[counter] Add counterValueAdd template function

Signed-off-by: Knut Ahlers <knut@ahlers.me>

internal/actors/counter/actor.go

@@ -137,6 +137,19 @@ func Register(args plugins.RegistrationArguments) error {
 		return GetCounterValue(db, name)
 	}))
 
+	args.RegisterTemplateFunction("counterValueAdd", plugins.GenericTemplateFunctionGetter(func(name string, val ...int64) (int64, error) {
+		var mod int64 = 1
+		if len(val) > 0 {
+			mod = val[0]
+		}
+
+		if err := UpdateCounter(db, name, mod, false); err != nil {
+			return 0, errors.Wrap(err, "updating counter")
+		}
+
+		return GetCounterValue(db, name)
+	}))
+
 	return nil
 }
 

wiki/Templating.md

@@ -82,6 +82,18 @@ Example:
 < 5
 ```
 
+#### `counterValueAdd`
+
+Adds the given value (or 1 if no value) to the counter and returns its new value
+
+Syntax: `counterValueAdd <counter name> [increase=1]`
+
+Example:
+```
+# {{ counterValueAdd "myCounter" }} {{ counterValueAdd "myCounter" 5 }}
+< 1 6
+```
+
 #### `displayName`
 
 Returns the display name the specified user set for themselves