core: introduce new markdown input

To fix
* Avoid blinking in preview
* Don't insert stupid space on empty textarea

core/templates/core/markdown_textarea.jinja

@@ -0,0 +1,62 @@
+<div>
+	<textarea name="{{ widget.name }}"{% include "django/forms/widgets/attrs.html" %}>
+	{% if widget.value %}{{ widget.value }}{% endif %}</textarea>
+
+	{# The simplemde script can be included twice, it's safe in the code #}
+	<script src="{{ statics.js }}"> </script>
+	<script type="text/javascript">
+		var css = "{{ statics.css }}";
+
+		// Only import the css once
+		if (!document.head.innerHTML.includes(css)){
+			document.head.innerHTML += '<link rel="stylesheet" href="' + css + '">';
+		}
+
+		// You can't get the csrf token from the template in a widget
+		// We get it from a cookie as a workaround, see this link
+		// https://docs.djangoproject.com/en/2.0/ref/csrf/#ajax
+		function getCookie(name) {
+			var cookieValue = null;
+			if (document.cookie && document.cookie !== '') {
+				var cookies = document.cookie.split(';');
+				for (var i = 0; i < cookies.length; i++) {
+					var cookie = jQuery.trim(cookies[i]);
+					// Does this cookie string begin with the name we want?
+					if (cookie.substring(0, name.length + 1) === (name + '=')) {
+						cookieValue = decodeURIComponent(cookie.substring(name.length + 1));
+						break;
+					}
+				}
+			}
+			return cookieValue;
+		}
+
+
+		// Custom markdown parser
+		function customMarkdownParser(plainText, preview) {
+			// Wait for jquery to load
+			var waitForJquery = setInterval(function () {
+				if (typeof $ != 'undefined'){
+					clearInterval(waitForJquery)
+					$.ajax({
+						url: "{{ markdown_api_url }}",
+						method: "POST",
+						data: { text: plainText, csrfmiddlewaretoken: getCookie('csrftoken') },
+					}).done(function (msg) {
+						preview.innerHTML = msg;
+					});
+				}
+			}, 10);
+		}
+
+		// Pretty markdown input
+		var simplemde = new SimpleMDE({
+			element: document.getElementById("{{ widget.attrs.id }}"),
+			spellChecker: false,
+			previewRender: function(plainText, preview){ // Async method
+				customMarkdownParser(plainText, preview);
+			}
+		});
+
+	</script>
+</div>

core/views/forms.py

@@ -26,6 +26,8 @@ from django.contrib.auth.forms import UserCreationForm, AuthenticationForm
 from django import forms
 from django.conf import settings
 from django.db import transaction
+from django.templatetags.static import static
+from django.core.urlresolvers import reverse
 from django.core.exceptions import ValidationError
 from django.forms import (
     CheckboxSelectMultiple,
@@ -90,19 +92,17 @@ class SelectDate(DateInput):
 
 
 class MarkdownInput(Textarea):
-    def render(self, name, value, attrs=None):
-        output = (
-            '<p><a href="%(syntax_url)s">%(help_text)s</a></p>'
-            '<div class="markdown_editor">%(content)s</div>'
-            % {
-                "syntax_url": Page.get_page_by_full_name(
-                    settings.SITH_CORE_PAGE_SYNTAX
-                ).get_absolute_url(),
-                "help_text": _("Help on the syntax"),
-                "content": super(MarkdownInput, self).render(name, value, attrs),
-            }
-        )
-        return output
+    template_name = "core/markdown_textarea.jinja"
+
+    def get_context(self, name, value, attrs):
+        context = super(MarkdownInput, self).get_context(name, value, attrs)
+
+        context["statics"] = {
+            "js": static("core/simplemde/simplemde.min.js"),
+            "css": static("core/simplemde/simplemde.min.css"),
+        }
+        context["markdown_api_url"] = reverse("api:api_markdown")
+        return context
 
 
 class SelectFile(TextInput):