Function to convert to upper snake case

Closes #6

snake.go

@@ -9,7 +9,12 @@ import (
 
 // SnakeCase converts a string into snake case.
 func SnakeCase(s string) string {
-	return lowerDelimiterCase(s, '_')
+	return delimiterCase(s, '_', false)
+}
+
+// UpperSnakeCase converts a string into snake case with capital letters.
+func UpperSnakeCase(s string) string {
+	return delimiterCase(s, '_', true)
 }
 
 // lowerDelimiterCase converts a string into snake_case or kebab-case depending on
@@ -46,3 +51,43 @@ func lowerDelimiterCase(s string, delimiter rune) string {
 
 	return string(buffer)
 }
+
+// delimiterCase converts a string into snake_case or kebab-case depending on the delimiter passed
+// as second argument. When upperCase is true the result will be UPPER_SNAKE_CASE or UPPER-KEBAB-CASE.
+func delimiterCase(s string, delimiter rune, upperCase bool) string {
+	s = strings.TrimSpace(s)
+	buffer := make([]rune, 0, len(s)+3)
+
+	adjustCase := toLower
+	if upperCase {
+		adjustCase = toUpper
+	}
+
+	var prev rune
+	var curr rune
+	for _, next := range s {
+		if isDelimiter(curr) {
+			if !isDelimiter(prev) {
+				buffer = append(buffer, delimiter)
+			}
+		} else if isUpper(curr) {
+			if isLower(prev) || (isUpper(prev) && isLower(next)) {
+				buffer = append(buffer, delimiter)
+			}
+			buffer = append(buffer, adjustCase(curr))
+		} else if curr != 0 {
+			buffer = append(buffer, adjustCase(curr))
+		}
+		prev = curr
+		curr = next
+	}
+
+	if len(s) > 0 {
+		if isUpper(curr) && isLower(prev) && prev != 0 {
+			buffer = append(buffer, delimiter)
+		}
+		buffer = append(buffer, adjustCase(curr))
+	}
+
+	return string(buffer)
+}

snake_test.go

@@ -31,3 +31,26 @@ func TestSnakeCase(t *testing.T) {
 		assert.Equal(t, snake, converted)
 	}
 }
+
+func TestUpperSnakeCase(t *testing.T) {
+	data := map[string]string{
+		"":                           "",
+		"F":                          "F",
+		"Foo":                        "FOO",
+		"FooB":                       "FOO_B",
+		"FooID":                      "FOO_ID",
+		" FooBar\t":                  "FOO_BAR",
+		"HTTPStatusCode":             "HTTP_STATUS_CODE",
+		"ParseURL.DoParse":           "PARSE_URL.DO_PARSE",
+		"Convert Space":              "CONVERT_SPACE",
+		"Convert-dash":               "CONVERT_DASH",
+		"Skip___MultipleUnderscores": "SKIP_MULTIPLE_UNDERSCORES",
+		"Skip   MultipleSpaces":      "SKIP_MULTIPLE_SPACES",
+		"Skip---MultipleDashes":      "SKIP_MULTIPLE_DASHES",
+	}
+
+	for camel, snake := range data {
+		converted := UpperSnakeCase(camel)
+		assert.Equal(t, snake, converted)
+	}
+}