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lexer.go
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lexer.go
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package css
import (
"fmt"
"unicode/utf8"
"strings"
)
const (
itemError itemType = iota
itemEOF
itemProp
itemValue
)
const eof = 0
type itemType int
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)
}
type stateFn func(*lexer) stateFn
type lexer struct {
input string
start int
pos int
width int
items chan item
state stateFn
}
func lex(input string) *lexer {
l := lexer{
input: input,
items: make(chan item, 2),
state: lexProp,
}
return &l
}
func (l *lexer) nextItem() item {
for {
select {
case i := <-l.items:
return i
default:
l.state = l.state(l)
}
}
}
func lexProp(l *lexer) stateFn {
l.acceptRun(";\n \t")
l.ignore()
if l.peek() == eof {
l.emit(itemEOF)
close(l.items)
return nil
}
if !l.accept("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_") {
return l.errorf("bad property name syntax: it must start with a letter")
}
l.acceptRun("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_")
l.emit(itemProp)
return lexDelimiter
}
func lexDelimiter(l *lexer) stateFn {
l.acceptRun(" \t")
l.ignore()
if l.next() != ':' {
l.errorf("bad property: value format: expected ':' but not found")
}
return lexValue
}
func lexValue(l *lexer) stateFn {
l.acceptRun(" \t\n")
l.ignore()
for {
switch r := l.peek(); r {
case '\'':
if false == l.acceptSingleQuoteString() {
return nil
}
case '"':
if false == l.acceptDoubleQuoteString() {
return nil
}
case ';':
l.emit(itemValue)
l.next()
l.ignore()
return lexProp
case eof:
if l.pos == l.start {
return l.errorf("bad value format: expected not empty value")
}
l.emit(itemValue)
l.next()
l.ignore()
l.emit(itemEOF)
return nil
default:
l.next()
}
}
}
func (l *lexer) emit(t itemType) {
l.items <- item{t, l.input[l.start:l.pos]}
l.start = l.pos
}
func (l *lexer) next() (rune rune) {
if l.pos >= len(l.input) {
l.width = 0
return eof
}
rune, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
l.pos += l.width
return rune
}
func (l *lexer) ignore() {
l.start = l.pos
}
func (l *lexer) backup() {
l.pos -= l.width
}
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) errorf(format string, args ...interface{}) stateFn {
l.items <- item{
itemError,
fmt.Sprintf(format, args...),
}
return nil
}
func (l *lexer) acceptSingleQuoteString() bool {
l.next()
for {
switch r := l.next(); r {
case '\'':
return true
case '\\':
l.next()
case eof:
l.errorf("unexpected EOF: expected closing single quote", )
return false
}
}
}
func (l *lexer) acceptDoubleQuoteString() bool {
l.next()
for {
switch r := l.next(); r {
case '"':
return true
case '\\':
l.next()
case eof:
l.errorf("unexpected EOF: expected closing double quote", )
return false
}
}
}