doc: add doc for Pad function

docs/strutil.md

@@ -33,8 +33,9 @@ import (
 -   [UpperKebabCase](#UpperKebabCase)
 -   [LowerFirst](#LowerFirst)
 -   [UpperFirst](#UpperFirst)
--   [PadEnd](#PadEnd)
+-   [Pad](#Pad)
 -   [PadStart](#PadStart)
+-   [PadEnd](#PadEnd)
 -   [Reverse](#Reverse)
 -   [SnakeCase](#SnakeCase)
 -   [UpperSnakeCase](#UpperSnakeCase)
@@ -449,6 +450,51 @@ func main() {
 }
 ```
 
+### <span id="Pad">Pad</span>
+
+<p>Pads string on the left and right side if it's shorter than size.</p>
+
+<b>Signature:</b>
+
+```go
+func Pad(source string, size int, padStr string) string
+```
+
+<b>Example:</b>
+
+```go
+import (
+    "fmt"
+    "github.com/duke-git/lancet/v2/strutil"
+)
+
+func main() {
+    result1 := strutil.Pad("foo", 1, "bar")
+	result2 := strutil.Pad("foo", 2, "bar")
+	result3 := strutil.Pad("foo", 3, "bar")
+	result4 := strutil.Pad("foo", 4, "bar")
+	result5 := strutil.Pad("foo", 5, "bar")
+	result6 := strutil.Pad("foo", 6, "bar")
+	result7 := strutil.Pad("foo", 7, "bar")
+
+	fmt.Println(result1)
+	fmt.Println(result2)
+	fmt.Println(result3)
+	fmt.Println(result4)
+	fmt.Println(result5)
+	fmt.Println(result6)
+	fmt.Println(result7)
+	// Output:
+	// foo
+	// foo
+	// foo
+	// foob
+	// bfoob
+	// bfooba
+	// bafooba
+}
+```
+
 ### <span id="PadEnd">PadEnd</span>
 
 <p>Pads string on the right side if it's shorter than size.</p>

docs/strutil_zh-CN.md

@@ -449,6 +449,51 @@ func main() {
 }
 ```
 
+### <span id="Pad">Pad</span>
+
+<p>如果字符串长度短于size，则在左右两侧填充字符串。</p>
+
+<b>函数签名:</b>
+
+```go
+func Pad(source string, size int, padStr string) string
+```
+
+<b>示例:</b>
+
+```go
+import (
+    "fmt"
+    "github.com/duke-git/lancet/v2/strutil"
+)
+
+func main() {
+    result1 := strutil.Pad("foo", 1, "bar")
+	result2 := strutil.Pad("foo", 2, "bar")
+	result3 := strutil.Pad("foo", 3, "bar")
+	result4 := strutil.Pad("foo", 4, "bar")
+	result5 := strutil.Pad("foo", 5, "bar")
+	result6 := strutil.Pad("foo", 6, "bar")
+	result7 := strutil.Pad("foo", 7, "bar")
+
+	fmt.Println(result1)
+	fmt.Println(result2)
+	fmt.Println(result3)
+	fmt.Println(result4)
+	fmt.Println(result5)
+	fmt.Println(result6)
+	fmt.Println(result7)
+	// Output:
+	// foo
+	// foo
+	// foo
+	// foob
+	// bfoob
+	// bfooba
+	// bafooba
+}
+```
+
 ### <span id="PadEnd">PadEnd</span>
 
 <p>如果字符串长度短于size，则在右侧填充字符串。</p>

strutil/string.go

@@ -67,44 +67,25 @@ func LowerFirst(s string) string {
 	return string(r) + s[size:]
 }
 
-// PadEnd pads string on the right side if it's shorter than size.
+// PadStart pads string on the left and right side if it's shorter than size.
 // Padding characters are truncated if they exceed size.
-// Play: https://go.dev/play/p/9xP8rN0vz--
-func PadEnd(source string, size int, padStr string) string {
-	len1 := len(source)
-	len2 := len(padStr)
-
-	if len1 >= size {
-		return source
-	}
-
-	fill := ""
-	if len2 >= size-len1 {
-		fill = padStr[0 : size-len1]
-	} else {
-		fill = strings.Repeat(padStr, size-len1)
-	}
-	return source + fill[0:size-len1]
+// Play: todo
+func Pad(source string, size int, padStr string) string {
+	return padAtPosition(source, size, padStr, 0)
 }
 
 // PadStart pads string on the left side if it's shorter than size.
 // Padding characters are truncated if they exceed size.
 // Play: https://go.dev/play/p/xpTfzArDfvT
 func PadStart(source string, size int, padStr string) string {
-	len1 := len(source)
-	len2 := len(padStr)
+	return padAtPosition(source, size, padStr, 1)
+}
 
-	if len1 >= size {
-		return source
-	}
-
-	fill := ""
-	if len2 >= size-len1 {
-		fill = padStr[0 : size-len1]
-	} else {
-		fill = strings.Repeat(padStr, size-len1)
-	}
-	return fill[0:size-len1] + source
+// PadEnd pads string on the right side if it's shorter than size.
+// Padding characters are truncated if they exceed size.
+// Play: https://go.dev/play/p/9xP8rN0vz--
+func PadEnd(source string, size int, padStr string) string {
+	return padAtPosition(source, size, padStr, 2)
 }
 
 // KebabCase coverts string to kebab-case, non letters and numbers will be ignored.

strutil/string_example_test.go

@@ -186,6 +186,33 @@ func ExampleUpperFirst() {
 	// Bar大
 }
 
+func ExamplePad() {
+	result1 := Pad("foo", 1, "bar")
+	result2 := Pad("foo", 2, "bar")
+	result3 := Pad("foo", 3, "bar")
+	result4 := Pad("foo", 4, "bar")
+	result5 := Pad("foo", 5, "bar")
+	result6 := Pad("foo", 6, "bar")
+	result7 := Pad("foo", 7, "bar")
+
+	fmt.Println(result1)
+	fmt.Println(result2)
+	fmt.Println(result3)
+	fmt.Println(result4)
+	fmt.Println(result5)
+	fmt.Println(result6)
+	fmt.Println(result7)
+
+	// Output:
+	// foo
+	// foo
+	// foo
+	// foob
+	// bfoob
+	// bfooba
+	// bafooba
+}
+
 func ExamplePadEnd() {
 	result1 := PadEnd("foo", 1, "bar")
 	result2 := PadEnd("foo", 2, "bar")

strutil/string_internal.go

@@ -98,3 +98,40 @@ func toUpperAll(rs []rune) []rune {
 	}
 	return rs
 }
+
+// padWithPosition pads string
+func padAtPosition(str string, length int, padStr string, position int) string {
+	if len(str) >= length {
+		return str
+	}
+
+	if padStr == "" {
+		padStr = " "
+	}
+
+	length = length - len(str)
+	startPadLen := 0
+	if position == 0 {
+		startPadLen = length / 2
+	} else if position == 1 {
+		startPadLen = length
+	}
+	endPadLen := length - startPadLen
+
+	charLen := len(padStr)
+	leftPad := ""
+	cur := 0
+	for cur < startPadLen {
+		leftPad += string(padStr[cur%charLen])
+		cur++
+	}
+
+	cur = 0
+	rightPad := ""
+	for cur < endPadLen {
+		rightPad += string(padStr[cur%charLen])
+		cur++
+	}
+
+	return leftPad + str + rightPad
+}

strutil/string_test.go

@@ -168,9 +168,19 @@ func TestLowerFirst(t *testing.T) {
 	}
 }
 
+func TestPad(t *testing.T) {
+	assert := internal.NewAssert(t, "TestPad")
+
+	assert.Equal("a ", Pad("a", 2, ""))
+	assert.Equal("a", Pad("a", 1, "b"))
+	assert.Equal("ab", Pad("a", 2, "b"))
+	assert.Equal("mabcdm", Pad("abcd", 6, "m"))
+}
+
 func TestPadEnd(t *testing.T) {
 	assert := internal.NewAssert(t, "TestPadEnd")
 
+	assert.Equal("a ", PadEnd("a", 2, " "))
 	assert.Equal("a", PadEnd("a", 1, "b"))
 	assert.Equal("ab", PadEnd("a", 2, "b"))
 	assert.Equal("abcdmn", PadEnd("abcd", 6, "mno"))