refs #24. camelCaseToUnderScore can handle more special cases.

Includes:

* A_B => a_b
* _A  => _a

facebook_test.go

@@ -1286,8 +1286,9 @@ func TestCamelCaseToUnderScore(t *testing.T) {
 		"HTTPServer":         "http_server",
 		"NoHTTPS":            "no_https",
 		"Wi_thF":             "wi_th_f",
-		"_AnotherTES_TCaseP": "__another_te_s__t_case_p",
-		"ALL": "all",
+		"_AnotherTES_TCaseP": "_another_tes_t_case_p",
+		"ALL":                "all",
+		"UserID":             "user_id",
 	}
 
 	for k, v := range cases {

misc.go

@@ -14,32 +14,39 @@ import (
 	"unicode/utf8"
 )
 
-func camelCaseToUnderScore(name string) string {
+func camelCaseToUnderScore(str string) string {
+	if len(str) == 0 {
+		return ""
+	}
+
 	buf := &bytes.Buffer{}
-	var r0, r1 rune
+	var prev, r0, r1 rune
 	var size int
 
-	for len(name) > 0 {
-		r0, size = utf8.DecodeRuneInString(name)
-		name = name[size:]
+	r0 = '_'
+
+	for len(str) > 0 {
+		prev = r0
+		r0, size = utf8.DecodeRuneInString(str)
+		str = str[size:]
 
 		switch {
 		case r0 == utf8.RuneError:
-			buf.WriteByte(byte(name[0]))
+			buf.WriteByte(byte(str[0]))
 
 		case unicode.IsUpper(r0):
-			if buf.Len() > 0 {
+			if prev != '_' {
 				buf.WriteRune('_')
 			}
 
 			buf.WriteRune(unicode.ToLower(r0))
 
-			if len(name) == 0 {
+			if len(str) == 0 {
 				break
 			}
 
-			r0, size = utf8.DecodeRuneInString(name)
-			name = name[size:]
+			r0, size = utf8.DecodeRuneInString(str)
+			str = str[size:]
 
 			if !unicode.IsUpper(r0) {
 				buf.WriteRune(r0)
@@ -50,32 +57,44 @@ func camelCaseToUnderScore(name string) string {
 			// it's designed to convert `HTTPServer` to `http_server`.
 			// if there are more than 2 adjacent upper case characters in a word,
 			// treat them as an abbreviation plus a normal word.
-			for len(name) > 0 {
+			for len(str) > 0 {
 				r1 = r0
-				r0, size = utf8.DecodeRuneInString(name)
-				name = name[size:]
+				r0, size = utf8.DecodeRuneInString(str)
+				str = str[size:]
 
 				if r0 == utf8.RuneError {
 					buf.WriteRune(unicode.ToLower(r1))
-					buf.WriteByte(byte(name[0]))
+					buf.WriteByte(byte(str[0]))
 					break
 				}
 
 				if !unicode.IsUpper(r0) {
-					buf.WriteRune('_')
-					buf.WriteRune(unicode.ToLower(r1))
-					buf.WriteRune(r0)
+					if r0 == '_' || r0 == ' ' || r0 == '-' {
+						r0 = '_'
+
+						buf.WriteRune(unicode.ToLower(r1))
+					} else {
+						buf.WriteRune('_')
+						buf.WriteRune(unicode.ToLower(r1))
+						buf.WriteRune(r0)
+					}
+
 					break
 				}
 
 				buf.WriteRune(unicode.ToLower(r1))
 			}
 
-			if len(name) == 0 {
+			if len(str) == 0 || r0 == '_' {
 				buf.WriteRune(unicode.ToLower(r0))
+				break
 			}
 
 		default:
+			if r0 == ' ' || r0 == '-' {
+				r0 = '_'
+			}
+
 			buf.WriteRune(r0)
 		}
 	}