From 643623dbecdc1ccb6f3ac77e4ebabdc6ca1d8d06 Mon Sep 17 00:00:00 2001
From: Thomas Voss <mail@thomasvoss.com>
Date: Sat, 2 Sep 2023 18:49:53 +0200
Subject: Genesis commit

---
 parser/reader.go | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 parser/reader.go

(limited to 'parser/reader.go')

diff --git a/parser/reader.go b/parser/reader.go
new file mode 100644
index 0000000..22a8e6f
--- /dev/null
+++ b/parser/reader.go
@@ -0,0 +1,94 @@
+package parser
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"unicode"
+	"unicode/utf8"
+)
+
+type position struct {
+	col     uint
+	row     uint
+	prevCol uint
+}
+
+func (p position) String() string {
+	return fmt.Sprintf("%d:%d", p.row+1, p.col)
+}
+
+type reader struct {
+	r   *bufio.Reader
+	pos position
+}
+
+func (reader *reader) peekRune() (rune, error) {
+	bytes := make([]byte, 0, 4)
+	var err error
+
+	// Peeking the next rune is annoying.  We want to get the next rune
+	// which could be the next 1–4 bytes.  Normally we can just call
+	// reader.r.Peek(4) but that doesn’t work here as the last rune in a
+	// file could be a 1–3 byte rune, so we would fail with an EOF error.
+	for i := 4; i > 0; i-- {
+		if bytes, err = reader.r.Peek(i); err == io.EOF {
+			continue
+		} else if err != nil {
+			return 0, err
+		} else {
+			rune, _ := utf8.DecodeRune(bytes)
+			return rune, nil
+		}
+	}
+
+	return 0, io.EOF
+}
+
+func (reader *reader) unreadRune() error {
+	if reader.pos.col == 0 {
+		reader.pos.col = reader.pos.prevCol
+		reader.pos.row--
+	} else {
+		reader.pos.col--
+	}
+	
+	return reader.r.UnreadRune()
+}
+
+func (reader *reader) readRune() (rune, error) {
+	rune, _, err := reader.r.ReadRune()
+	if rune == '\n' {
+		reader.pos.prevCol = reader.pos.col
+		reader.pos.col = 0
+		reader.pos.row++
+	} else {
+		reader.pos.col++
+	}
+	return rune, err
+}
+
+func (reader *reader) readNonSpaceRune() (rune, error) {
+	if err := reader.skipSpaces(); err != nil {
+		return 0, err
+	}
+
+	if r, err := reader.readRune(); err != nil {
+		return 0, err
+	} else {
+		return r, nil
+	}
+}
+
+func (reader *reader) skipSpaces() error {
+	for {
+		if rune, err := reader.readRune(); err != nil {
+			if err == io.EOF {
+				return nil
+			}
+			return err
+		} else if !unicode.IsSpace(rune) {
+			return reader.unreadRune()
+		}
+	}
+}
-- 
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