parser: introduce generic-ish TextParser

Signed-off-by: Alejandro Mery <amery@jpi.io>

parser/text.go

@@ -0,0 +1,76 @@
+package parser
+
+import (
+	"bytes"
+	"io"
+	"strings"
+
+	"asciigoat.org/core/lexer"
+)
+
+// TextParser is a generic text parser.
+type TextParser struct {
+	*lexer.Reader
+	pos lexer.Position
+}
+
+// Init initializes the [TextParser] with a non-nil [io.Reader].
+func (p *TextParser) Init(r io.Reader) {
+	switch {
+	case p == nil || r == nil:
+		panic("invalid call")
+	case p.Reader != nil:
+		panic("parser already initialized")
+	default:
+		p.Reader = lexer.NewReader(r)
+		p.pos.Reset()
+	}
+}
+
+// InitBytes initializes the [TextParser] with a byte array
+func (p *TextParser) InitBytes(b []byte) {
+	p.Init(bytes.NewReader(b))
+}
+
+// InitString initializes the [TextParser] with a byte array
+func (p *TextParser) InitString(s string) {
+	p.Init(strings.NewReader(s))
+}
+
+// Discard shadows [lexer.Reader]'s, and takes in consideration
+// new lines on the discarded data when moving the position
+func (*TextParser) Discard() {
+	// TODO: consider new lines
+	panic("not implemented")
+}
+
+// Emit returns the accepted text, its position, and
+// moves the cursor position accordingly
+func (p *TextParser) Emit() (lexer.Position, string) {
+	pos := p.pos
+	s := p.Reader.Emit()
+	// TODO: consider new lines
+	p.pos.StepN(len(s))
+
+	return pos, s
+}
+
+// Step discards what's been accepted and increments the
+// position assuming they all increment the column counter
+func (p *TextParser) Step() {
+	s := p.Reader.Emit()
+	p.pos.StepN(len(s))
+}
+
+// StepLine discards what's been accepted and moves then
+// position to the beginning of the next line
+func (p *TextParser) StepLine() {
+	p.Reader.Discard()
+	p.pos.StepLine()
+}
+
+// Position returns the position of the first character
+// of the accepted text
+func (p *TextParser) Position() lexer.Position {
+	return p.pos
+}