diff -r eb479baeb2bf -r fb86765b4c54 src/hdalab/utils.py
--- a/src/hdalab/utils.py	Tue Jul 08 12:03:06 2014 +0200
+++ b/src/hdalab/utils.py	Wed Jul 09 12:26:11 2014 +0200
@@ -2,17 +2,56 @@
 '''
 Created on Mar 13, 2012
 
-@author: ymh
+@author: ymh and tc
 '''
 from django.core.cache import cache
+from django.http.response import Http404
 from django.utils.encoding import smart_str
 import md5
 import re
 
+import logging
+logger = logging.getLogger(__name__)
+
 
 def fix_cache_key(key):
     cache_key = re.sub(r'\s+', '-', key)
     cache_key = smart_str(cache_key)
     if len(cache_key) > (250-(2+len(cache.key_prefix)+len(str(cache.version)))-33):
         cache_key = cache_key[:(250-(2+len(cache.key_prefix)+len(str(cache.version)))-33)] + '-' + md5.new(cache_key).hexdigest()
-    return cache_key
\ No newline at end of file
+    return cache_key
+
+
+
+class NodePlacer():
+    
+    cat_nb_nodes = {}
+    
+    def init(self, cat_nb_nodes_initial):
+        raise NotImplementedError( "Should have implemented get_place" )
+    
+    def get_place(self, category):
+        if not category or category not in self.cat_nb_nodes:
+            raise Http404
+        return self.cat_nb_nodes[category].pop(0)
+
+
+
+class LineNodePlacer(NodePlacer):
+    
+    max_length = 0
+    
+    def init(self, cat_nb_nodes_initial):
+        for c in cat_nb_nodes_initial:
+            self.max_length = cat_nb_nodes_initial[c] if cat_nb_nodes_initial[c] > self.max_length else self.max_length
+        for i_cat,c in enumerate(cat_nb_nodes_initial):
+            self.cat_nb_nodes[c] = []
+            offset = float(self.max_length - cat_nb_nodes_initial[c]) / 2
+            for i in xrange(cat_nb_nodes_initial[c]):
+                self.cat_nb_nodes[c].append({ "x": i_cat*200, "y": 100*(i+offset) })
+        #logger.debug(self.cat_nb_nodes)
+        
+                
+    
+        
+        
\ No newline at end of file