From af840a50199fc6ce115c613e7370b0da97ddcdac Mon Sep 17 00:00:00 2001
From: milarin <milaring@proton.me>
Date: Mon, 7 Aug 2023 19:51:10 +0200
Subject: [PATCH] Push and Pop added

---
 errors.go |  1 +
 go.mod    |  3 +++
 go.sum    |  8 +++----
 reader.go | 64 ++++++++++++++++++++++++++++++++++++++++++++++---------
 4 files changed, 62 insertions(+), 14 deletions(-)

diff --git a/errors.go b/errors.go
index 7152e3a..1322c3d 100644
--- a/errors.go
+++ b/errors.go
@@ -6,4 +6,5 @@ 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")
 )
diff --git a/go.mod b/go.mod
index b1bfac8..f4b54ef 100644
--- a/go.mod
+++ b/go.mod
@@ -5,4 +5,7 @@ go 1.19
 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 010c479..cabd037 100644
--- a/go.sum
+++ b/go.sum
@@ -1,8 +1,8 @@
 git.milar.in/milarin/adverr v1.1.0 h1:jD9WnOvs40lfMhvqQ7cllOaRJNBMWr1f07/s9jAadp0=
 git.milar.in/milarin/adverr v1.1.0/go.mod h1:joU9sBb7ySyNv4SpTXB0Z4o1mjXsArBw4N27wjgzj9E=
-git.milar.in/milarin/ds v0.0.0-20230120204927-7dc44b9cd222 h1:r7gcMqltPqk9U2/+LzEN5dooZ5wiQ8C7SI/nK6T0KjA=
-git.milar.in/milarin/ds v0.0.0-20230120204927-7dc44b9cd222/go.mod h1:HJK7QERcRvV9j7xzEocrKUtW+1q4JB1Ly4Bj54chfwI=
-git.milar.in/milarin/ds v0.0.1 h1:ov4Rp+QiB3xtmV0a4eC+LluxWEOvbykgW+wCchYEp9o=
-git.milar.in/milarin/ds v0.0.1/go.mod h1:HJK7QERcRvV9j7xzEocrKUtW+1q4JB1Ly4Bj54chfwI=
 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 d8ece28..7f71f13 100644
--- a/reader.go
+++ b/reader.go
@@ -6,19 +6,24 @@ import (
 	"strings"
 
 	"git.milar.in/milarin/ds"
+	"git.milar.in/milarin/slices"
 )
 
 type Reader struct {
-	buf ds.Stack[posRune]
-	src *bufio.Reader
-	pos *Position
+	buf     ds.Stack[posRune]
+	indices ds.Stack[uint64]
+	index   uint64
+	src     *bufio.Reader
+	pos     *Position
 }
 
 func New(r io.Reader) *Reader {
 	return &Reader{
-		buf: ds.NewArrayStack[posRune](),
-		src: bufio.NewReader(r),
-		pos: &Position{Index: 0, Line: 1, Column: 1},
+		buf:     ds.NewArrayStack[posRune](),
+		src:     bufio.NewReader(r),
+		pos:     &Position{Index: 0, Line: 1, Column: 1},
+		index:   0,
+		indices: ds.NewArrayStack[uint64](),
 	}
 }
 
@@ -43,6 +48,7 @@ func (r *Reader) Rune() (rune, error) {
 	if err == nil {
 		r.buf.Push(r.psrn(rn))
 		r.pos.Advance(rn)
+		r.index++
 	}
 	return rn, err
 }
@@ -99,6 +105,8 @@ func (r *Reader) UnreadRune() error {
 		r.src = prependRune(rn.Rune, r.src)
 	}
 
+	r.index--
+
 	return nil
 }
 
@@ -250,8 +258,44 @@ func (r *Reader) ExpectOneOfString(str ...string) (string, bool, error) {
 	return "", false, nil
 }
 
-// Commit clears the internal buffer and therefore removes all data which were already read.
-// After calling Commit any unreads will return ErrNothingToUnread until another read occured.
-func (r *Reader) Commit() {
-	r.buf.Clear()
+func (r *Reader) Push() {
+	r.indices.Push(r.index)
+}
+
+func (r *Reader) Pop() ([]rune, error) {
+	if r.indices.Empty() {
+		return nil, ErrPopFailed.New()
+	}
+
+	lastIndex := r.indices.Pop()
+	currentIndex := r.index
+	if lastIndex < currentIndex {
+		values := make([]rune, 0, int(currentIndex-lastIndex))
+		for i := 0; i < int(currentIndex-lastIndex); i++ {
+			err := r.UnreadRune()
+			if err != nil {
+				return nil, err
+			}
+
+			value, err := r.PeekRune()
+			if err != nil {
+				return nil, err
+			}
+
+			values = append(values, value)
+		}
+		return slices.Reverse(values), nil
+	} else if lastIndex > currentIndex {
+		values := make([]rune, 0, int(lastIndex-currentIndex))
+		for i := 0; i < int(lastIndex-currentIndex); i++ {
+			value, err := r.Rune()
+			if err != nil {
+				return nil, err
+			}
+			values = append(values, value)
+		}
+		return values, nil
+	}
+
+	return []rune{}, nil
 }