From f35f8da02f23797ef28e525f15e1b88d5b5e288e Mon Sep 17 00:00:00 2001
From: Vojtech Vitek <vojtech.vitek@visioncritical.com>
Date: Tue, 5 Mar 2019 18:59:47 -0500
Subject: [PATCH] Implement CamelCase via new state machine

---
 helpers.go      | 64 +++++++++++++++++++++++++++++++++++++++++++++++++
 helpers_test.go | 25 +++++++++++++++++++
 2 files changed, 89 insertions(+)
 create mode 100644 helpers.go
 create mode 100644 helpers_test.go

diff --git a/helpers.go b/helpers.go
new file mode 100644
index 0000000..c8f47ef
--- /dev/null
+++ b/helpers.go
@@ -0,0 +1,64 @@
+package goose
+
+import (
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+type camelSnakeStateMachine int
+
+const (
+	begin         camelSnakeStateMachine = iota // 0
+	firstAlphaNum                               // 1
+	alphaNum                                    // 2
+	delimiter                                   // 3
+)
+
+func (s camelSnakeStateMachine) next(r rune) camelSnakeStateMachine {
+	switch s {
+	case begin:
+		if isAlphaNum(r) {
+			return firstAlphaNum
+		}
+	case firstAlphaNum:
+		if isAlphaNum(r) {
+			return alphaNum
+		} else {
+			return delimiter
+		}
+	case alphaNum:
+		if !isAlphaNum(r) {
+			return delimiter
+		}
+	case delimiter:
+		if isAlphaNum(r) {
+			return firstAlphaNum
+		} else {
+			return begin
+		}
+	}
+	return s
+}
+
+func lowerCamelCase(str string) string {
+	var b strings.Builder
+
+	stateMachine := begin
+	for i := 0; i < len(str); {
+		r, size := utf8.DecodeRuneInString(str[i:])
+		i += size
+		stateMachine = stateMachine.next(r)
+		switch stateMachine {
+		case firstAlphaNum:
+			b.WriteRune(unicode.ToUpper(r))
+		case alphaNum:
+			b.WriteRune(unicode.ToLower(r))
+		}
+	}
+	return b.String()
+}
+
+func isAlphaNum(r rune) bool {
+	return unicode.IsLetter(r) || unicode.IsNumber(r)
+}
diff --git a/helpers_test.go b/helpers_test.go
new file mode 100644
index 0000000..bf8a3d7
--- /dev/null
+++ b/helpers_test.go
@@ -0,0 +1,25 @@
+package goose
+
+import (
+	"testing"
+)
+
+func TestCamelSnake(t *testing.T) {
+	tt := []struct {
+		in    string
+		camel string
+		snake string
+	}{
+		{in: "Add updated_at to users table", camel: "addUpdatedAtToUsersTable", snake: "add_updated_at_to_users_table"},
+		{in: "$()&^%(_--crazy__--input$)", camel: "crazyInput", snake: "crazy_input"},
+	}
+
+	for _, test := range tt {
+		if got := lowerCamelCase(test.in); got != test.camel {
+			t.Errorf("unexpected lower camel for input(%q), got %q, want %q", test.in, got, test.camel)
+		}
+		// if got := snake(test.in); got != test.snake {
+		// 	t.Error("unexpected snake for input(%q), got %q, want %q", test.in, got, test.snake)
+		// }
+	}
+}