From 2d07e6c6eeda93b6a2b81ee1e9253068e3ac5a6b Mon Sep 17 00:00:00 2001
From: dennis <zhishun.xu@gmail.com>
Date: Mon, 30 Oct 2023 11:38:38 +0800
Subject: [PATCH] Add: StringUtils.Substring

---
 StringUtils.go      | 33 +++++++++++++++++++++++++++++
 StringUtils_test.go | 51 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+)
 create mode 100644 StringUtils_test.go

diff --git a/StringUtils.go b/StringUtils.go
index 07bde77..1fc82f7 100644
--- a/StringUtils.go
+++ b/StringUtils.go
@@ -33,3 +33,36 @@ func (s *StringUtils) LeftPad(str string, size int, padStr string) string {
 
 	return strings.Repeat(padStr, padCount) + str
 }
+
+func (s *StringUtils) Substring(str string, start, end int) string {
+	if str == "" {
+		return str
+	}
+
+	runes := []rune(str)
+
+	if end < 0 {
+		end = len(runes) + end
+	}
+	if start < 0 {
+		start = len(runes) + start
+	}
+
+	if end > len(str) {
+		end = len(str)
+	}
+
+	if start > end {
+		return EMPTY
+	}
+
+	if start < 0 {
+		start = 0
+	}
+
+	if end < 0 {
+		end = 0
+	}
+
+	return string(runes[start:end])
+}
diff --git a/StringUtils_test.go b/StringUtils_test.go
new file mode 100644
index 0000000..4ede209
--- /dev/null
+++ b/StringUtils_test.go
@@ -0,0 +1,51 @@
+package golanghelper_test
+
+import (
+	"testing"
+
+	"gitlab-ce.niaulang.com/niau-lang/golanghelper"
+)
+
+func TestSubstring(t *testing.T) {
+	stringUtils := golanghelper.StringUtils{}
+
+	s := stringUtils.Substring("", 0, 0)
+	if s != "" {
+		t.Errorf("預期的值為空字串, 卻回傳 %v", s)
+	}
+
+	s = stringUtils.Substring("abc", 0, 2)
+	if s != "ab" {
+		t.Errorf("預期的值為 ab, 卻回傳 %v", s)
+	}
+
+	s = stringUtils.Substring("abc", 2, 0)
+	if s != "" {
+		t.Errorf("預期的值為空字串, 卻回傳 %v", s)
+	}
+
+	s = stringUtils.Substring("abc", 2, 4)
+	if s != "c" {
+		t.Errorf("預期的值為 c, 卻回傳 %v", s)
+	}
+
+	s = stringUtils.Substring("abc", 4, 6)
+	if s != "" {
+		t.Errorf("預期的值為空字串, 卻回傳 %v", s)
+	}
+
+	s = stringUtils.Substring("abc", 2, 2)
+	if s != "" {
+		t.Errorf("預期的值為 ab, 卻回傳 %v", s)
+	}
+
+	s = stringUtils.Substring("abc", -2, -1)
+	if s != "b" {
+		t.Errorf("預期的值為 b, 卻回傳 %v", s)
+	}
+
+	s = stringUtils.Substring("abc", -4, 2)
+	if s != "ab" {
+		t.Errorf("預期的值為 ab, 卻回傳 %v", s)
+	}
+}