first draft of the lexer

lexer.go

@@ -1 +1,197 @@
 package wikilink
+
+import (
+	"fmt"
+	"strings"
+	"unicode/utf8"
+)
+
+const (
+	eof rune = -1
+)
+
+const (
+	openLink  = "[["
+	closeLink = "]]"
+	alias     = "|"
+	blockRef  = "#^"
+)
+
+func lex(name, input string) *lexer {
+	l := &lexer{
+		name:  name,
+		input: input,
+		state: lexText
+		items: make(chan item, 2),
+	}
+	go l.run()
+	return l
+}
+
+func (l *lexer) nextItem() item {
+	for {
+		select {
+		case item := <-l.items:
+			return item
+		default:
+			l.state = l.state(l)
+		}
+	}
+}
+
+func (l *lexer) state(
+
+func (l *lexer) ignore() {
+	l.start = l.pos
+}
+
+func (l *lexer) backup() {
+	l.pos -= l.width
+}
+
+type lexer struct {
+	name, input       string
+	start, pos, width int
+	items             chan item
+}
+
+func (l *lexer) peek() rune {
+	r := l.next()
+	l.backup()
+	return r
+}
+
+func (l *lexer) accept(valid string) bool {
+	if strings.IndexRune(valid, l.next()) >= 0 {
+		return true
+	}
+	l.backup()
+	return false
+}
+
+func (l *lexer) acceptRun(valid string) {
+	for strings.IndexRune(valid, l.next()) >= 0 {
+	}
+	l.backup()
+}
+
+func (l *lexer) emit(t itemType) {
+	l.items <- item{t, l.input[l.start:l.pos]}
+	l.start = l.pos
+}
+
+func (l *lexer) errorf(format string, args ...interface{}) stateFn {
+	l.items <- item{
+		itemError,
+		fmt.Sprintf(format, args...),
+	}
+	return nil
+}
+
+func lexFragment (l *lexer) stateFn
+func lexAlias (l *lexer) stateFn
+
+func lexInsideLink(l *lexer) stateFn {
+	for {
+		if strings.HasPrefix(l.input[l.pos:], closeLink) {
+			return lexCloseLink
+		}
+
+		r := l.next()
+
+		switch {
+		case r == eof:
+		case r == '\n':
+			return l.errorf("unclosed link")
+		case r == "#":
+			next = l.peek()
+			return lexFragment
+		case r == "|":
+			return lexAlias
+		}
+	}
+}
+
+func lexOpenLink(l *lexer) stateFn {
+	l.pos += len(openLink)
+	l.emit(itemOpenLink)
+	return lexInsideLink
+}
+
+func lexCloseLink(l *lexer) stateFn {
+	l.pos += len(closeLink)
+	l.emit(itemCloseLink)
+	return lexText
+}
+
+func lexText(l *lexer) stateFn {
+	for {
+		if strings.HasPrefix(l.input[l.pos:], openLink) {
+			if l.pos > l.start {
+				l.emit(itemText)
+			}
+			return lexOpenLink
+		}
+
+		if l.next() == eof {
+			break
+		}
+		if l.pos > l.start {
+			l.emit(itemText)
+		}
+		l.emit(itemEOF)
+		return nil
+	}
+	return nil
+}
+
+func (l *lexer) next() rune {
+	var r rune
+	if l.pos >= len(l.input) {
+		l.width = 0
+		return eof
+	}
+	r, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
+	l.pos += l.width
+	return r
+}
+
+func (l *lexer) run() {
+	for state := lexText; state != nil; {
+		state = state(l)
+	}
+	close(l.items)
+}
+
+type stateFn func(*lexer) stateFn
+
+type itemType int
+
+const (
+	itemError itemType = iota
+	itemEOF
+	itemText
+	itemOpenLink
+	itemCloseLink
+	itemBlockRef
+	itemAlias
+)
+
+type item struct {
+	typ itemType
+	val string
+}
+
+func (i item) String() string {
+	switch i.typ {
+
+	case itemEOF:
+		return "EOF"
+	case itemError:
+		return i.val
+	}
+	if len(i.val) > 10 {
+		return fmt.Sprintf("%.10q...", i.val)
+	}
+	return fmt.Sprintf("%q...", i.val)
+}