not elegant but solves all issues

Author: EvilLord666

formatter.go

@@ -55,6 +55,13 @@ func Format(template string, args ...any) string {
 				continue
 			}
 			// find end of placeholder
+			// process empty pair - {}
+			if template[i+1] == '}' {
+				i++
+				formattedStr.WriteString("{}")
+				continue
+			}
+			// process non-empty placeholder
 			j = i + 2
 			for {
 				if j >= templateLen {
@@ -117,14 +124,9 @@ func Format(template string, args ...any) string {
 					strVal := getItemAsStr(&args[argNumber], &argFormatOptions)
 					formattedStr.WriteString(strVal)
 				} else {
-					if argNumberStr != "" {
-						formattedStr.WriteByte('{')
-						formattedStr.WriteString(argNumberStr)
-						formattedStr.WriteByte('}')
-					} else {
-						// complicated case when we have brackets in line and open line at the end
-						formattedStr.WriteByte('{')
-					}
+					formattedStr.WriteByte('{')
+					formattedStr.WriteString(argNumberStr)
+					formattedStr.WriteByte('}')
 				}
 				i = j
 			}
@@ -170,10 +172,18 @@ func FormatComplex(template string, args map[string]any) string {
 				break
 			}
 
-			if template[i+1] == '{' { // todo: umv: this not considering {{0}}
+			if template[i+1] == '{' {
 				formattedStr.WriteByte('{')
 				continue
 			}
+			// find end of placeholder
+			// process empty pair - {}
+			if template[i+1] == '}' {
+				i++
+				formattedStr.WriteString("{}")
+				continue
+			}
+			// process non-empty placeholder
 
 			// find end of placeholder
 			j = i + 2
@@ -215,14 +225,12 @@ func FormatComplex(template string, args map[string]any) string {
 					strVal := getItemAsStr(&arg, &argFormatOptions)
 					formattedStr.WriteString(strVal)
 				} else {
-					if argNumberStr != "" {
-						formattedStr.WriteByte('{')
-						formattedStr.WriteString(argNumberStr)
-						formattedStr.WriteByte('}')
-					} else {
-						// complicated case when we have brackets in line and open line at the end
-						formattedStr.WriteByte('{')
-					}
+					formattedStr.WriteByte('{')
+
+					//if argNumberStr != "" {
+					formattedStr.WriteString(argNumberStr)
+					formattedStr.WriteByte('}')
+					//}
 				}
 				i = j
 			}

formatter_test.go

@@ -129,6 +129,17 @@ func TestFormat(t *testing.T) {
 			args:     []any{},
 			expected: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}) }",
 		},
+
+		"no bracket at the end of line with {} inside": {
+			template: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}) ",
+			args:     []any{},
+			expected: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}) ",
+		},
+		"open bracket at the end of line of go line with multiple {} inside": {
+			template: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}, additionalData interface{}) {",
+			args:     []any{},
+			expected: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}, additionalData interface{}) {",
+		},
 	} {
 		t.Run(name, func(t *testing.T) {
 			assert.Equal(t, test.expected, stringFormatter.Format(test.template, test.args...))
@@ -219,6 +230,12 @@ func TestFormatComplex(t *testing.T) {
 			expected: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}) {",
 		},
 
+		"open bracket at the end of line of go line with multiple {} inside": {
+			template: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}, additionalData interface{}) {",
+			args:     map[string]any{},
+			expected: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}, additionalData interface{}) {",
+		},
+
 		"close bracket at the end of line of go line with {} inside": {
 			template: "func afterHandle(respWriter *http.ResponseWriter, statusCode int, data interface{}) }",
 			args:     map[string]any{},