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scanner.go
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scanner.go
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package bibtex
import (
"bufio"
"bytes"
"io"
"log"
"strconv"
"strings"
)
var parseField bool
// scanner is a lexical scanner
type scanner struct {
r *bufio.Reader
pos tokenPos
}
// newScanner returns a new instance of scanner.
func newScanner(r io.Reader) *scanner {
return &scanner{r: bufio.NewReader(r), pos: tokenPos{Char: 0, Lines: []int{}}}
}
// read reads the next rune from the buffered reader.
// Returns the rune(0) if an error occurs (or io.eof is returned).
func (s *scanner) read() rune {
ch, _, err := s.r.ReadRune()
if err != nil {
return eof
}
if ch == '\n' {
s.pos.Lines = append(s.pos.Lines, s.pos.Char)
s.pos.Char = 0
} else {
s.pos.Char++
}
return ch
}
// unread places the previously read rune back on the reader.
func (s *scanner) unread() {
_ = s.r.UnreadRune()
if s.pos.Char == 0 {
s.pos.Char = s.pos.Lines[len(s.pos.Lines)-1]
s.pos.Lines = s.pos.Lines[:len(s.pos.Lines)-1]
} else {
s.pos.Char--
}
}
// Scan returns the next token and literal value.
func (s *scanner) Scan() (tok token, lit string) {
ch := s.read()
if isWhitespace(ch) {
s.ignoreWhitespace()
ch = s.read()
}
if isAlphanum(ch) {
s.unread()
return s.scanIdent()
}
switch ch {
case eof:
return 0, ""
case '@':
return tATSIGN, string(ch)
case ':':
return tCOLON, string(ch)
case ',':
parseField = false // reset parseField if reached end of field.
return tCOMMA, string(ch)
case '=':
parseField = true // set parseField if = sign outside quoted or ident.
return tEQUAL, string(ch)
case '"':
return s.scanQuoted()
case '{':
if parseField {
return s.scanBraced()
}
return tLBRACE, string(ch)
case '}':
if parseField { // reset parseField if reached end of entry.
parseField = false
}
return tRBRACE, string(ch)
case '#':
return tPOUND, string(ch)
case ' ':
s.ignoreWhitespace()
}
return tILLEGAL, string(ch)
}
// scanIdent categorises a string to one of three categories.
func (s *scanner) scanIdent() (tok token, lit string) {
switch ch := s.read(); ch {
case '"':
return s.scanQuoted()
case '{':
return s.scanBraced()
default:
s.unread() // Not open quote/brace.
return s.scanBare()
}
}
func (s *scanner) scanBare() (token, string) {
var buf bytes.Buffer
for {
if ch := s.read(); ch == eof {
break
} else if !isAlphanum(ch) && !isBareSymbol(ch) || isWhitespace(ch) {
s.unread()
break
} else {
_, _ = buf.WriteRune(ch)
}
}
str := buf.String()
if strings.ToLower(str) == "comment" {
return tCOMMENT, str
} else if strings.ToLower(str) == "preamble" {
return tPREAMBLE, str
} else if strings.ToLower(str) == "string" {
return tSTRING, str
} else if _, err := strconv.Atoi(str); err == nil && parseField { // Special case for numeric
return tIDENT, str
}
return tBAREIDENT, str
}
// scanBraced parses a braced string, like {this}.
func (s *scanner) scanBraced() (token, string) {
var buf bytes.Buffer
var macro bool
brace := 1
for {
if ch := s.read(); ch == eof {
break
} else if ch == '\\' {
_, _ = buf.WriteRune(ch)
macro = true
} else if ch == '{' {
_, _ = buf.WriteRune(ch)
brace++
} else if ch == '}' {
brace--
macro = false
if brace == 0 { // Balances open brace.
return tIDENT, buf.String()
}
_, _ = buf.WriteRune(ch)
} else if ch == '@' {
if macro {
_, _ = buf.WriteRune(ch)
} else {
log.Fatalf("%s: %s", ErrUnexpectedAtsign, buf.String())
}
} else if isWhitespace(ch) {
_, _ = buf.WriteRune(ch)
macro = false
} else {
_, _ = buf.WriteRune(ch)
}
}
return tILLEGAL, buf.String()
}
// scanQuoted parses a quoted string, like "this".
func (s *scanner) scanQuoted() (token, string) {
var buf bytes.Buffer
brace := 0
for {
if ch := s.read(); ch == eof {
break
} else if ch == '{' {
brace++
} else if ch == '}' {
brace--
} else if ch == '"' {
if brace == 0 { // Matches open quote, unescaped
return tIDENT, buf.String()
}
_, _ = buf.WriteRune(ch)
} else {
_, _ = buf.WriteRune(ch)
}
}
return tILLEGAL, buf.String()
}
// ignoreWhitespace consumes the current rune and all contiguous whitespace.
func (s *scanner) ignoreWhitespace() {
for {
if ch := s.read(); ch == eof {
break
} else if !isWhitespace(ch) {
s.unread()
break
}
}
}