[common][permissions] Implement permissions from various mixins

This will allow to remove mixins that where going special
permission management.

Removing these mixins will allow for more flexibility with
regard to permission management.

beat/web/common/permissions.py

@@ -50,3 +50,41 @@ class IsAuthor(permissions.IsAuthenticated):
             author_name = kwargs.get("author_name")
             allowed = request.user.username == author_name
         return allowed
+
+
+class IsAuthorOrReadOnly(IsAuthor):
+    """
+    Either allow access if using a read method or
+    check that the user is also the author.
+    """
+
+    def has_permission(self, request, view):
+        if request.method in permissions.SAFE_METHODS:
+            return True
+        else:
+            return super().has_permission(request, view)
+
+
+class IsAdminOrReadOnly(permissions.IsAdminUser):
+    """
+    Either allow access if using a read method or
+    check that the user is an admin.
+    """
+
+    def has_permission(self, request, view):
+        if request.method in permissions.SAFE_METHODS:
+            return True
+        else:
+            return super().has_permission(request, view)
+
+
+class IsModifiableOrRead(permissions.BasePermission):
+    """
+    Check for modifiable flag if there's a modification that is tried
+    """
+
+    def has_object_permission(self, request, view, obj):
+        if request.method in permissions.SAFE_METHODS:
+            return True
+        else:
+            return obj.modifiable()