Introduce startmermaid block tag

Author: maiksprenger

src/django_mermaid/templatetags/mermaid.py

@@ -1,3 +1,4 @@
+import ast
 import json
 
 from django import template
@@ -14,7 +15,9 @@
 @register.simple_tag
 @mark_safe
 def mermaid(diagram=None, theme=None):
-    """Render a mermaid diagram.
+    """Render a mermaid diagram, using a simple tag.
+
+    {% mermaid "graph LR; A-->B;" "dark" %}
 
     :param diagram: The mermaid diagram definition
     :param theme: The mermaid theme to use (default, forest, dark, neutral, base). See https://mermaid.js.org/config/theming.
@@ -28,3 +31,43 @@ def mermaid(diagram=None, theme=None):
     html = "<div class=\"mermaid\">%s</div><script src=\"%s\"></script>" % (diagram or "", mermaid_uri)
     init_properties = {"startOnLoad": True, "theme": theme, "themeVariables": theme_variables}
     return html + "<script>mermaid.initialize(%s);</script>" % json.dumps(init_properties)
+
+
+@register.tag(name="startmermaid")
+def do_startmermaid(parser, token):
+    """Render a mermaid diagram, using a block tag.
+
+    {% startmermaid "dark" %}
+        graph LR
+            A-->B
+    {% endmermaid %}
+
+    This tag is identical to the {% mermaid %} simple tag but allows usage as a block.
+    That can be useful for longer diagrams. Specifying the theme is optional.
+    """
+    # Split the token to try to capture a theme parameter if provided
+    bits = token.split_contents()
+    if len(bits) > 1:
+        # Strip surrounding quotes
+        theme = ast.literal_eval(bits[1])
+    else:
+        theme = None
+
+    # Parse everything until the end tag 'endmermaid'
+    nodelist = parser.parse(('endmermaid',))
+    parser.delete_first_token()
+
+    return MermaidNode(nodelist, theme)
+
+
+class MermaidNode(template.Node):
+    def __init__(self, nodelist, theme):
+        self.nodelist = nodelist
+        self.theme = theme
+
+    def render(self, context):
+        # Render the diagram from the block
+        diagram_content = self.nodelist.render(context)
+        # Pass processing on to the simple template tag
+        return mermaid(diagram=diagram_content, theme=self.theme)
+