add datacheck for empty tags

fixes #12

acros/templates/acros/datacheck.html

@@ -11,9 +11,15 @@
       <strong>{{ error.obj }}</strong>:
       {{ error.msg }}
       <br>
+      {% if error.obj.get_absolute_url %}
         <a href="{{ error.obj.get_absolute_url }}" class="alert-link">View</a>
+      {% endif %}
+      {% if error.edit_url %}
         <a href="{{ error.edit_url }}" class="alert-link">Edit</a>
+      {% endif %}
+      {% if error.admin_edit_url %}
         <a href="{{ error.admin_edit_url }}" class="alert-link">Admin-Edit</a>
+      {% endif %}
     </div>
   {% empty %}
     <div class="alert alert-success" role="alert">

acros/utils/checks/__init__.py

@@ -3,3 +3,4 @@ from .check_registry import CheckRegistry, registry
 from .messages import DEBUG, INFO, WARNING, ERROR, CRITICAL, CheckMessage, CheckWarning, CheckInfo
 from .checks.acronym import *
 from .checks.image import *
+from .checks.tags import *

acros/utils/checks/checks/tags.py

@@ -0,0 +1,13 @@
+from acros.models import Tag
+from acros.utils.checks import BaseCheck, CheckWarning, registry
+
+
+class TagsCheck(BaseCheck):
+    def run(self):
+        for tag in Tag.objects.filter(acronyms=None):
+            yield CheckWarning(
+                "Tag is unused",
+                obj=tag)
+
+
+registry.register(TagsCheck)

acros/utils/checks/messages.py

@@ -1,6 +1,6 @@
 from django.urls import reverse
 
-from acros.models import Acronym
+from acros.models import Acronym, Tag
 
 DEBUG = 10
 INFO = "info"
@@ -30,6 +30,8 @@ class CheckMessage:
     def admin_edit_url(self):
         if isinstance(self.obj, Acronym):
             return reverse("admin:acros_acronym_change", args=[self.obj.id])
+        if isinstance(self.obj, Tag):
+            return reverse("admin:acros_tag_change", args=[self.obj.id])
         return None