From 15ea874a75c253aa979d2cb8423fbe05e41a2158 Mon Sep 17 00:00:00 2001
From: Patrick O'brien <nullbio@users.noreply.github.com>
Date: Mon, 8 Aug 2016 09:34:11 +1000
Subject: [PATCH] Add SnakeCase

---
 strmangle/strmangle.go      | 17 +++++++++++++++++
 strmangle/strmangle_test.go | 29 +++++++++++++++++++++++++++++
 templates.go                |  3 ++-
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/strmangle/strmangle.go b/strmangle/strmangle.go
index 3fdde19..7890d9e 100644
--- a/strmangle/strmangle.go
+++ b/strmangle/strmangle.go
@@ -9,6 +9,7 @@ import (
 	"math"
 	"regexp"
 	"strings"
+	"unicode"
 
 	"github.com/jinzhu/inflection"
 )
@@ -138,6 +139,22 @@ func CamelCase(name string) string {
 	return strings.Join(splits, "")
 }
 
+// SnakeCase converts TitleCase variable names to snake_case format.
+func SnakeCase(name string) string {
+	runes := []rune(name)
+	length := len(runes)
+
+	var out []rune
+	for i := 0; i < length; i++ {
+		if i > 0 && unicode.IsUpper(runes[i]) && ((i+1 < length && unicode.IsLower(runes[i+1])) || unicode.IsLower(runes[i-1]) || unicode.IsDigit(runes[i-1])) {
+			out = append(out, '_')
+		}
+		out = append(out, unicode.ToLower(runes[i]))
+	}
+
+	return string(out)
+}
+
 // MakeStringMap converts a map[string]string into the format:
 // "key": "value", "key": "value"
 func MakeStringMap(types map[string]string) string {
diff --git a/strmangle/strmangle_test.go b/strmangle/strmangle_test.go
index 5efa6ae..1f7c231 100644
--- a/strmangle/strmangle_test.go
+++ b/strmangle/strmangle_test.go
@@ -185,6 +185,35 @@ func TestCamelCase(t *testing.T) {
 	}
 }
 
+func TestSnakeCase(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		In  string
+		Out string
+	}{
+		{"ID", "id"},
+		{"ID9", "id9"},
+		{"Thing", "thing"},
+		{"Thing92", "thing92"},
+		{"ThingGUID", "thing_guid"},
+		{"ThingGUIDTwo", "thing_guid_two"},
+		{"ThingStuff", "thing_stuff"},
+		{"ThingStuff1GUID", "thing_stuff1_guid"},
+		{"ThingStuff12GUID", "thing_stuff12_guid"},
+		{"ThingStuff123GUID", "thing_stuff123_guid"},
+		{"GUIDThingStuffID123", "guid_thing_stuff_id123"},
+		{"GUIDThingStuffID12", "guid_thing_stuff_id12"},
+		{"GUIDThingStuffID1", "guid_thing_stuff_id1"},
+	}
+
+	for i, test := range tests {
+		if out := SnakeCase(test.In); out != test.Out {
+			t.Errorf("%d) Want: %q, got %q", i, test.Out, out)
+		}
+	}
+}
+
 func TestMakeStringMap(t *testing.T) {
 	t.Parallel()
 
diff --git a/templates.go b/templates.go
index f266236..6aa74d5 100644
--- a/templates.go
+++ b/templates.go
@@ -119,6 +119,7 @@ var templateStringMappers = map[string]func(string) string{
 	"toUpper":   strings.ToUpper,
 	"titleCase": strmangle.TitleCase,
 	"camelCase": strmangle.CamelCase,
+	"snakeCase": strmangle.SnakeCase,
 }
 
 // templateFunctions is a map of all the functions that get passed into the
@@ -168,7 +169,7 @@ var templateFunctions = template.FuncMap{
 	"filterColumnsByDefault":       bdb.FilterColumnsByDefault,
 	"filterColumnsBySimpleDefault": bdb.FilterColumnsBySimpleDefault,
 	"filterColumnsByAutoIncrement": bdb.FilterColumnsByAutoIncrement,
-	"filterColumnsByValidated":      bdb.FilterColumnsByValidated,
+	"filterColumnsByValidated":     bdb.FilterColumnsByValidated,
 	"autoIncPrimaryKey":            bdb.AutoIncPrimaryKey,
 	"sqlColDefinitions":            bdb.SQLColDefinitions,
 	"sqlColDefStrings":             bdb.SQLColDefStrings,