refactor: Function capitalize word (#460)

* feat: implement function capitalize_word

* test: add test TestCapitalizeWordAction

fix: in CapitalizeWord add strings.Join(capWords, " ") to return.

* fix: in CapitalizeWord use Fields instead of Split to takecare of dup spaces.

* fix: redo function to keep spaces and handle unicode, add tests.

* fix: update comment for NewCapitalizeWordAction

* refactor: better readability, cleaner code in CapitalizeWord. Add test case.

internal/primitive/transform/action/strings/capitalize_word_test.go

@@ -86,4 +86,16 @@ func TestCapitalizeWordAction(t *testing.T) {
 		So(err, ShouldBeNil)
 		So(e.Extensions()["test"], ShouldEqual, "A")
 	})
+	Convey("test capitalize word: leading symbols", t, func() {
+		a, err := runtime.NewAction([]interface{}{funcName, "$.test"})
+		So(err, ShouldBeNil)
+		e := cetest.MinEvent()
+		e.SetExtension("test", "let 'em go")
+		ceCtx := &context.EventContext{
+			Event: &e,
+		}
+		err = a.Execute(ceCtx)
+		So(err, ShouldBeNil)
+		So(e.Extensions()["test"], ShouldEqual, "Let 'em Go")
+	})
 }

internal/primitive/transform/function/strings_functions.go

@@ -125,21 +125,18 @@ var CapitalizeWord = function{
 	fixedArgs: []common.Type{common.String},
 	fn: func(args []interface{}) (interface{}, error) {
 		value, _ := args[0].(string)
-		if len(value) == 0 {
-			return value, nil
-		}
-		if len(value) == 1 {
-			return strings.ToUpper(string(value[0])), nil
-		}
-		capWords := make([]rune, 0, len([]rune(value)))
-		prev := ' '
-		for _, v := range value {
-			if v != ' ' && prev == ' ' {
-				v = unicode.ToUpper(v)
+		rs := []rune(value)
+		inWord := false
+		for i, r := range rs {
+			if !unicode.IsSpace(r) {
+				if !inWord {
+					rs[i] = unicode.ToTitle(r)
+				}
+				inWord = true
+			} else {
+				inWord = false
 			}
-			capWords = append(capWords, v)
-			prev = v
 		}
-		return string(capWords), nil
+		return string(rs), nil
 	},
 }