feat(changelog): add string functions for changelog template

internal/changelog/changelog.go

@@ -1,6 +1,7 @@
 package changelog
 
 import (
+	"bufio"
 	"bytes"
 	"io/ioutil"
 	"strings"
@@ -180,6 +181,10 @@ func generateTemplate(text string, values interface{}) (string, error) {
 
 	funcMap := template.FuncMap{
 		"replace": replace,
+		"lower": lower,
+		"upper": upper,
+		"capitalize": capitalize,
+		"addPrefixToLines": addPrefixToLines,
 	}
 
 	var tpl bytes.Buffer
@@ -197,3 +202,30 @@ func generateTemplate(text string, values interface{}) (string, error) {
 func replace(input, from, to string) string {
 	return strings.Replace(input, from, to, -1)
 }
+
+func lower(input string) string {
+	return strings.ToLower(input)
+}
+
+func upper(input string) string {
+	return strings.ToUpper(input)
+}
+
+func capitalize(input string) string {
+	if len(input) > 0 {
+		return strings.ToUpper(string(input[0])) + input[1:]
+	}
+	return ""
+}
+
+// Adds a prefix to each line of the given text block
+// this can be helpful in rendering correct indentation or bullets for multi-line texts
+func addPrefixToLines(input, prefix string) string {
+	output := ""
+	scanner := bufio.NewScanner(strings.NewReader(input))
+	for scanner.Scan() {
+		output += prefix + scanner.Text() + "\n"
+	}
+	output = strings.TrimRight(output, "\n")
+	return output
+}