Push and Pop added

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
 }