From 094acf98ca2668304a9a371c25aa5f0359388ecd Mon Sep 17 00:00:00 2001
From: Timon Ringwald <timon.ringwald@mequen.de>
Date: Tue, 19 Apr 2022 14:35:10 +0200
Subject: [PATCH] initial commit

---
 errors.go |  9 +++++++
 go.mod    |  8 ++++++
 go.sum    |  4 +++
 reader.go | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 utils.go  | 15 +++++++++++
 5 files changed, 117 insertions(+)
 create mode 100644 errors.go
 create mode 100644 go.mod
 create mode 100644 go.sum
 create mode 100644 reader.go
 create mode 100644 utils.go

diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..72bfa8d
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,9 @@
+package bufr
+
+import (
+	"git.tordarus.net/Tordarus/adverr"
+)
+
+var (
+	ErrNothingToUnread = adverr.NewErrTmpl("ErrNothingToUnread", "Unreading failed because there wasn't any Read yet")
+)
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..ec51b77
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,8 @@
+module git.tordarus.net/Tordarus/bufr
+
+go 1.18
+
+require (
+	git.tordarus.net/Tordarus/adverr v0.2.0
+	git.tordarus.net/Tordarus/dstruct v0.0.2
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..3173da5
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,4 @@
+git.tordarus.net/Tordarus/adverr v0.2.0 h1:kLYjR2/Vb2GHiSAMvAv+WPNaHR9BRphKanf8H/pCZdA=
+git.tordarus.net/Tordarus/adverr v0.2.0/go.mod h1:XRf0+7nhOkIEr0gi9DUG4RvV2KaOFB0fYPDaR1KLenw=
+git.tordarus.net/Tordarus/dstruct v0.0.2 h1:oFaZO7YXQeHjxL4DmMaZ+Eb4MvP23dX8GAXs0Z6VQKo=
+git.tordarus.net/Tordarus/dstruct v0.0.2/go.mod h1:RvLL2G4lUCGzwr8KaBGQRi3qlMG0WTgGhcVN6iyZZuw=
diff --git a/reader.go b/reader.go
new file mode 100644
index 0000000..379ff82
--- /dev/null
+++ b/reader.go
@@ -0,0 +1,81 @@
+package bufr
+
+import (
+	"bufio"
+	"io"
+	"strings"
+
+	"git.tordarus.net/Tordarus/dstruct"
+)
+
+type Reader struct {
+	buf *dstruct.Stack[rune]
+	src *bufio.Reader
+}
+
+func NewReader(r io.Reader) *Reader {
+	return &Reader{
+		buf: new(dstruct.Stack[rune]),
+		src: bufio.NewReader(r),
+	}
+}
+
+// Rune returns the next rune in r
+func (r *Reader) Rune() (rune, error) {
+	rn, _, err := r.src.ReadRune()
+	if err == nil {
+		r.buf.Push(rn)
+	}
+	return rn, err
+}
+
+// UnreadRune unreads the last rune.
+// The next read will include the unread rune.
+// It returns ErrNothingToUnread if there wasn't any read yet
+func (r *Reader) UnreadRune() error {
+	if r.buf.Empty() {
+		return ErrNothingToUnread.New()
+	}
+
+	if err := r.src.UnreadRune(); err == nil {
+		r.buf.Pop()
+	} else {
+		r.src = prependRune(r.buf.Pop(), r.src)
+	}
+
+	return nil
+}
+
+// UnreadString calls UnreadRune for each rune in str
+// The actual runes are irrelevant.
+// Only the rune count of str determines the amount of UnreadRune calls.
+// The first error occured will be returned immediately.
+func (r *Reader) UnreadString(str string) error {
+	for range str {
+		err := r.UnreadRune()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// StringWhile reads runes and calls f for each one.
+// It returns all runes as a string for which f returned true.
+// It stops when f returns false or an error occured.
+// The rune for which f returned false will not be unread.
+func (r *Reader) StringWhile(f func(rn rune) bool) (string, error) {
+	s := new(strings.Builder)
+
+	var err error
+	for rn, err := r.Rune(); err == nil && f(rn); rn, err = r.Rune() {
+		s.WriteRune(rn)
+	}
+
+	return s.String(), err
+}
+
+// StringUntil is a shorthand for r.StringWhile(func(rn rune) bool { return !f(rn) })
+func (r *Reader) StringUntil(f func(rn rune) bool) (string, error) {
+	return r.StringWhile(func(rn rune) bool { return !f(rn) })
+}
diff --git a/utils.go b/utils.go
new file mode 100644
index 0000000..f0f633c
--- /dev/null
+++ b/utils.go
@@ -0,0 +1,15 @@
+package bufr
+
+import (
+	"bufio"
+	"io"
+	"strings"
+)
+
+func prependString(str string, r io.Reader) *bufio.Reader {
+	return bufio.NewReader(io.MultiReader(strings.NewReader(str), r))
+}
+
+func prependRune(rn rune, r io.Reader) *bufio.Reader {
+	return prependString(string(rn), r)
+}