From e856ec18e1e287617cf5d0264fcc1cc3fd6ca9c7 Mon Sep 17 00:00:00 2001
From: milarin <milaring@proton.me>
Date: Thu, 27 Jul 2023 22:09:41 +0200
Subject: [PATCH] implemented Push and Pop

---
 errors.go      |  1 +
 go.mod         |  3 +++
 go.sum         |  4 ++++
 reader.go      | 61 ++++++++++++++++++++++++++++++++++++++++++++------
 reader_test.go | 10 ++++++++-
 5 files changed, 71 insertions(+), 8 deletions(-)

diff --git a/errors.go b/errors.go
index a5a653a..88913c0 100644
--- a/errors.go
+++ b/errors.go
@@ -6,5 +6,6 @@ import (
 
 var (
 	ErrNothingToUnread = adverr.NewErrTmpl("ErrNothingToUnread", "Unreading failed because there wasn't any Read yet")
+	ErrPopFailed       = adverr.NewErrTmpl("ErrPopFailed", "stack cannot be popped. It was never pushed")
 	ErrNoMoreValues    = adverr.NewErrTmpl("ErrNoMoreValues", "source does not have any more values")
 )
diff --git a/go.mod b/go.mod
index e591a7f..b774133 100644
--- a/go.mod
+++ b/go.mod
@@ -5,4 +5,7 @@ go 1.20
 require (
 	git.milar.in/milarin/adverr v1.1.0
 	git.milar.in/milarin/ds v0.0.2
+	git.milar.in/milarin/slices v0.0.8
 )
+
+require git.milar.in/milarin/gmath v0.0.3 // indirect
diff --git a/go.sum b/go.sum
index bb49ff3..cabd037 100644
--- a/go.sum
+++ b/go.sum
@@ -2,3 +2,7 @@ git.milar.in/milarin/adverr v1.1.0 h1:jD9WnOvs40lfMhvqQ7cllOaRJNBMWr1f07/s9jAadp
 git.milar.in/milarin/adverr v1.1.0/go.mod h1:joU9sBb7ySyNv4SpTXB0Z4o1mjXsArBw4N27wjgzj9E=
 git.milar.in/milarin/ds v0.0.2 h1:vCA3mDxZUNfvHpzrdz7SeBUKiPn74NTopo915IUG7I0=
 git.milar.in/milarin/ds v0.0.2/go.mod h1:HJK7QERcRvV9j7xzEocrKUtW+1q4JB1Ly4Bj54chfwI=
+git.milar.in/milarin/gmath v0.0.3 h1:ii6rKNItS55O/wtIFhD1cTN2BMwDZjTBmiOocKURvxM=
+git.milar.in/milarin/gmath v0.0.3/go.mod h1:HDLftG5RLpiNGKiIWh+O2G1PYkNzyLDADO8Cd/1abiE=
+git.milar.in/milarin/slices v0.0.8 h1:qN9TE3tkArdTixMKSnwvNPcApwAjxpLVwA5a9k1rm2s=
+git.milar.in/milarin/slices v0.0.8/go.mod h1:qMhdtMnfWswc1rHpwgNw33lB84aNEkdBn5BDiYA+G3k=
diff --git a/reader.go b/reader.go
index 85888e8..c6c07d2 100644
--- a/reader.go
+++ b/reader.go
@@ -1,10 +1,15 @@
 package anyreader
 
-import "git.milar.in/milarin/ds"
+import (
+	"git.milar.in/milarin/ds"
+	"git.milar.in/milarin/slices"
+)
 
 type Reader[T any] struct {
-	buf ds.Stack[T]
-	src func() (T, error)
+	buf     ds.Stack[T]
+	indices ds.Stack[uint64]
+	index   uint64
+	src     func() (T, error)
 }
 
 func NewReaderFromSlice[T any](s []T) *Reader[T] {
@@ -17,8 +22,10 @@ func NewReaderFromFunc[T any](src func() T) *Reader[T] {
 
 func NewReaderFromErrorFunc[T any](src func() (T, error)) *Reader[T] {
 	return &Reader[T]{
-		src: src,
-		buf: ds.NewArrayStack[T](),
+		src:     src,
+		buf:     ds.NewArrayStack[T](),
+		index:   0,
+		indices: ds.NewArrayStack[uint64](),
 	}
 }
 
@@ -26,6 +33,7 @@ func (r *Reader[T]) Read() (T, error) {
 	v, err := r.src()
 	if err == nil {
 		r.buf.Push(v)
+		r.index++
 	}
 	return v, err
 }
@@ -36,6 +44,7 @@ func (r *Reader[T]) Unread() error {
 	}
 
 	v := r.buf.Pop()
+	r.index--
 
 	returned := false
 	oldSrc := r.src
@@ -114,6 +123,44 @@ func (r *Reader[T]) Expect(f ...func(T) bool) (bool, error) {
 	return findFirstTrue(value, f), nil
 }
 
-func (r *Reader[T]) Commit() {
-	r.buf.Clear()
+func (r *Reader[T]) Push() {
+	r.indices.Push(r.index)
+}
+
+func (r *Reader[T]) Pop() ([]T, error) {
+	if r.indices.Empty() {
+		return nil, ErrPopFailed.New()
+	}
+
+	lastIndex := r.indices.Pop()
+	currentIndex := r.index
+	if lastIndex < currentIndex {
+		values := make([]T, 0, int(currentIndex-lastIndex))
+		for i := 0; i < int(currentIndex-lastIndex); i++ {
+			err := r.Unread()
+			if err != nil {
+				return nil, err
+			}
+
+			value, err := r.Peek()
+			if err != nil {
+				return nil, err
+			}
+
+			values = append(values, value)
+		}
+		return slices.Reverse(values), nil
+	} else if lastIndex > currentIndex {
+		values := make([]T, 0, int(lastIndex-currentIndex))
+		for i := 0; i < int(lastIndex-currentIndex); i++ {
+			value, err := r.Read()
+			if err != nil {
+				return nil, err
+			}
+			values = append(values, value)
+		}
+		return values, nil
+	}
+
+	return []T{}, nil
 }
diff --git a/reader_test.go b/reader_test.go
index 805a60f..d00fb0a 100644
--- a/reader_test.go
+++ b/reader_test.go
@@ -8,6 +8,14 @@ import (
 func TestReader(t *testing.T) {
 	r := NewReaderFromSlice([]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
 	fmt.Println(r.Read())
-	r.Unread()
+	fmt.Println(r.Read())
+
+	r.Push()
+
+	fmt.Println(r.Unread())
+	fmt.Println(r.Unread())
+
+	fmt.Println(r.Pop())
+
 	fmt.Println(r.Read())
 }