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// Package buffruneio is a wrapper around bufio to provide buffered runes access with unlimited unreads.
package buffruneio
import (
"bufio"
"container/list"
"errors"
"io"
)
// Rune to indicate end of file.
const (
EOF = -(iota + 1)
)
// ErrNoRuneToUnread is returned by UnreadRune() when the read index is already at the beginning of the buffer.
var ErrNoRuneToUnread = errors.New("no rune to unwind")
// Reader implements runes buffering for an io.Reader object.
type Reader struct {
buffer *list.List
current *list.Element
input *bufio.Reader
}
// NewReader returns a new Reader.
func NewReader(rd io.Reader) *Reader {
return &Reader{
buffer: list.New(),
input: bufio.NewReader(rd),
}
}
func (rd *Reader) feedBuffer() error {
r, _, err := rd.input.ReadRune()
if err != nil {
if err != io.EOF {
return err
}
r = EOF
}
rd.buffer.PushBack(r)
if rd.current == nil {
rd.current = rd.buffer.Back()
}
return nil
}
// ReadRune reads the next rune from buffer, or from the underlying reader if needed.
func (rd *Reader) ReadRune() (rune, error) {
if rd.current == rd.buffer.Back() || rd.current == nil {
err := rd.feedBuffer()
if err != nil {
return EOF, err
}
}
r := rd.current.Value
rd.current = rd.current.Next()
return r.(rune), nil
}
// UnreadRune pushes back the previously read rune in the buffer, extending it if needed.
func (rd *Reader) UnreadRune() error {
if rd.current == rd.buffer.Front() {
return ErrNoRuneToUnread
}
if rd.current == nil {
rd.current = rd.buffer.Back()
} else {
rd.current = rd.current.Prev()
}
return nil
}
// Forget removes runes stored before the current stream position index.
func (rd *Reader) Forget() {
if rd.current == nil {
rd.current = rd.buffer.Back()
}
for ; rd.current != rd.buffer.Front(); rd.buffer.Remove(rd.current.Prev()) {
}
}
// Peek returns at most the next n runes, reading from the uderlying source if
// needed. Does not move the current index. It includes EOF if reached.
func (rd *Reader) Peek(n int) []rune {
res := make([]rune, 0, n)
cursor := rd.current
for i := 0; i < n; i++ {
if cursor == nil {
err := rd.feedBuffer()
if err != nil {
return res
}
cursor = rd.buffer.Back()
}
if cursor != nil {
r := cursor.Value.(rune)
res = append(res, r)
if r == EOF {
return res
}
cursor = cursor.Next()
}
}
return res
}
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