.
+#   This class currently does not process the rest of the g-code in any way.
 class GCodeReader(MeshReader):
+    ##  Initialises the g-code reader as a mesh reader.
+    def __init__(self):
+        super().__init__()
+
+    ##  Reads a g-code file, loading the profile from it.
     def read(self, file_name):
-        pass
+        version = 1 #IF YOU CHANGE THIS FUNCTION IN A WAY THAT BREAKS REVERSE COMPATIBILITY, INCREMENT THIS VERSION NUMBER!
+        prefix = ";SETTING_" + str(version) + " "
+        
+        #Loading all settings from the file. They are all at the end, but Python has no reverse seek any more since Python3. TODO: Consider moving settings to the start?
+        serialised = "" #Will be filled with the serialised profile.
+        try:
+            with open(file_name) as f:
+                for line in f:
+                    if line.startswith(prefix):
+                        serialised += line[len(prefix):] #Remove the prefix from the line, and add it to the rest.
+        except IOError as e:
+            Logger.log("e", "Unable to open file %s for reading: %s", file_name, str(e))
+        
+        #Unescape the serialised profile.
+        escape_characters = { #Which special characters (keys) are replaced by what escape character (values).
+                              #Note: The keys are regex strings. Values are not.
+            "\\\\": "\\", #The escape character.
+            "\\n": "\n",  #Newlines. They break off the comment.
+            "\\r": "\r"   #Carriage return. Windows users may need this for visualisation in their editors.
+        }
+        escape_characters = dict((re.escape(key), value) for key, value in escape_characters.items())
+        pattern = re.compile("|".join(escape_characters.keys()))
+        serialised = pattern.sub(lambda m: escape_characters[re.escape(m.group(0))], serialised) #Perform the replacement with a regular expression.
+        
+        #Apply the changes to the current profile.
+        profile = Application.getInstance().getMachineManager().getActiveProfile()
+        profile.unserialise(serialised)