From 3554b549410128c149c2927e81abd5c4516e8c6a Mon Sep 17 00:00:00 2001
From: Martin Molnar <martin.molnar@nangu.tv>
Date: Fri, 15 Jun 2018 12:42:20 +0200
Subject: [PATCH] add template function to multiply values

---
 template/functions.go |  1 +
 template/multiply.go  | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 template/multiply.go

diff --git a/template/functions.go b/template/functions.go
index 8fa77fb8..2b835fd9 100644
--- a/template/functions.go
+++ b/template/functions.go
@@ -23,6 +23,7 @@ var funcs functions = make(map[string]functionWithValidator)
 
 func init() {
 	funcs.add("timestamp", newTimestampFunc())
+	funcs.add("multiply", newMultiplyFunc())
 }
 
 type functions map[string]functionWithValidator
diff --git a/template/multiply.go b/template/multiply.go
new file mode 100644
index 00000000..86b82918
--- /dev/null
+++ b/template/multiply.go
@@ -0,0 +1,36 @@
+package template
+
+import (
+	"fmt"
+	"strconv"
+	"text/template/parse"
+)
+
+func newMultiplyFunc() functionWithValidator {
+	return functionWithValidator{
+		function:        multiply,
+		staticValidator: validateMultiplyCall,
+	}
+}
+
+func multiply(value string, multiplier float64) (float64, error) {
+	i, err := strconv.ParseFloat(value, 64)
+	if err != nil {
+		return 0, err
+	}
+
+	return i * multiplier, nil
+}
+
+func validateMultiplyCall(cmd *parse.CommandNode) error {
+	prefix := "syntax error in shift call"
+	if len(cmd.Args) != 3 {
+		return fmt.Errorf("%v: expected two parameters, but found %v parameters", prefix, len(cmd.Args)-1)
+	}
+	exponentNode, ok := cmd.Args[2].(*parse.NumberNode)
+	if !ok || !exponentNode.IsFloat {
+		return fmt.Errorf("%v: unable to parse %v as a float number", prefix, exponentNode.Text)
+	}
+
+	return nil
+}