From ea0f96a8c0ca38bdfefefc37b06673c0b33bdcda Mon Sep 17 00:00:00 2001
From: dudaodong <lanliddd.2007@163.com>
Date: Mon, 30 Jan 2023 16:56:33 +0800
Subject: [PATCH] feat: add Skip for stream

---
 stream/stream.go      | 33 ++++++++++++++++++++++++++++++++-
 stream/stream_test.go | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/stream/stream.go b/stream/stream.go
index 4ac92b4..c694aaa 100644
--- a/stream/stream.go
+++ b/stream/stream.go
@@ -28,7 +28,7 @@ import (
 // 	Min(less func(a, b T) bool) (T, bool)
 
 // 	Limit(maxSize int) StreamI[T]
-// 	Skip(n int64) StreamI[T]
+// 	Skip(n int) StreamI[T]
 
 // 	AllMatch(predicate func(item T) bool) bool
 // 	AnyMatch(predicate func(item T) bool) bool
@@ -158,6 +158,37 @@ func (s stream[T]) Map(mapper func(item T) T) stream[T] {
 	return FromSlice(source)
 }
 
+// Peek returns a stream consisting of the elements of this stream, additionally performing the provided action on each element as elements are consumed from the resulting stream.
+func (s stream[T]) Peek(consumer func(item T)) stream[T] {
+	for _, v := range s.source {
+		consumer(v)
+	}
+
+	return s
+}
+
+// Skip Returns a stream consisting of the remaining elements of this stream after discarding the first n elements of the stream. If this stream contains fewer than n elements then an empty stream will be returned.
+func (s stream[T]) Skip(n int) stream[T] {
+	if n <= 0 {
+		return s
+	}
+
+	source := make([]T, 0)
+	l := len(s.source)
+
+	if n > l {
+		return FromSlice(source)
+	}
+
+	// source = make([]T, l-n+1, l-n+1)
+
+	for i := n; i < l; i++ {
+		source = append(source, s.source[i])
+	}
+
+	return FromSlice(source)
+}
+
 // Count returns the count of elements in the stream.
 func (s stream[T]) Count() int {
 	return len(s.source)
diff --git a/stream/stream_test.go b/stream/stream_test.go
index 271e46f..4fb5e38 100644
--- a/stream/stream_test.go
+++ b/stream/stream_test.go
@@ -1,6 +1,7 @@
 package stream
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/duke-git/lancet/v2/internal"
@@ -124,3 +125,34 @@ func TestStream_Map(t *testing.T) {
 
 	assert.Equal([]int{2, 3, 4}, s.ToSlice())
 }
+
+func TestStream_Peek(t *testing.T) {
+	assert := internal.NewAssert(t, "TestStream_Peek")
+
+	stream := FromSlice([]int{1, 2, 3, 4, 5, 6})
+
+	result := []string{}
+	stream = stream.Filter(func(n int) bool {
+		return n <= 3
+	}).Peek(func(n int) {
+		result = append(result, fmt.Sprint("current: ", n))
+	})
+
+	assert.Equal([]int{1, 2, 3}, stream.ToSlice())
+	assert.Equal([]string{
+		"current: 1", "current: 2", "current: 3",
+	}, result)
+}
+
+func TestStream_Skip(t *testing.T) {
+	assert := internal.NewAssert(t, "TestStream_Peek")
+
+	stream := FromSlice([]int{1, 2, 3, 4, 5, 6})
+
+	s1 := stream.Skip(-1)
+	s2 := stream.Skip(0)
+	// s2 := stream.Skip(0)
+
+	assert.Equal([]int{1, 2, 3, 4, 5, 6}, s1.ToSlice())
+	assert.Equal([]int{1, 2, 3, 4, 5, 6}, s2.ToSlice())
+}