Merge pull request #862 from MITx/feature/victor/capa-ajax

Feature/victor/capa ajax

I'm happy with all the changes to inputtypes, modulo the minor comments.
I didn't read chemcalc.py closely, but the tests look good.

lms/djangoapps/courseware/module_render.py

@@ -1,6 +1,7 @@
 import hashlib
 import json
 import logging
+import pyparsing
 import sys
 
 from django.conf import settings
@@ -13,6 +14,7 @@ from django.views.decorators.csrf import csrf_exempt
 from requests.auth import HTTPBasicAuth
 
 from capa.xqueue_interface import XQueueInterface
+from capa.chem import chemcalc
 from courseware.access import has_access
 from mitxmako.shortcuts import render_to_string
 from models import StudentModule, StudentModuleCache
@@ -471,3 +473,42 @@ def modx_dispatch(request, dispatch, location, course_id):
 
     # Return whatever the module wanted to return to the client/caller
     return HttpResponse(ajax_return)
+
+def preview_chemcalc(request):
+    """
+    Render an html preview of a chemical formula or equation.  The fact that
+    this is here is a bit of hack.  See the note in lms/urls.py about why it's
+    here. (Victor is to blame.)
+
+    request should be a GET, with a key 'formula' and value 'some formula string'.
+
+    Returns a json dictionary:
+    {
+       'preview' : 'the-preview-html' or ''
+       'error' : 'the-error' or ''
+    }
+    """
+    if request.method != "GET":
+        raise Http404
+
+    result = {'preview': '',
+              'error': '' }
+    formula = request.GET.get('formula')
+    if formula is None:
+        result['error'] = "No formula specified."
+
+        return HttpResponse(json.dumps(result))
+
+    try:
+        result['preview'] = chemcalc.render_to_html(formula)
+    except pyparsing.ParseException as p:
+        result['error'] = "Couldn't parse formula: {0}".format(p)
+    except Exception:
+        # this is unexpected, so log
+        log.warning("Error while previewing chemical formula", exc_info=True)
+        result['error'] = "Error while rendering preview"
+
+    return HttpResponse(json.dumps(result))
+
+
+